The Experts below are selected from a list of 46191 Experts worldwide ranked by ideXlab platform
Ronald T. Hay - One of the best experts on this subject based on the ideXlab platform.
-
Unique binding interactions among Ubc9, SUMO and RanBP2 reveal a mechanism for SUMO paralog selection
Nature structural & molecular biology, 2004Co-Authors: Michael H. Tatham, Yuan Chen, Ellis Jaffray, Suhkmann Kim, Jing Song, Ronald T. HayAbstract:The conjugation of small ubiquitin-like modifiers SUMO-1, SUMO-2 and SUMO-3 onto target proteins requires the concerted action of the specific E1-activating enzyme SAE1/SAE2, the E2-conjugating enzyme Ubc9, and an E3-like SUMO ligase. NMR chemical shift perturbation was used to identify the surface of Ubc9 that interacts with the SUMO ligase RanBP2. Unlike known ubiquitin E2-E3 interactions, RanBP2 binds to the beta-sheet of Ubc9. Mutational disruption of Ubc9-RanBP2 binding affected SUMO-2 but not SUMO-1 conjugation to Sp100 and to a newly identified RanBP2 substrate, PML. RanBP2 contains a binding site specific for SUMO-1 but not SUMO-2, indicating that a Ubc9-SUMO-1 thioester could be recruited to RanBP2 via SUMO-1 in the absence of strong binding between Ubc9 and RanBP2. Thus we show that E2-E3 interactions are not conserved across the ubiquitin-like protein superfamily and identify a RanBP2-dependent mechanism for SUMO paralog-specific conjugation.
-
A Mechanism for Inhibiting the SUMO Pathway
Molecular cell, 2004Co-Authors: Roberto Boggio, Ronald T. Hay, Riccardo Colombo, Giulio Draetta, Susanna ChioccaAbstract:The SUMO pathway parallels the classical ubiquitinylation pathway with three discrete steps: activation involving the enzyme E1, conjugation involving the E2 enzyme UBC9, and substrate modification through the cooperative association of UBC9 and E3 ligases. We report here that the adenoviral protein Gam1 inhibits the SUMO pathway by interfering with the activity of E1 (SAE1/SAE2). In vivo, Gam1 expression leads to SAE1/SAE2 inactivation, both SAE1/SAE2 and UBC9 disappearance, and overall inhibition of protein sumoylation. This results in transcriptional activation of some promoters and is directly linked to inhibition of sumoylation of the transcriptional activators involved. Our results identify a mechanism for interfering with the SUMO pathway and with transcription that could have an impact in the design of novel pharmaceutical agents. They also point out once again to the extraordinary ability of eukaryotic viruses to interfere with the biology of host cells by targeting fundamental biochemical processes.
-
Role of two residues proximal to the active site of Ubc9 in substrate recognition by the Ubc9.SUMO-1 thiolester complex.
Biochemistry, 2003Co-Authors: Michael H. Tatham, Yuan Chen, Ronald T. HayAbstract:The small ubiquitin-like modifier SUMO-1 is covalently attached to lysine residues on target proteins by a specific conjugation pathway involving the El enzyme SAE1/SAE2 and the E2 enzyme Ubc9. In an ATP-dependent manner,the C-terminus of SUMO-1 forms consecutive thiolester bonds with cysteine residues in the SAE2 subunit and Ubc9, before the Ubc9.SUMO-I1thiolester complex catalyzes the formation of an isopeptide bond between SUMO-1 1 and the ∈-amino group of the target lysine residue on the protein substrate. The SUMO- 1 conjugation pathway bears many similarities with that of ubiquitin and other ubiquitin-like protein modifiers (Ub1s), and because of its production of a singly conjugated substrate and the lack of absolute requirement in vitro for E3 enzymes, the SUMO-1/Ubc9 system is a good model for the analysis of protein conjugation pathways that share this basic chemistry. Here we describe methods of both steady-state and half-reaction kinetic analysis of Ubc9, and use these techniques to determine the role of two residues, Asp 1 0 0 and Lys 1 0 1 of Ubc9 which are not found in E2 enzymes from other protein conjugation pathways. These residues are found close to the active site Cys in the tertiary structure of Ubc9, and although they are shown to inhibit the transesterification reaction from SAE1/SAE2, they are important for substrate recognition in the context of the thiolester complex with SUMO-1.
