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Jack F. Kirsch – One of the best experts on this subject based on the ideXlab platform.
S-methylmethionine is both a substrate and an inactivator of 1-Aminocyclopropane-1-Carboxylate Synthase.Archives of Biochemistry and Biophysics, 2004Co-Authors: Saehee Ko, Andrew C. Eliot, Jack F. KirschAbstract:
Abstract S-methyl- l –methionine (SMM) is ubiquitous in the tissues of flowering plants, but its precise function remains unknown. It is both a substrate and an inhibitor of the pyridoxal 5′-phosphate–dependent enzyme 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase, due to its structural similarity to the natural substrate of this enzyme, S-adenosyl- l –methionine. In the reaction with ACC Synthase, SMM can either be transaminated to yield 4-dimethylsulfonium-2-oxobutyrate; converted to α-ketobutyrate, ammonia, and dimethylsulfide; or inactivate the enzyme covalently after elimination of dimethylsulfide. These results suggest a previously unrecognized role for SMM in the regulation of ACC Synthase activity in plants.
Structure of 1-Aminocyclopropane-1-Carboxylate Synthase in complex with an amino-oxy analogue of the substrate: implications for substrate binding.Biochimica et Biophysica Acta, 2003Co-Authors: Guido Capitani, Jack F. Kirsch, Heinz Gut, Andrew C. Eliot, Radii M. Khomutov, Markus G GrutterAbstract:
Abstract The crystal structure of 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase in complex with the substrate analogue [2-(amino-oxy)ethyl](5′-deoxyadenosin-5′-yl)(methyl)sulfonium (AMA) was determined at 2.01-A resolution. The crystallographic results show that a covalent adduct (oxime) is formed between AMA (an amino-oxy analogue of the natural substrate S -adenosyl- l –methionine (SAM)) and the pyridoxal 5′-phosphate (PLP) cofactor of ACC Synthase. The oxime formation is supported by spectroscopic data. The ACC Synthase–AMA structure provides reliable and detailed information on the binding mode of the natural substrate of ACC Synthase and complements previous structural and functional work on this enzyme.
modulation of the internal aldimine pka s of 1 aminocyclopropane 1 carboxylate Synthase and aspartate aminotransferase by specific active site residuesBiochemistry, 2002Co-Authors: Andrew C. Eliot, Jack F. KirschAbstract:
The active sites of the homologous pyridoxal phosphate– (PLP-) dependent enzymes 1 -aminocyclopropane- I –carboxylate (ACC) Synthase and aspartate aminotransferase (AATase) are almost entirely conserved, yet the pK a ‘s ofthe two internal aldimines are 9.3 and 7.0, respectively, to complement the substrate pK a ‘s (S-adenosylmethionine pK a = 7.8 and aspartate pK a = 9.9). This complementation is required for maximum enzymatic activity in the physiological pH range. The most prominent structural difference in the active site is that Ile232 of ACC Synthase is replaced by alanine in AATase. The I232A mutation was introduced into ACC Synthase with a resulting 1.1 unit decrease (from 9.3 to 8.2) in the aldimine pK a , thus identifying Ile232 as a major determinant of the high pK a of ACC Synthase. The mutation also resulted in reduced k c a t (0.5 vs 11 s – 1 ) and k c a t /K m values (5.0 x 10 4 vs 1.2 x 10 6 M – 1 s – 1 ). The effect of the mutation is interpreted as the result of shortening of the Tyr233-PLP hydrogen bond. Addition of the Y233F mutation to the I232A ACC Synthase to generate the double mutant I232A/Y233F raised the pK a from 8.2 to 8.8, because the Y233F mutation eliminates the hydrogen bond between that residue and PLP. The introduction of the retro mutation A224I into AATase raised the aldimine pK a of that enzyme from 6.96 to 7.16 and resulted in a decrease in single-turnover k m a x (108 vs 900 s – 1 for aspartate) and k m a x /K m a p p (7.5 x 10 4 vs 3.8 x 10 5 M – 1 s – 1 ) values. The distance from the pyridine nitrogen of the cofactor to a conserved aspartate residue is 2.6 A in AATase and 3.8 A in ACC Synthase. The D230E mutation introduced into ACC Synthase to close this distance increases the aldimine pK a from 9.3 to 10.0, as would be predicted from a shortened hydrogen bond.
