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Identification and characterization of Helicobacter pylori O‐acetylserine‐dependent cystathionine β‐synthase, a distinct member of the PLP‐II family
Author(s) -
Devi Suneeta,
Tarique Khaja Faisal,
Ali Mohammad Farhan,
Abdul Rehman Syed Arif,
Gourinath Samudrala
Publication year - 2019
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.14315
Subject(s) - cystathionine beta synthase , serine , biology , biochemistry , cysteine , active site , enzyme
Summary O‐acetylserine sulfhydrylase (OASS) and cystathionine β‐synthase (CBS) are members of the PLP‐II family, and involved in L‐cysteine production. OASS produces L‐cysteine via a de novo pathway while CBS participates in the reverse transsulfuration pathway. O‐acetylserine‐dependent CBS (OCBS) was previously identified as a new member of the PLP‐II family, which are predominantly seen in bacteria. The bacterium Helicobacter pylori possess only one OASS ( hp0107 ) gene and we showed that the protein coded by this gene actually functions as an OCBS and utilizes L‐homocysteine and O‐acetylserine (OAS) to produce cystathionine. Hp OCBS did not show CBS activity with the substrate L‐serine and required OAS exclusively. The Hp OCBS structure in complex with methionine showed a closed cleft state, explaining the initial mode of substrate binding. Sequence and structural analyses showed differences between the active sites of OCBS and CBS, and explain their different substrate preferences. We identified three hydrophobic residues near the active site of OCBS, corresponding to one serine and two tyrosine residues in CBSs. Mutational studies were performed on Hp OCBS and Saccharomyces cerevisiae CBS. A Sc CBS double mutant (Y158F/Y226V) did not display activity with L‐serine, indicating indispensability of these polar residues for selecting substrate L‐serine, however, did show activity with OAS.