Open AccessA novel mechanism of sulfur transfer catalyzed by O ‐acetylhomoserine sulfhydrylase in the methionine‐biosynthetic pathway of Wolinella succinogenes
Author(s) -
Tran Timothy H.,
Krishnamoorthy Kalyanaraman,
Begley Tadhg P.,
Ealick Steven E.
Publication year - 2011
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444911028010
Subject(s) - tetramer , chemistry , lyase , methionine , homotetramer , pyridoxal , cysteine , enzyme , active site , stereochemistry , dimer , biochemistry , amino acid , protein subunit , organic chemistry , gene
O ‐Acetylhomoserine sulfhydrylase (OAHS) is a pyridoxal 5′‐phosphate (PLP) dependent sulfide‐utilizing enzyme in the l ‐cysteine and l ‐methionine biosynthetic pathways of various enteric bacteria and fungi. OAHS catalyzes the conversion of O ‐acetylhomoserine to homocysteine using sulfide in a process known as direct sulfhydrylation. However, the source of the sulfur has not been identified and no structures of OAHS have been reported in the literature. Here, the crystal structure of Wolinella succinogenes OAHS (MetY) determined at 2.2 Å resolution is reported. MetY crystallized in space group C 2 with two monomers in the asymmetric unit. Size‐exclusion chromatography, dynamic light scattering and crystal packing indicate that the biological unit is a tetramer in solution. This is further supported by the crystal structure, in which a tetramer is formed using a combination of noncrystallographic and crystallographic twofold axes. A search for structurally homologous proteins revealed that MetY has the same fold as cystathionine γ‐lyase and methionine γ‐lyase. The active sites of these enzymes, which are also PLP‐dependent, share a high degree of structural similarity, suggesting that MetY belongs to the γ‐elimination subclass of the Cys/Met metabolism PLP‐dependent family of enzymes. The structure of MetY, together with biochemical data, provides insight into the mechanism of sulfur transfer to a small molecule via a protein thiocarboxylate intermediate.