Athanasios Theologis – One of the best experts on this subject based on the ideXlab platform.
recessive and dominant mutations in the ethylene biosynthetic gene acs5 of arabidopsis confer cytokinin insensitivity and ethylene overproduction respectivelyProceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: John P Vogel, Athanasios Theologis, Keith Woeste, Joseph J KieberAbstract:
We identified a set of cytokinin-insensitive mutants by using a screen based on the ethylene-mediated triple response observed after treatment with low levels of cytokinins. One group of these mutants disrupts ACS5, a member of the Arabidopsis gene family that encodes 1-Aminocyclopropane-1-Carboxylate Synthase, the first enzyme in ethylene biosynthesis. The ACS5 isoform is mainly responsible for the sustained rise in ethylene biosynthesis observed in response to low levels of cytokinin and appears to be regulated primarily by a posttranscriptional mechanism. Furthermore, the dominant ethylene-overproducing mutant eto2 was found to be the result of an alteration of the carboxy terminus of ACS5, suggesting that this domain acts as a negative regulator of ACS5 function.
Random mutagenesis of 1-Aminocyclopropane-1-Carboxylate Synthase: a key enzyme in ethylene biosynthesis.Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Alice S. Tarun, J. S. Lee, Athanasios TheologisAbstract:
1-Aminocyclopropane-1-Carboxylate Synthase (ACC Synthase, EC 4.4.1. 14) catalyzes the rate-limiting step in the ethylene biosynthetic pathway in plants. To determine the amino acid residues critical for the structure and function of this enzyme, the tomato Le-ACS2 isoenzyme has been subjected to both site-directed and PCR random mutagenesis. Mutant ACC Synthases with reduced enzyme activity have been selected by using a genetic screen based on the functional complementation of an Escherichia coli Ile auxotroph that has been engineered to express ACC deaminase from Pseudomonas sp. The DNA sequence of almost 1,000 clones has been determined, and 334 single missense mutations have been selected for analysis. We have identified three classes of mutants based on their activity and expression in E. coli. Class I and II mutants have the same level of protein expression as the wild type, but their enzyme activity is reduced to 0-5% and 5-50%, respectively. Class III mutants have neither activity nor detectable protein expression. The inactive mutations are clustered in regions that are highly conserved among various ACC Synthases. This library of mutants will facilitate the elucidation of structure-function relationships of this regulatory enzyme.
The Plant journal : for cell and molecular biology, 1996Co-Authors: Xiaowu Liang, N F Shen, Athanasios TheologisAbstract:
Summary In Arabidopsis thaliana, 1-Aminocyclopropane-1-Carboxylate Synthase (ACS) is encoded by a multigene family consisting of at least five members whose expression is induced by hormones, developmental signals, and protein synthesis inhibition. Li+, known to interfere with the phosphoinositide (PI) second messenger system by inhibiting the activity of inositol–phosphate phosphatases, is one of the strongest inducers of ACC Synthase activity in plants. Treatment of etiolated Arabidopsis seedlings with LiCl results in a rapid induction of the ACS5 gene. Also, LiCl represses the cycloheximide (CHX)-induced accumulation of the ACS2 mRNA. The effects of Li+ on the expression of ACS5 and ACS2 are specific, dose-dependent, and can be reversed by Ca2+ and mimicked by the protein kinase inhibitor K-252a. The results suggest that the regulation of some ACS genes by various inducers may involve protein kinase activity, which in turn may be controlled through an inositol 1,4,5-triphosphate (IP3)-mediated Ca2+ mobilization. Since plants contain no Li+, the cation appears to unmask pre-existing biochemical capacity that may be utilized by various unknown transducers during plant growth and development.
Shang Fa Yang – One of the best experts on this subject based on the ideXlab platform.
