title: S-adenosylmethionine stabilizes cystathionine beta-synthase and modulates redox capacity.
abstract: The transsulfuration pathway converts homocysteine to cysteine and represents the metabolic link between antioxidant and methylation metabolism. The first and committing step in this pathway is catalyzed by cystathionine beta-synthase (CBS), which is subject to complex regulation, including allosteric activation by the methyl donor, S-adenosylmethionine (AdoMet). In this study, we demonstrate that methionine restriction leads to a >10-fold decrease in CBS protein levels, and pulse proteolysis studies reveal that binding of AdoMet stabilizes the protein against degradation by approximately 12 kcal/mol. These observations predict that under pathological conditions where AdoMet levels are diminished, CBS, and therefore glutathione levels, will be reduced. Indeed, we demonstrate this to be the case in a mouse model for spontaneous steatohepatitis in which the gene for the MAT1A isoenzyme encoding AdoMet synthetase has been disrupted, and in human hepatocellular carcinoma, where MAT1A is silenced. Furthermore, diminished CBS levels are associated with reduced cell viability in hepatoma cells challenged with tert-butyl hydroperoxide. This study uncovers a mechanism by which CBS is allosterically activated by AdoMet under normal conditions but is destabilized under pathological conditions, for redirecting the metabolic flux toward methionine conservation. A mechanistic basis for the coordinate changes in redox and methylation metabolism that are a hallmark of several complex diseases is explained by these observations.
authors.affiliation: Redox Biology Center and Biochemistry Department, University of Nebraska, Lincoln, NE 68588-0664, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Prudova
authors.forename: Zachary
authors.initials: Z
authors.lastname: Bauman
authors.forename: Aaron
authors.initials: A
authors.lastname: Braun
authors.forename: Victor
authors.initials: V
authors.lastname: Vitvitsky
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
authors.forename: Ruma
authors.initials: R
authors.lastname: Banerjee
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000235:genetics; D002460:Cell Line; D003541:Cystathionine beta-Synthase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability; D005234:Fatty Liver / Q000201:enzymology / Q000235:genetics; D020868:Gene Silencing; D006801:Humans; D008113:Liver Neoplasms / Q000201:enzymology / Q000235:genetics; D008715:Methionine / Q000378:metabolism; D008716:Methionine Adenosyltransferase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010084:Oxidation-Reduction; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D012436:S-Adenosylmethionine; D008715:Methionine; C506577:MAT1A protein, human; C490703:Mat1a protein, mouse; D008716:Methionine Adenosyltransferase; D003541:Cystathionine beta-Synthase