Inter-domain communication of human cystathionine β-synthase: structural basis of S-adenosyl-L-methionine activation

J Biol Chem. 2014 Dec 26;289(52):36018-30. doi: 10.1074/jbc.M114.610782. Epub 2014 Oct 21.


Cystathionine β-synthase (CBS) is a key enzyme in sulfur metabolism, and its inherited deficiency causes homocystinuria. Mammalian CBS is modulated by the binding of S-adenosyl-l-methionine (AdoMet) 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 Å structure of a AdoMet-bound CBS regulatory domain shows one AdoMet molecule per monomer, at the interface between two constituent modules (CBS-1, CBS-2). AdoMet binding is accompanied by a reorientation between the two modules, relative to the AdoMet-free basal state, to form interactions with AdoMet via residues verified by mutagenesis to be important for AdoMet binding (Phe(443), Asp(444), Gln(445), and Asp(538)) and for AdoMet-driven inter-domain communication (Phe(443), Asp(538)). 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 in the presence of AdoMet. We therefore propose that AdoMet-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.

Keywords: Activation; Allosteric Regulation; Conformational Change; Crystallography; Cystathionine β-Synthase; Enzyme; Mass Spectrometry (MS); S-adenosyl-l-methionine (AdoMet); SAM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalytic Domain
  • Crystallography, X-Ray
  • Cystathionine beta-Synthase / chemistry*
  • Humans
  • Hydrogen Bonding
  • Models, Molecular
  • Protein Binding
  • Protein Structure, Secondary
  • S-Adenosylmethionine / chemistry*


  • S-Adenosylmethionine
  • Cystathionine beta-Synthase

Associated data

  • PDB/4COO
  • PDB/4UUU