Identification of two chilling-regulated 1-Aminocyclopropane-1-Carboxylate Synthase genes from citrus (Citrus sinensis Osbeck) fruitPlant molecular biology, 1999Co-Authors: Wai Shing Wong, Shain Dow Kung, Wen Ning, Shang Fa YangAbstract:
Diurnal change in the temperature below or above 12.5 °C hastens the degreening of citrus peel and elicits the phytohormone ethylene production in citrus fruit. Ethylene triggers the degradation of chlorophyll and synthesis of carotenoids in citrus peel. To investigate if ethylene is required for the degreening of citrus peel elicited by low temperatures, we studied the chilling-regulated gene expression of ACC Synthase, one of the key enzymes catalyzing ethylene biosynthesis. We isolated and characterized a chilling-inducible 1-Aminocyclopropane-1-Carboxylate Synthase (ACC Synthase) gene, CS-ACS1, and a chilling-repressible gene, CS-ACS2, from citrus peel. The CS-ACS1 transcript 1.7 kb in length encodes a polypeptide of 483 amino acids (Mr 54 115, pI 6.63), whereas the CS-ACS2 transcript of 1.8 kb encodes a polypeptide of 477 amino acids (Mr 53 291, pI 6.72). Both genes showed a rapid but transient induction (within 2.4 h) of transcripts upon rewarming after the chilling (4 °C) treatment. After 24 h of incubation at room temperature, CS-ACS1 mRNA diminished to an undetectable level, whereas the CS-ACS2 mRNA regained its basal level of expression attained prior to the chilling treatment. Chilling-induced ethylene production and ACC accumulation were also observed upon rewarming. Both genes were also induced by the wound stress (excision). The protein synthesis inhibitor cycloheximide super-enhances the accumulation of both ACS transcripts at room temperature. Molecular analysis of the 3.3 kb genomic DNA of CS-ACS1 revealed that this gene consists of three introns and four exons. The intron 3 is exceptionally large (1.2 kb) and shares significant homology with mitochondrial DNA, supporting the intron-late theory.
Differential induction of seven 1-Aminocyclopropane-1-Carboxylate Synthase genes by elicitor in suspension cultures of tomato (Lycopersicon esculentum)Plant Molecular Biology, 1997Co-Authors: Jürg H. Oetiker, David C. Olson, Oi Yin Shiu, Shang Fa YangAbstract:
The key enzyme of ethylene biosynthesis, ACC Synthase, is encoded by a multigene family. We describe three new DNA sequences encoding members of the ACC Synthase family of the tomato. One of these sequences encodes a novel ACC Synthase, LE-ACS6, which is phylogenetically related to the ACC Synthases LE-ACS1A and LE-ACS1B. Gene-specific probes for seven tomato ACC Synthase genes were prepared. They were used for RNase protection assays to study the accumulation of ACC Synthase transcripts in suspension-cultured tomato cells after the addition of an elicitor. The ACC Synthase genes LE-ACS2, LE-ACS5 and LE-ACS6 were strongly induced by the elicitor. In contrast, the genes LE-ACS1B, LE-ACS3 and LE-ACS4 were constitutively expressed and LE-ACS1B was present at all times at a particularly high level. Thus, there are two groups of ACC Synthase transcripts expressed in these cells, either elicitor-induced or constitutive. A transcript of LE-ACS1A was not detected. Despite the presence of LE-ACS1B, LE-ACS2, LE-ACS3, LE-ACS4 and LE-ACS5, there was only little ethylene produced in the absence of the elicitor. Increased ethylene production is usually correlated with the accumulation of ACC Synthase transcripts, indicating that ethylene production is controlled via the transcriptional activation of ACC Synthase genes. However, the abundance of several ACC Synthase mRNAs studied was not strictly correlated with the rate of elicitor-induced ethylene production. Our data provide evidence that the activity of these ACC Synthases may not solely be controlled by the transcriptional activation of ACC Synthase genes.