-
polymeric chains of sumo 2 and sumo 3 are conjugated to protein substrates by SAE1 sae2 and ubc9
Journal of Biological Chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
-
Polymeric chains of SUMO-2 and SUMO-3 are conjugated to protein substrates by SAE1/SAE2 and Ubc9
The Journal of biological chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
Michael H. Tatham - One of the best experts on this subject based on the ideXlab platform.
-
Unique binding interactions among Ubc9, SUMO and RanBP2 reveal a mechanism for SUMO paralog selection
Nature structural & molecular biology, 2004Co-Authors: Michael H. Tatham, Yuan Chen, Ellis Jaffray, Suhkmann Kim, Jing Song, Ronald T. HayAbstract:The conjugation of small ubiquitin-like modifiers SUMO-1, SUMO-2 and SUMO-3 onto target proteins requires the concerted action of the specific E1-activating enzyme SAE1/SAE2, the E2-conjugating enzyme Ubc9, and an E3-like SUMO ligase. NMR chemical shift perturbation was used to identify the surface of Ubc9 that interacts with the SUMO ligase RanBP2. Unlike known ubiquitin E2-E3 interactions, RanBP2 binds to the beta-sheet of Ubc9. Mutational disruption of Ubc9-RanBP2 binding affected SUMO-2 but not SUMO-1 conjugation to Sp100 and to a newly identified RanBP2 substrate, PML. RanBP2 contains a binding site specific for SUMO-1 but not SUMO-2, indicating that a Ubc9-SUMO-1 thioester could be recruited to RanBP2 via SUMO-1 in the absence of strong binding between Ubc9 and RanBP2. Thus we show that E2-E3 interactions are not conserved across the ubiquitin-like protein superfamily and identify a RanBP2-dependent mechanism for SUMO paralog-specific conjugation.
-
Role of two residues proximal to the active site of Ubc9 in substrate recognition by the Ubc9.SUMO-1 thiolester complex.
Biochemistry, 2003Co-Authors: Michael H. Tatham, Yuan Chen, Ronald T. HayAbstract:The small ubiquitin-like modifier SUMO-1 is covalently attached to lysine residues on target proteins by a specific conjugation pathway involving the El enzyme SAE1/SAE2 and the E2 enzyme Ubc9. In an ATP-dependent manner,the C-terminus of SUMO-1 forms consecutive thiolester bonds with cysteine residues in the SAE2 subunit and Ubc9, before the Ubc9.SUMO-I1thiolester complex catalyzes the formation of an isopeptide bond between SUMO-1 1 and the ∈-amino group of the target lysine residue on the protein substrate. The SUMO- 1 conjugation pathway bears many similarities with that of ubiquitin and other ubiquitin-like protein modifiers (Ub1s), and because of its production of a singly conjugated substrate and the lack of absolute requirement in vitro for E3 enzymes, the SUMO-1/Ubc9 system is a good model for the analysis of protein conjugation pathways that share this basic chemistry. Here we describe methods of both steady-state and half-reaction kinetic analysis of Ubc9, and use these techniques to determine the role of two residues, Asp 1 0 0 and Lys 1 0 1 of Ubc9 which are not found in E2 enzymes from other protein conjugation pathways. These residues are found close to the active site Cys in the tertiary structure of Ubc9, and although they are shown to inhibit the transesterification reaction from SAE1/SAE2, they are important for substrate recognition in the context of the thiolester complex with SUMO-1.
-
polymeric chains of sumo 2 and sumo 3 are conjugated to protein substrates by SAE1 sae2 and ubc9
Journal of Biological Chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
-
Polymeric chains of SUMO-2 and SUMO-3 are conjugated to protein substrates by SAE1/SAE2 and Ubc9
The Journal of biological chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
Susanna Chiocca - One of the best experts on this subject based on the ideXlab platform.
-
Viral control of the SUMO pathway: Gam1, a model system.
Biochemical Society Transactions, 2007Co-Authors: Susanna ChioccaAbstract:SUMO (small ubiquitin-related modifier) is a ubiquitin-like family member that is conjugated to its substrates through discrete enzymatic steps: activation, involving the E1 enzyme [SAE (SUMO-activating enzyme) 1–SAE2], conjugation, involving the E2 enzyme [Ubc9 (ubiquitin-conjugating enzyme 9)], and substrate modification, through the co-operation of Ubc9 and E3 protein ligases. Work from our laboratory has shown the first example of a viral protein, Gam1, that binds to the E1 heterodimer, inhibiting its function and causing a complete block of the SUMOylation pathway both in vivo and in vitro, followed by SAE1–SAE2 degradation. The mechanism by which a viral protein inactivates and subsequently degrades an essential cellular enzyme, arresting a key regulatory pathway, will be discussed. Although four distinct SUMO isoforms have been described, I will use SUMO to describe the entire system.
