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S. Matile - One of the best experts on this subject based on the ideXlab platform.
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synthetic multifunctional pores that open and close in response to chemical stimulation
Bioorganic & Medicinal Chemistry, 2005Co-Authors: V. Gorteau, G. Bollot, J. Mareda, D. Pasini, N. Sakai, Duyhien Tran, Adina N Lazar, Anthony W Coleman, S. MatileAbstract:Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.
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Synthetic multifunctional pores that open and close in response to chemical stimulation.
Bioorganic and Medicinal Chemistry, 2005Co-Authors: V. Gorteau, G. Bollot, J. Mareda, D. Pasini, Dh Tran, An Lazar, Aw Coleman, N. Sakai, S. MatileAbstract:Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.
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α-Helix recognition by rigid-rod β-Barrel ion channels with internal arginine-histidine dyads in polarized bilayer membranes
Journal of Supramolecular Chemistry, 2002Co-Authors: Nathalie Sordé, S. MatileAbstract:The objective of this study was to exploit multifunctional rigid-rod ß-Barrel ion channels for a-helix recognition by dipole-potential interactions in polarized membranes. Synthesis and evaluation of artificial ß-Barrel 1 characterized by p-octiphenyl ‘staves,' leucine residues at the outer and histidine as well as, for the first time, arginine residues at the inner Barrel Surface are described. Internal arginines were introduced to recognize organic ions such as a-helical poly-Image -glutamic acid (a-PLGA) passing through pores formed by Barrel 1 at nanomolar concentrations. In unpolarized spherical bilayers (EYPC-LUVs), P-helical a-PLGA blocked pore 1 with a KD=150 nM at pH=4.5. As expected for a highly symmetric supramolecular host, a KD=100 nM determined for M-helical a-PDGA at pH=4.5 did not support substantial chiral guest recognition. Decreasing KD's with increasing pH indicated that, in unpolarized bilayers, pore 1 recognizes anions (rather than a-helices). In polarized spherical membranes, the KD for a-PLGA at pH=4.5 dropped substantially to 13 nM at V ˜-150 mV. This experimental support for operational dipole-potential interactions indicates that a-PLGAs bind within active pores in transmembrane orientation with intravesicular N- and extravesicular C-termini. Independence on bilayer polarization for binding of random-coil PLGA at pH=5.5 corroborated that dipole–potential interactions account for a-helix recognition in polarized membranes
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α-Helix recognition by rigid-rod β-Barrel ion channels with internal arginine-histidine dyads in polarized bilayer membranes
Journal of Supramolecular Chemistry, 2002Co-Authors: Nathalie Sordé, S. MatileAbstract:Abstract The objective of this study was to exploit multifunctional rigid-rod β-Barrel ion channels for α-helix recognition by dipole-potential interactions in polarized membranes. Synthesis and evaluation of artificial β-Barrel 1 characterized by p-octiphenyl ‘staves,’ leucine residues at the outer and histidine as well as, for the first time, arginine residues at the inner Barrel Surface are described. Internal arginines were introduced to recognize organic ions such as α-helical poly- l -glutamic acid (α-PLGA) passing through pores formed by Barrel 1 at nanomolar concentrations. In unpolarized spherical bilayers (EYPC-LUVs), P-helical α-PLGA blocked pore 1 with a KD=150 nM at pH=4.5. As expected for a highly symmetric supramolecular host, a KD=100 nM determined for M-helical α-PDGA at pH=4.5 did not support substantial chiral guest recognition. Decreasing KD's with increasing pH indicated that, in unpolarized bilayers, pore 1 recognizes anions (rather than α-helices). In polarized spherical membranes, the KD for α-PLGA at pH=4.5 dropped substantially to 13 nM at V ≈−150 mV. This experimental support for operational dipole-potential interactions indicates that α-PLGAs bind within active pores in transmembrane orientation with intravesicular N- and extravesicular C-termini. Independence on bilayer polarization for binding of random-coil PLGA at pH=5.5 corroborated that dipole–potential interactions account for α-helix recognition in polarized membranes.