auxin induces three genes encoding 1 aminocyclopropane 1 carboxylate Synthase in mung bean hypocotylsJournal of Plant Physiology, 1997Co-Authors: Alan D Campbell, Takaya Moriguchi, Ho Chul Yi, Shang Fa YangAbstract:
Summary By screening a cDNA library of auxin-treated mung bean ( Vigna radiata L.) hypocotyls, we have isolated two full-length cDNA clones, pVR-ACS6 and pVR-ACS7, for 1-Aminocyclopropane-1-Carboxylate (ACQ Synthase, the rate-limiting enzyme in the ethylene biosynthetic pathway. While pVR-ACS6 corresponds to the previously identified PCR fragment pMBAl, pVR-ACS7 is a new cDNA clone. pVR-ACS6 is 1867bp long encoding 472 amino acids (Mr = 53.6 kDa), and pVR-ACS7 is a 1840 bp clone encoding 468 amino acids (Mr = 53.1 kDa). The coding regions of pVR-ACS6 and pVR-ACS7 share 81 and 88 % identity at nucleotide and amino acid levels, respectively. Genomic Southern blot analyses suggest the existence of only one copy of ACS6 and ACS7 genes in the mung bean genome. Previously, it was reported that mung bean ACC Synthase cDNA clone (pAIM-1) representing ACS1 gene was expressed following auxin treatment. Northern blot analyses were carried out to compare the magnitudes and induction kinetics of the expression of the three genes, ACS1, ACS6 and ACS7 whose expressions are induced by auxin (100 µM IAA) in hypocotyls. Although all three genes are expressed in response to auxin treatment, the level of ACS1 transcript is lower than those of ACS6 and ACS7 transcripts during the entire period of auxin treatment. ACS6 and ACS7 are specifically induced by auxin, while ACS1 is induced by cycloheximide, and to lesser extent by excision and auxin treatment. A comparison of deduced amino acid sequences among auxin-induced ACC Synthases reveals that these enzymes share a high degree of homology (65–75 %) to VR-ACS6 and VR-ACS7 polypeptides, but only about 50% to VR-ACS1 polypeptide. These results indicate that ACC Synthase is encoded by a multigene family and expression of these genes is differentially regulated by auxin in mung bean hypocotyl tissue.
Hitoshi Mori – One of the best experts on this subject based on the ideXlab platform.
Rapid and transient expression of 1-Aminocyclopropane-1-Carboxylate Synthase isogenes by touch and wound stimuli in tomatoPlant & cell physiology, 1999Co-Authors: Miho Tatsuki, Hitoshi MoriAbstract:
Touch stimuli induce ethylene production from 1-aminocyclopropane-1-carboxylic acid (ACC) in various plant species. We attempted to determine which ACC Synthase (ACS) isogenes play a role in this phenomenon. We isolated cDNA clones (LE-ACS1A, 1B, 2, 3, 4 and 6) for ACC Synthase isogenes from tomato, and their expressions were examined. Touch stimulation of tomato seedlings and fruits led to a large increase in the levels of LE-ACS6 and LE-ACS1A mRNA transcripts. The expressions of LE-ACS6 and LE-ACS1A isogenes increased within 10 min after touch, and mRNAs for both genes disappeared by 2 h. Thus, their expressions are transient. Wounding of tomato leaves and fruits also gave rise to transient expressions of LE-ACS6 and LE-ACS1A. The mRNA of the LE-ACS2 gene, a wound-inducible gene, was detected after 2 h in wounded tissues, but not in touched tissues. The results clearly indicate that the two isogenes, LE-ACS6 and LE-ACS1A, sense only touch, contact or pressure, and that another isogene, LE-ACS2, requires severe cell damage for its expression.
VR-ACS6 is an auxin-inducible 1-Aminocyclopropane-1-Carboxylate Synthase gene in mungbean (Vigna radiata).Plant & cell physiology, 1997Co-Authors: In Sun Yoon, Hitoshi Mori, Jeong Hoe Kim, Bin G. Kang, Hidemasa ImasekiAbstract:
We have isolated four cDNA clones of ACC Synthase from etiolated mungbean seedlings treated with auxin. pVR-ACS2, pVR-ACS3 and pVR-ACS6 contained the same sequences as the previously reported DNA fragments, pMAC2, pMAC3 (Botella et al. 1992b) and pMBA1 (Kim et al. 1992), respectively. pVR-ACS1 was identical with pAIM-1 (Botella et al. 1992a). VR-ACS6 was specifically induced in response to the auxin signal. The IAA-induction of VR-ACS6 was very rapid (within 30 min) and insensitive to cycloheximide treatment at concentrations up to 100 microM. Significant accumulation of VR-ACS6 mRNA was detected at 1 microM IAA. The IAA-induced expression of VR-ACS6 was suppressed by ABA and ethylene, but enhanced by BA. These characteristics of VR-ACS6 expression were well correlated with the physiological data of auxin-induced ethylene production in mungbean hypocotyls. VR-ACS1 was strongly induced by cycloheximide, but was found to be not auxin-specific. Inhibitors of either ethylene biosynthesis (AOA) or action (NBD) increased the basal level of VR-ACS1 mRNA.
