[NMR paper] Substrate and Cofactor Dynamics on Guanosine Monophosphate Reductase Probed by High Resolution Field Cycling 31P NMR Relaxometry.

[nmrlearner]

Substrate and Cofactor Dynamics on Guanosine Monophosphate Reductase Probed by High Resolution Field Cycling 31P NMR Relaxometry.

Related Articles Substrate and Cofactor Dynamics on Guanosine Monophosphate Reductase Probed by High Resolution Field Cycling 31P NMR Relaxometry.

J Biol Chem. 2016 Sep 9;

Authors: Rosenberg MM, Redfield AG, Roberts MF, Hedstrom L

Abstract
Guanosine-5'-monophosphate reductase (GMPR) catalyzes the reduction of GMP to IMP and ammonia with concomitant oxidation of NADPH. Here we investigated the structure and dynamics of enzyme-bound substrates and cofactors by measuring (31)P relaxation rates over a large magnetic field range using high-resolution field cycling NMR relaxometry. Surprisingly, these experiments reveal differences in the low field relaxation profiles for the monophosphate of GMP compared to IMP in their respective NADP(+) complexes. These complexes undergo partial reactions that mimic different steps in the overall catalytic cycle. The relaxation profiles indicate that the substrate monophosphates have distinct interactions in E·IMP·NADP(+) and E·GMP·NADP(+) complexes. These findings were not anticipated by x-ray crystal structures, which show identical interactions for the monophosphates of GMP and IMP in several inert complexes. In addition, these experiments indicate that the cofactor has more internal motion when bound with GMP. Lastly, the motions of the substrate and cofactor are coordinately regulated: the cofactor has faster local motions than GMP in the deamination complex but is more constrained than IMP in the complex leading to hydride transfer. These results show that field cycling can be used to investigate the dynamics of protein-bound ligands and provide new insights into how portions of the substrate remote from the site of chemical transformation promote catalysis.


PMID: 27613871 [PubMed - as supplied by publisher]



More...