-
Targeting SUMO E1 to ubiquitin ligases: a viral strategy to counteract sumoylation.
The Journal of biological chemistry, 2007Co-Authors: Roberto Boggio, Alfonso Passafaro, Susanna ChioccaAbstract:SUMO-1 (small ubiquitin-related modifier-1) is a ubiquitin-like family member that is conjugated to its substrates through three discrete enzymatic steps, activation (involving the E1 enzyme (SAE1/SAE2)), conjugation (involving the E2 enzyme), and substrate modification (through the cooperation of the E2 and E3 protein ligases). The adenoviral protein Gam1 inactivates E1, both in vitro and in vivo, followed by SAE1/SAE2 degradation. We have shown here that Gam1 possesses a C-terminal SOCS domain that allows its interaction with two cellular cullin RING (really interesting new gene) ubiquitin ligases. We demonstrate that Gam1 is necessary for the recruitment of SAE1/SAE2 into Cul2/5-EloB/C-Roc1 ubiquitin ligase complexes and for subsequent SAE1 ubiquitylation and degradation. The degradation of SAE2 is not tightly related to Gam1 but is a consequent effect of SAE1 disappearance. These results reveal the mechanism by which a viral protein inactivates and subsequently degrades an essential cellular enzyme, arresting a key regulatory pathway.
-
Gam1 and the SUMO pathway.
Cell cycle (Georgetown Tex.), 2005Co-Authors: Roberto Boggio, Susanna ChioccaAbstract:Post-translational modifications of proteins have critical roles in many cellular processes because they can cause rapid changes in the functions of preexisting proteins, multiprotein complexes and subcellular structures. Sumoylation, a ubiquitin-like dynamic and reversible post-translational modification system, is an enzymatic cascade leading to the covalent attachment of SUMO to it target proteins. This modification involves three steps and different enzymes: SUMO-activating enzyme E1 (SAE1/SAE2), SUMO-conjugating enzyme E2 (UBC9), SUMO ligases E3s, and SUMO cleaving enzymes. Although the identification of SUMO-modified substrates has progressed rapidly, the biological function of SUMO and regulation of SUMO conjugation are still not well understood. Some viral proteins have been identified as substrates for SUMO modification as well as altering the sumoylation status of host cell proteins. We have been studying an unusual adenoviral protein, Gam1, a strong and global transcriptional activator of both viral and cellular genes that inactivates HDAC1. We have recently expanded the known functions of Gam1 by demonstrating that Gam1 also inhibits the SUMO pathway by interfering with the activity of E1 heterodimer (SAE1/SAE2), leading to the accumulation of SUMO-unmodified substrates. Our data provides a clear example of the effects of a viral infection on host sumoylation and supports the idea that viruses have multifunctional protein that can target essential biochemical pathways.
-
A Mechanism for Inhibiting the SUMO Pathway
Molecular cell, 2004Co-Authors: Roberto Boggio, Ronald T. Hay, Riccardo Colombo, Giulio Draetta, Susanna ChioccaAbstract:The SUMO pathway parallels the classical ubiquitinylation pathway with three discrete steps: activation involving the enzyme E1, conjugation involving the E2 enzyme UBC9, and substrate modification through the cooperative association of UBC9 and E3 ligases. We report here that the adenoviral protein Gam1 inhibits the SUMO pathway by interfering with the activity of E1 (SAE1/SAE2). In vivo, Gam1 expression leads to SAE1/SAE2 inactivation, both SAE1/SAE2 and UBC9 disappearance, and overall inhibition of protein sumoylation. This results in transcriptional activation of some promoters and is directly linked to inhibition of sumoylation of the transcriptional activators involved. Our results identify a mechanism for interfering with the SUMO pathway and with transcription that could have an impact in the design of novel pharmaceutical agents. They also point out once again to the extraordinary ability of eukaryotic viruses to interfere with the biology of host cells by targeting fundamental biochemical processes.
Joana M. P. Desterro - One of the best experts on this subject based on the ideXlab platform.