Plant physiology, 1995Co-Authors: T Miki, Hiroki Nakagawa, Mitsuaki Yamamoto, N Ogura, Hitoshi Mori, H Imaseki, Takahide SatoAbstract:
Ethylene is a plant hormone that has an essential role in fruit ripening (Yang and Hoffman, 1984; Kende, 1993). ACC Synthase (S-adenosyl-L-methionine methylethioadenosine-lyase, EC 184.108.40.206), which is encoded by a multigene family, plays a regulatory role in ethylene production. Severa1 genes for ACC Synthase have been isolated from tomato (Rottmann et al., 1991), mung bean (Botella et al., 1992, 19931, winter squash (Nakajima et al., 1990; Nakagawa et al., 1991), and Arabidopsis (Liang et al., 1992; Van Der Straeten et al., 1992). Two ACC Synthase genes (LE-ACS2 and LE-ACS4, which are identified as a wounding and a ripening inducing gene, respectively) are expressed during ripening of tomato fruits (Olson et al., 1991; Rottmann et al., 1991). An antisense RNA experiment with LEACS2 reduced the levels of mRNAs for LEACS2 and LEACS4 in tomato fruits and caused retardation of initiation of ripening of tomato fruits (Oeller et al., 1991). These results showed that wound-induced ACC Synthase also played an important role in the production of ethylene in tomato fruit during ripening. We isolated a cDNA (pMEACS1,2097 bp) for ACC Synthase from wounded mesocarp tissue of melon fruits (Cucumis melo L. cv AMS) (Table I). The polypeptide derived from the cDNA in Escherichiu coli had ACC Synthase activity. Sequence analysis of this cDNA revealed the presente of an open reading frame of 493 amino acids. This polypeptide contained seven sequences that were conserved among other ACC Synthases. pMEACSl showed high homology at the amino acid and nucleotide levels to wound-induced ACC Synthase from squash (Nakajima et al., 1990; Sato et al., 1991). RNA blot analysis showed that the level of mRNA for the gene increased in the mesocarp tissue of melon fruits after wounding and also during ripening. Since we could detect cDNA only for MEACSl ACC Synthase in a PCR experiment with the mRNA from mesocarp tissue of ripe melon fruits, MEACSl should be the gene that is preferentially expressed during ripening of
Ning Ning Wang – One of the best experts on this subject based on the ideXlab platform.
negative feedback regulation of system 1 ethylene production by the tomato 1 aminocyclopropane 1 carboxylate Synthase 6 gene promoterPlant Science, 2008Co-Authors: Shihhsun Chang, Ning Ning Wang, Yee-yung CharngAbstract:
Abstract In tomato, two distinct ethylene production systems, the autoinhibitory (system-1) and the autocatalytic (system-2), operate sequentially during fruit development. LE-ACS6 has been shown to be negatively regulated by endogenous and exogenous ethylene, and was thought to be involved in system-1 ethylene biosynthesis. To investigate the mechanism of the autoinhibitory regulation of LE-ACS6, we isolated its 5′-flanking sequence and examined the expression of a chimeric LE-ACS6 promoter (−1293 to +25)::β-glucuronidase (GUS) fusion gene in transgenic tomato. According to computer-based prediction, the 1.3 kb promoter sequence contains putative cis-elements required for ethylene, auxin, abscisic acid (ABA), and wounding responses. In transgenic tomato, the cloned promoter was sufficient to modulate GUS in response to exogenous ethylene in a tissue-specific manner, and with similar transcript levels to the endogenous LE-ACS6. Histochemical staining illustrated GUS activity in the cotyledons, hypocotyls and roots of seedlings as well as in flowers, leaves, and fruits. Among all tested tissues, GUS activity was highest at the immature green stage in fruit. In flowers, GUS activity peaked at anthesis and decreased during senescence. Auxin but not ABA increased GUS activity and LE-ACS6 transcript levels in seedlings. Wounding significantly increased GUS activity and LE-ACS6 transcripts in the fruit pericarp but not in the leaves. Based on these results, we conclude that the autoinhibition of LE-ACS6 expression is mainly under the transcriptional control of the promoter region of the gene.