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Toward catalytic rigid‐rod β‐Barrels: A hexamer with multiple histidines
Chirality, 2001Co-Authors: Gopal Das, N. Sakai, S. MatileAbstract:Rigid-rod beta-Barrels are composed of interdigitating, short, amphiphilic peptide strands that are flanked by stabilizing rigid-rod "staves." As a first step toward the construction of catalytic rigid-rod beta-Barrels, we here report synthesis and study of a new Barrel designed to comprise alternating leucine and histidine residues at the inner and lysine and glutamate residues at the outer Barrel Surface. Synthesis of p-octiphenyls with lateral tripeptide strands followed procedures described previously. Barrel formation by programmed assembly of complementary tripeptide-p-octiphenyl rods was monitored by circular dichroism (CD). CD-mixing curves (Job-plots) were consistent with 1:1-stoichiometry. Guanidinium chloride denaturation experiments gave a DeltaG(H20) = -1.8 kcal mol(-1) with a C(50) = 1.9 M. Size exclusion chromatography suggested quantitative formation of a hexamer. Facile Barrel deconstruction by acid and divalent cations demonstrated the presence of internal, nonproximal histidines. Inclusion complex formation with fluorescent guests corroborated internal hydrophobicity of beta-Barrel hosts and potential for intratoroidal catalysis.
Timo K Korhonen - One of the best experts on this subject based on the ideXlab platform.
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Fibrinolytic and coagulative activities of Yersinia pestis
Frontiers in cellular and infection microbiology, 2013Co-Authors: Timo K Korhonen, Johanna Haiko, Liisa Laakkonen, Hanna M. Järvinen, Benita Westerlund-wikströmAbstract:The outer membrane protease Pla belongs to the omptin protease family spread by horizontal gene transfer into Gram-negative bacteria that infect animals or plants. Pla has adapted to support the life style of the plague bacterium Yersinia pestis. Pla has a -Barrel fold with 10 membrane-spanning strands and five Surface loops, and the Barrel Surface contains bound lipopolysaccharide (LPS) that is critical for the conformation and the activity of Pla. The biological activity of Pla is influenced by the structure of the Surface loops around the active site groove and by temperature-induced LPS modifications. Several of the putative virulence-related functions documented for Pla in vitro address control of the human hemostatic system, i.e. coagulation and fibrinolysis. Pla activates human plasminogen to the serine protease plasmin and activates the physiological plasminogen activator urokinase. Pla also inactivates the protease inhibitors alpha-2-antiplasmin and plasminogen activator inhibitor 1 and prevents the activation of thrombin-activatable fibrinolysis inhibitor. These functions enhance uncontrolled fibrinolysis which is thought to improve Y. pestis dissemination and survival in the mammalian host, and lowered fibrin(ogen) deposition has indeed been observed in mice infected with Pla-positive Y. pestis. However, Pla also inactivates an anticoagulant, the tissue factor pathway inhibitor, which should increase fibrin formation and clotting. Thus Pla and Y. pestis have complex interactions with the hemostatic system. Y. pestis modifies its LPS upon transfer to the mammalian host and we hypothesize that the contrasting biological activities of Pla in coagulation and fibrinolysis are influenced by LPS changes during infection.
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Molecular adaptation of a plant-bacterium outer membrane protease towards plague virulence factor Pla
BMC Evolutionary Biology, 2011Co-Authors: Johanna Haiko, Liisa Laakkonen, Benita Westerlund-wikström, Timo K KorhonenAbstract:Background Omptins are a family of outer membrane proteases that have spread by horizontal gene transfer in Gram-negative bacteria that infect vertebrates or plants. Despite structural similarity, the molecular functions of omptins differ in a manner that reflects the life style of their host bacteria. To simulate the molecular adaptation of omptins, we applied site-specific mutagenesis to make Epo of the plant pathogenic Erwinia pyrifoliae exhibit virulence-associated functions of its close homolog, the plasminogen activator Pla of Yersinia pestis . We addressed three virulence-associated functions exhibited by Pla, i.e., proteolytic activation of plasminogen, proteolytic degradation of serine protease inhibitors, and invasion into human cells. Results Pla and Epo expressed in Escherichia coli are both functional endopeptidases and cleave human serine protease inhibitors, but Epo failed to activate plasminogen and to mediate invasion into a human endothelial-like cell line. Swapping of ten amino acid residues at two Surface loops of Pla and Epo introduced plasminogen activation capacity in Epo and inactivated the function in Pla. We also compared the structure of Pla and the modeled structure of Epo to analyze the structural variations that could rationalize the different proteolytic activities. Epo-expressing bacteria managed to invade human cells only after all extramembranous residues that differ between Pla and Epo and the first transmembrane β-strand had been changed. Conclusions We describe molecular adaptation of a protease from an environmental setting towards a virulence factor detrimental for humans. Our results stress the evolvability of bacterial β-Barrel Surface structures and the environment as a source of progenitor virulence molecules of human pathogens.
