Download MendeleySecond-Shell Amino Acid R266 Helps Determine N -Succinylamino Acid Racemase Reaction Specificity in Promiscuous N -Succinylamino Acid Racemase/ o -Succinylbenzoate Synthase Enzymes.
Truong, D.P., Rousseau, S., Machala, B.W., Huddleston, J.P., Zhu, M., Hull, K.G., Romo, D., Raushel, F.M., Sacchettini, J.C., Glasner, M.E.(2021) Biochemistry 60: 3829-3840
- PubMed: 34845903
- DOI: https://doi.org/10.1021/acs.biochem.1c00627
- Primary Citation of Related Structures:
7S8W - PubMed Abstract:
Catalytic promiscuity is the coincidental ability to catalyze nonbiological reactions in the same active site as the native biological reaction. Several lines of evidence show that catalytic promiscuity plays a role in the evolution of new enzyme functions. Thus, studying catalytic promiscuity can help identify structural features that predispose an enzyme to evolve new functions. This study identifies a potentially preadaptive residue in a promiscuous N -succinylamino acid racemase/ o -succinylbenzoate synthase (NSAR/OSBS) enzyme from Amycolatopsis sp. T-1-60. This enzyme belongs to a branch of the OSBS family which includes many catalytically promiscuous NSAR/OSBS enzymes. R266 is conserved in all members of the NSAR/OSBS subfamily. However, the homologous position is usually hydrophobic in other OSBS subfamilies, whose enzymes lack NSAR activity. The second-shell amino acid R266 is close to the catalytic acid/base K263, but it does not contact the substrate, suggesting that R266 could affect the catalytic mechanism. Mutating R266 to glutamine in Amycolatopsis NSAR/OSBS profoundly reduces NSAR activity but moderately reduces OSBS activity. This is due to a 1000-fold decrease in the rate of proton exchange between the substrate and the general acid/base catalyst K263. This mutation is less deleterious for the OSBS reaction because K263 forms a cation-π interaction with the OSBS substrate and/or the intermediate, rather than acting as a general acid/base catalyst. Together, the data explain how R266 contributes to NSAR reaction specificity and was likely an essential preadaptation for the evolution of NSAR activity.
Organizational Affiliation:
Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, Texas 77843-2128, United States.