Auto-regulation of the promoter activities of Arabidopsis 1-Aminocyclopropane-1-Carboxylate Synthase genes AtACS4, AtACS5, and AtACS7 in response to different plant hormones §Plant Science, 2008Co-Authors: Xuenu Tang, Li Chang, Guiqin Liu, Ning Ning WangAbstract:
Abstract 1-Aminocyclopropane-1-Carboxylate Synthase (ACC Synthase, ACS) ( S -adenosyl- l –methionine methylthioadenosine-lyase; EC 220.127.116.11), the key enzyme for ethylene biosynthesis, is subjected to positive or negative feedback regulation by the hormone itself. We have previously described, aided by promoter-GUS (β-glucuronidase) reporter approach, that among members of the multigene family of Arabidopsis ACC Synthase, AtACS4 , AtACS5 and AtACS7 genes exhibit different responses to exogenous ethylene treatment. Here we report differences in their developmental expression profiles and hormone responses between wild type and etr1-1 mutants. It was found that these three ACS members were all actively expressed in 2-week-old wild type light-grown seedlings but exhibited different profiles in etr1-1 mutant. The expression of AtACS7::GUS during the entire life cycle of Arabidopsis was greatly suppressed in etr1-1 mutant while the expressions of AtACS4::GUS and AtACS5::GUS exhibited no significant changes. The effects of seven major plant hormones and ethylene precursor ACC on the promoter activities of these three ACS genes were studied by fluorometric GUS activity assay. It was found that exogenous treatment of IAA, ACC, ABA or JA increased the promoter activity of AtACS4 in the wild type background but the promotions by ACC, ABA and JA were almost absent in the etr1-1 background. Block of the ethylene signaling also abolished both the IAA- and the ABA-induced AtACS5::GUS expression. The ACS7 promoter was responsive to six members of the eight hormones (GA 3 , ACC, ABA, JA, SA and BR), among which, the increases by GA 3 , ACC, SA and BR were abolished in the etr1-1 mutant. Based on these results, the role of ethylene signaling in regulating responses of AtACS4 , AtACS5 and AtACS7 to different hormones was discussed.
Structural analysis of the promoter of tomato 1-Aminocyclopropane-1-Carboxylate Synthase 6 gene ( Le-ACS6 )Chinese Science Bulletin, 2007Co-Authors: Jingyu Lin, Rong Fan, Xiao-rong Wan, Yee-yung Charng, Ning Ning WangAbstract:
Ethylene plays an important role in the regulation of many growth and developmental processes of higher plants. In tomato, Le-ACS6, a member of the ACC Synthase multigene family involved in system 1 ethylene biosynthesis during fruit ripening, is subject to negative feedback regulation by ethylene. To identify the cis-elements that are responsible for the negative feedfeedback control, we established an in vitro transient assay system employing particle bombardment on mature-green tomato fruit pericarp to examine the expression of a luciferase (LUC) reporter gene driven by a 5′-serially deleted Le-ACS6 promoter. The results localized putative cis-elements required for negative ethylene-response between −347 and −266 upstream from the translational start site ATG. Several lines of stable transformation of the Le-ACS6 promoter and GUS reporter fusion gene containing internal deletion from −347 to −266 were generated. The expression pattern of the GUS reporter showed that removal of the nucleotides from −347 to −266 completely eliminated the response of the Le-ACS6 promoter to exogenous ethylene.