7C35

Crystal structure of M96A mutant of O-acetyl-L-serine sulfhydrylase from Haemophilus influenzae

Summary for 7C35

• Entry DOI: 10.2210/pdb7c35/pdb
• Descriptor: Cysteine synthase (2 entities in total)
• Functional Keywords: plp dependent enzyme, cysteine metabolizing enzyme, o acetyl transferase enzyme, transferase
• Biological source: Haemophilus influenzae Rd KW20
• Total number of polymer chains: 1
• Total formula weight: 37144.27

Authors

Abhishek, K.,Rahisuddin, R.,Kumaran, S. (deposition date: 2020-05-11, release date: 2020-06-17, Last modification date: 2023-11-29)

Primary citation

Kaushik, A.,Rahisuddin, R.,Saini, N.,Singh, R.P.,Kaur, R.,Koul, S.,Kumaran, S.
Molecular mechanism of selective substrate engagement and inhibitor disengagement of cysteine synthase.
J.Biol.Chem., 296:100041-100041, 2020

PubMed Abstract: O-acetyl serine sulfhydrylase (OASS), referred to as cysteine synthase (CS), synthesizes cysteine from O-acetyl serine (OAS) and sulfur in bacteria and plants. The inherent challenge for CS is to overcome 4 to 6 log-folds stronger affinity for its natural inhibitor, serine acetyltransferase (SAT), as compared with its affinity for substrate, OAS. Our recent study showed that CS employs a novel competitive-allosteric mechanism to selectively recruit its substrate in the presence of natural inhibitor. In this study, we trace the molecular features that control selective substrate recruitment. To generalize our findings, we used CS from three different bacteria (Haemophilus, Salmonella, and Mycobacterium) as our model systems and analyzed structural and substrate-binding features of wild-type CS and its ∼13 mutants. Results show that CS uses a noncatalytic residue, M120, located 20 Å away from the reaction center, to discriminate in favor of substrate. M120A and background mutants display significantly reduced substrate binding, catalytic efficiency, and inhibitor binding. Results shows that M120 favors the substrate binding by selectively enhancing the affinity for the substrate and disengaging the inhibitor by 20 to 286 and 5- to 3-folds, respectively. Together, M120 confers a net discriminative force in favor of substrate by 100- to 858-folds.

PubMed: 33162395
DOI: 10.1074/jbc.RA120.014490

Experimental method

X-RAY DIFFRACTION (2.1 Å)