-
polymeric chains of sumo 2 and sumo 3 are conjugated to protein substrates by SAE1 sae2 and ubc9
Journal of Biological Chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
-
Polymeric chains of SUMO-2 and SUMO-3 are conjugated to protein substrates by SAE1/SAE2 and Ubc9
The Journal of biological chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
-
Identification of the Enzyme Required for Activation of the Small Ubiquitin-like Protein SUMO-1
The Journal of biological chemistry, 1999Co-Authors: Joana M. P. Desterro, Manuel S. Rodriguez, Graham D. Kemp, Ronald T. HayAbstract:The ubiquitin-like protein SUMO-1 is conjugated to a variety of proteins including Ran GTPase-activating protein 1 (RanGAP1), IκBα, and PML. SUMO-1-modified proteins display altered subcellular targeting and/or stability. We have purified the SUMO-1-activating enzyme from human cells and shown that it contains two subunits of 38 and 72 kDa. Isolation of cDNAs for each subunit indicates that they are homologous to ubiquitin-activating enzymes and to the Saccharomyces cerevisiae enzymes responsible for conjugation of Smt3p and Rub-1p. In vitro, recombinant SAE1/SAE2 (SUMO-1-activating enzyme) was capable of catalyzing the ATP-dependent formation of a thioester linkage between SUMO-1 and SAE2. The addition of the SUMO-1-conjugating enzyme Ubch9 resulted in efficient transfer of the thioester-linked SUMO-1 from SAE2 to Ubch9. In the presence of SAE1/SAE2, Ubch9, and ATP, SUMO-1 was efficiently conjugated to the protein substrate IκBα. As SAE1/SAE2, Ubch9, SUMO-1, and IκBα are all homogeneous, recombinant proteins, it appears that SUMO-1 conjugation of IκBα in vitrodoes not require the equivalent of an E3 ubiquitin protein ligase activity.
Ellis Jaffray - One of the best experts on this subject based on the ideXlab platform.
-
Unique binding interactions among Ubc9, SUMO and RanBP2 reveal a mechanism for SUMO paralog selection
Nature structural & molecular biology, 2004Co-Authors: Michael H. Tatham, Yuan Chen, Ellis Jaffray, Suhkmann Kim, Jing Song, Ronald T. HayAbstract:The conjugation of small ubiquitin-like modifiers SUMO-1, SUMO-2 and SUMO-3 onto target proteins requires the concerted action of the specific E1-activating enzyme SAE1/SAE2, the E2-conjugating enzyme Ubc9, and an E3-like SUMO ligase. NMR chemical shift perturbation was used to identify the surface of Ubc9 that interacts with the SUMO ligase RanBP2. Unlike known ubiquitin E2-E3 interactions, RanBP2 binds to the beta-sheet of Ubc9. Mutational disruption of Ubc9-RanBP2 binding affected SUMO-2 but not SUMO-1 conjugation to Sp100 and to a newly identified RanBP2 substrate, PML. RanBP2 contains a binding site specific for SUMO-1 but not SUMO-2, indicating that a Ubc9-SUMO-1 thioester could be recruited to RanBP2 via SUMO-1 in the absence of strong binding between Ubc9 and RanBP2. Thus we show that E2-E3 interactions are not conserved across the ubiquitin-like protein superfamily and identify a RanBP2-dependent mechanism for SUMO paralog-specific conjugation.
-
polymeric chains of sumo 2 and sumo 3 are conjugated to protein substrates by SAE1 sae2 and ubc9
Journal of Biological Chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
-
Polymeric chains of SUMO-2 and SUMO-3 are conjugated to protein substrates by SAE1/SAE2 and Ubc9
The Journal of biological chemistry, 2001Co-Authors: Michael H. Tatham, Joana M. P. Desterro, Ellis Jaffray, Owen A. Vaughan, Catherine H. Botting, James H. Naismith, Ronald T. HayAbstract:Conjugation of the small ubiquitin-like modifier SUMO-1/SMT3C/Sentrin-1 to proteins in vitro is dependent on a heterodimeric E1 (SAE1/SAE2) and an E2 (Ubc9). Although SUMO-2/SMT3A/Sentrin-3 and SUMO-3/SMT3B/Sentrin-2 share 50% sequence identity with SUMO-1, they are functionally distinct. Inspection of the SUMO-2 and SUMO-3 sequences indicates that they both contain the sequence ψKXE, which represents the consensus SUMO modification site. As a consequence SAE1/SAE2 and Ubc9 catalyze the formation of polymeric chains of SUMO-2 and SUMO-3 on protein substrates in vitro, and SUMO-2 chains are detectedin vivo. The ability to form polymeric chains is not shared by SUMO-1, and although all SUMO species use the same conjugation machinery, modification by SUMO-1 and SUMO-2/-3 may have distinct functional consequences.
