title: Regulation of homocysteine metabolism by Mycobacterium tuberculosis S-adenosylhomocysteine hydrolase.
abstract: Mycobacterium tuberculosis modulates expression of various metabolism-related genes to adapt in the adverse host environment. The gene coding for M. tuberculosis S-adenosylhomocysteine hydrolase (Mtb-SahH) is essential for optimal growth and the protein product is involved in intermediary metabolism. However, the relevance of SahH in mycobacterial physiology is unknown. In this study, we analyze the role of Mtb-SahH in regulating homocysteine concentration in surrogate host Mycobacterium smegmatis. Mtb-SahH catalyzes reversible hydrolysis of S-adenosylhomocysteine to homocysteine and adenosine and we demonstrate that the conserved His363 residue is critical for bi-directional catalysis. Mtb-SahH is regulated by serine/threonine phosphorylation of multiple residues by M. tuberculosis PknB. Major phosphorylation events occur at contiguous residues Thr219, Thr220 and Thr221, which make pivotal contacts with cofactor NAD⁺. Consequently, phosphorylation negatively modulates affinity of enzyme towards NAD⁺ as well as SAH-synthesis. Thr219, Thr220 and Thr221 are essential for enzyme activity, and therefore, responsible for SahH-mediated regulation of homocysteine.
authors.affiliation: CSIR-Institute of Genomics and Integrative Biology, Delhi-110007, India.
authors.forename: Anshika
authors.initials: A
authors.lastname: Singhal
authors.forename: Gunjan
authors.initials: G
authors.lastname: Arora
authors.forename: Andaleeb
authors.initials: A
authors.lastname: Sajid
authors.forename: Abhijit
authors.initials: A
authors.lastname: Maji
authors.forename: Ajay
authors.initials: A
authors.lastname: Bhat
authors.forename: Richa
authors.initials: R
authors.lastname: Virmani
authors.forename: Sandeep
authors.initials: S
authors.lastname: Upadhyay
authors.forename: Vinay K
authors.initials: VK
authors.lastname: Nandicoori
authors.forename: Shantanu
authors.initials: S
authors.lastname: Sengupta
authors.forename: Yogendra
authors.initials: Y
authors.lastname: Singh
mesh_terms: D043383:Adenosylhomocysteinase / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D006639:Histidine / Q000737:chemistry; D006710:Homocysteine / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D053858:Metabolic Networks and Pathways; D008958:Models, Molecular; D009161:Mycobacterium / Q000201:enzymology / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D010766:Phosphorylation; D011487:Protein Conformation; D015203:Reproducibility of Results
chemical_list: D006710:Homocysteine; D006639:Histidine; D043383:Adenosylhomocysteinase