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lack of o antigen is essential for plasminogen activation by yersinia pestis and salmonella enterica
Molecular Microbiology, 2003Co-Authors: Maini Kukkonen, Ilkka M. Helander, Marjo Suomalainen, Paivi Kyllonen, Kaarina Lahteenmaki, Hannu Lang, Ritva Virkola, Otto Holst, Timo K KorhonenAbstract:Summary The O-antigen of lipopolysaccharide (LPS) is a virulence factor in enterobacterial infections, and the advantage of its genetic loss in the lethal pathogen Yersinia pestis has remained unresolved. Y. pestis and Salmonella enterica express β-Barrel Surface proteases of the omptin family that activate human plasminogen. Plasminogen activation is central in pathogenesis of plague but has not, however, been found to be important in diarrhoeal disease. We observed that the presence of O-antigen repeats on wild-type or recombinant S. enterica, Yersinia pseudotuberculosis or Escherichia coli prevents plasminogen activation by PgtE of S. enterica and Pla of Y. pestis; the O-antigen did not affect incorporation of the omptins into the bacterial outer membrane. Purified His6-Pla was successfully reconstituted with rough LPS but remained inactive after reconstitution with smooth LPS. Expression of smooth LPS prevented Pla-mediated adhesion of recombinant E. coli to basement membrane as well as invasion into human endothelial cells. Similarly, the presence of an O-antigen prevented PgtE-mediated bacterial adhesion to basement membrane. Substitution of Arg-138 and Arg-171 of the motif for protein binding to lipid A 4′-phosphate abolished proteolytic activity but not membrane translocation of PgtE, indicating dependence of omptin activity on a specific interaction with lipid A. The results suggest that Pla and PgtE require LPS for activity and that the O-antigen sterically prevents recognition of large-molecular-weight substrates. Loss of O-antigen facilitates Pla functions and invasiveness of Y. pestis; on the other hand, smooth LPS renders plasminogen activator cryptic in S. enterica.
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Lack of O‐antigen is essential for plasminogen activation by Yersinia pestis and Salmonella enterica
Molecular microbiology, 2003Co-Authors: Maini Kukkonen, Ilkka M. Helander, Marjo Suomalainen, Paivi Kyllonen, Kaarina Lahteenmaki, Hannu Lang, Ritva Virkola, Otto Holst, Timo K KorhonenAbstract:Summary The O-antigen of lipopolysaccharide (LPS) is a virulence factor in enterobacterial infections, and the advantage of its genetic loss in the lethal pathogen Yersinia pestis has remained unresolved. Y. pestis and Salmonella enterica express β-Barrel Surface proteases of the omptin family that activate human plasminogen. Plasminogen activation is central in pathogenesis of plague but has not, however, been found to be important in diarrhoeal disease. We observed that the presence of O-antigen repeats on wild-type or recombinant S. enterica, Yersinia pseudotuberculosis or Escherichia coli prevents plasminogen activation by PgtE of S. enterica and Pla of Y. pestis; the O-antigen did not affect incorporation of the omptins into the bacterial outer membrane. Purified His6-Pla was successfully reconstituted with rough LPS but remained inactive after reconstitution with smooth LPS. Expression of smooth LPS prevented Pla-mediated adhesion of recombinant E. coli to basement membrane as well as invasion into human endothelial cells. Similarly, the presence of an O-antigen prevented PgtE-mediated bacterial adhesion to basement membrane. Substitution of Arg-138 and Arg-171 of the motif for protein binding to lipid A 4′-phosphate abolished proteolytic activity but not membrane translocation of PgtE, indicating dependence of omptin activity on a specific interaction with lipid A. The results suggest that Pla and PgtE require LPS for activity and that the O-antigen sterically prevents recognition of large-molecular-weight substrates. Loss of O-antigen facilitates Pla functions and invasiveness of Y. pestis; on the other hand, smooth LPS renders plasminogen activator cryptic in S. enterica.
V. Gorteau - One of the best experts on this subject based on the ideXlab platform.
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synthetic multifunctional pores that open and close in response to chemical stimulation
Bioorganic & Medicinal Chemistry, 2005Co-Authors: V. Gorteau, G. Bollot, J. Mareda, D. Pasini, N. Sakai, Duyhien Tran, Adina N Lazar, Anthony W Coleman, S. MatileAbstract:Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.
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Synthetic multifunctional pores that open and close in response to chemical stimulation.
Bioorganic and Medicinal Chemistry, 2005Co-Authors: V. Gorteau, G. Bollot, J. Mareda, D. Pasini, Dh Tran, An Lazar, Aw Coleman, N. Sakai, S. MatileAbstract:Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.
N. Sakai - One of the best experts on this subject based on the ideXlab platform.
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synthetic multifunctional pores that open and close in response to chemical stimulation
Bioorganic & Medicinal Chemistry, 2005Co-Authors: V. Gorteau, G. Bollot, J. Mareda, D. Pasini, N. Sakai, Duyhien Tran, Adina N Lazar, Anthony W Coleman, S. MatileAbstract:Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.
