Human cystathionine β-synthase (CBS) contains two classes of binding sites for S-adenosylmethionine (SAM): complex regulation of CBS activity and stability by SAM.
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| Abstract |
CBS (cystathionine β-synthase) is a multidomain tetrameric enzyme essential in the regulation of homocysteine metabolism, whose activity is enhanced by the allosteric regulator SAM (S-adenosylmethionine). Missense mutations in CBS are the major cause of inherited HCU (homocystinuria). In the present study we apply a novel approach based on a combination of calorimetric methods, functional assays and kinetic modelling to provide structural and energetic insight into the effects of SAM on the stability and activity of WT (wild-type) CBS and seven HCU-causing mutants. We found two sets of SAM-binding sites in the C-terminal regulatory domain with different structural and energetic features: a high affinity set of two sites, probably involved in kinetic stabilization of the regulatory domain, and a low affinity set of four sites, which are involved in the enzyme activation. We show that the regulatory domain displays a low kinetic stability in WT CBS, which is further decreased in many HCU-causing mutants. We propose that the SAM-induced stabilization may play a key role in modulating steady-state levels of WT and mutant CBS in vivo. Our strategy may be valuable for understanding ligand effects on proteins with a complex architecture and their role in human genetic diseases and for the development of novel pharmacological strategies.
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| Authors | Angel L Pey, Tomas Majtan, Jose M Sanchez-Ruiz, Jan P Kraus |
| Journal | The Biochemical journal (Biochem J) Vol. 449 Issue 1 Pg. 109-21 (Jan 01 2013) ISSN: 1470-8728 [Electronic] England |
| PMID | 22985361 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't) |
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