PMID: 25336647
McCorvie TJ, Kopec J, Hyung SJ, Fitzpatrick F, Feng X, Termine D, Strain-Damerell C, Vollmar M, Fleming J, Janz JM, Bulawa C, Yue WW
Inter-Domain Communication Of Human Cystathionine Beta Synthase: Structural Basis Of S-Adenosyl-L-Methionine Activation.
J Biol Chem. 2014 Oct 21. pii: jbc.M114.610782.
Cystathionine beta-synthase (CBS) is a key enzyme in sulphur metabolism, and its inherited deficiency causes homocystinuria. Mammalian CBS is modulated by the binding of S-adenosyl-L-methionine (SAM) to its regulatory domain, which activates its catalytic domain. To investigate the underlying mechanism, we performed x-ray crystallography, mutagenesis and mass-spectrometry (MS) on human CBS. The 1.7 A structure of a SAM-bound CBS regulatory domain shows one SAM molecule per monomer, at the interface between two constituent modules (CBS-1, CBS-2). SAM binding is accompanied by a reorientation between the two modules, relative to the SAM-free basal state, to form interactions with SAM via residues verified by mutagenesis to be important for SAM binding (Phe443, Asp444, Gln445 and Asp538) and for SAM-driven inter-domain communication (Phe443, Asp538). The observed structural change is further supported by ion mobility MS showing that as-purified CBS exists in two conformational populations which converged to one upon binding SAM. We therefore propose that SAM-induced conformational change alters the interface and arrangement between the catalytic and regulatory domains within the CBS oligomer, thereby increasing the accessibility of the enzyme active site for catalysis.