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Synthetic multifunctional pores that open and close in response to chemical stimulation.
Bioorganic and Medicinal Chemistry, 2005Co-Authors: V. Gorteau, G. Bollot, J. Mareda, D. Pasini, Dh Tran, An Lazar, Aw Coleman, N. Sakai, S. MatileAbstract:Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.Studies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-Barrel pores is precisely reflected in the function: molecular recognition at the outer Barrel Surface results in pore opening, while molecular recognition at the inner Barrel Surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function.
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Toward catalytic rigid‐rod β‐Barrels: A hexamer with multiple histidines
Chirality, 2001Co-Authors: Gopal Das, N. Sakai, S. MatileAbstract:Rigid-rod beta-Barrels are composed of interdigitating, short, amphiphilic peptide strands that are flanked by stabilizing rigid-rod "staves." As a first step toward the construction of catalytic rigid-rod beta-Barrels, we here report synthesis and study of a new Barrel designed to comprise alternating leucine and histidine residues at the inner and lysine and glutamate residues at the outer Barrel Surface. Synthesis of p-octiphenyls with lateral tripeptide strands followed procedures described previously. Barrel formation by programmed assembly of complementary tripeptide-p-octiphenyl rods was monitored by circular dichroism (CD). CD-mixing curves (Job-plots) were consistent with 1:1-stoichiometry. Guanidinium chloride denaturation experiments gave a DeltaG(H20) = -1.8 kcal mol(-1) with a C(50) = 1.9 M. Size exclusion chromatography suggested quantitative formation of a hexamer. Facile Barrel deconstruction by acid and divalent cations demonstrated the presence of internal, nonproximal histidines. Inclusion complex formation with fluorescent guests corroborated internal hydrophobicity of beta-Barrel hosts and potential for intratoroidal catalysis.
Yeh-sun Hong - One of the best experts on this subject based on the ideXlab platform.
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A comparative study of Cr−X−N (X=Zr, Si) coatings for the improvement of the low-speed torque efficiency of a hydraulic piston pump
Metals and Materials International, 2008Co-Authors: Yeh-sun Hong, Sang-yul LeeAbstract:The internal parts of hydraulic pumps operating at variable speed should be protected from insufficient lubrication. The axial piston type pumps employ a steel-base cylinder Barrel rotating on a soft bronze valves plate with a slide contact, where the insufficient lubrication of these components can cause rapid wear of the valve plate and increase the friction loss. In this study, the cylinder Barrel Surface was deposited with CrZrN coatings, which were expected to improve the tribological contact with a valve plate under low-speed mixed lubrication conditions. Its effect on the improvement of the low-speed torque efficiency of a hydraulic piston pump was investigated and compared with that from the CrSiN coating. The coated cylinder Barrels showed much lower friction coefficients and wear rates of the valve plates than the uncoated plasma-nitride one. In particular, the CrZrN coatings revealed better performance than the CrSiN coatings. By representing the improvement in the torque efficiency of the whole pump based upon the degree of the friction coefficient reduction, the CrZrN coatings exhibited approximately a 0.35% higher improvement at 300 bar and 100 rpm than CrSiN coatings. The possible failure modes of the coatings coated on the Barrel were sugested and the microstructures of the coatings seemed to have a strong effect on the film failure mode.
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Effect of CrSiN thin film coating on the improvement of the low-speed torque efficiency of a hydraulic piston pump
Surface & Coatings Technology, 2007Co-Authors: Sang-yul Lee, Yeh-sun HongAbstract:The hydraulic pump used for an electro-hydrostatic actuator operates only when it is directed to compensate for the control error between the input command and the output position. Therefore, its operation is unsteady and intermittent, which leads to poor lubrication of the internal parts. The steel-base cylinder Barrel of an axial piston type pump rotates on a soft bronze valve plate with a slide contact. Therefore, the unsteady lubrication of these components can cause rapid wear of the valve plate. In this study, a CrSiN thin film was deposited on the cylinder Barrel Surface in order to improve its tribological contact with the valve plate under low-speed mixed lubrication conditions. The CrSiN-coated cylinder Barrel showed a much lower friction coefficient and wear rate of the valve plate than the original uncoated one. In addition, its friction coefficient was independent of the normal load, while that of the original cylinder Barrel increased as the normal load increased. If these positive phenomena are represented by the torque efficiency of the test pump, an improvement of more than 1.3% can be achieved at a discharge pressure of 300 bars and a rotational speed of 100 rpm. The wear rate of the valve plate mated with the CrSiN-coated cylinder Barrel was almost negligible.
