1H, 15N and 13C backbone resonance assignments of the P146A variant of β-phosphoglucomutase from Lactococcus lactis in its substrate-free form

beta-Phosphoglucomutase (beta PGM) is a magnesium-dependent phosphoryl transfer enzyme that catalyses the reversible isomerisation of beta-glucose 1-phosphate and glucose 6-phosphate, via two phosphoryl transfer steps and a beta-glucose 1,6-bisphosphate intermediate. Substrate-free beta PGM is an essential component of the catalytic cycle and an understanding of its dynamics would present significant insights into beta PGM functionality, and enzyme catalysed phosphoryl transfer in general. Previously, 30 residues around the active site of substrate-free beta PGM(WT) were identified as undergoing extensive millisecond dynamics and were unassignable. Here we report H-1, N-15 and C-13 backbone resonance assignments of the P146A variant (beta PGM(P146A)) in its substrate-free form, where the K145-A146 peptide bond adopts a trans conformation in contrast to all crystal structures of beta PGM(WT), where the K145-P146 peptide bond is cis. In beta PGM(P146A) millisecond dynamics are suppressed for all but 17 residues, allowing 92% of backbone resonances to be assigned. Secondary structure predictions using TALOS-N reflect beta PGM crystal structures, and a chemical shift comparison between substrate-free beta PGM(P146A) and beta PGM(WT) confirms that the solution conformations are very similar, except for the D137-A147 loop. Hence, the isomerisation state of the 145-146 peptide bond has little effect on structure but the cis conformation triggers millisecond dynamics in the hinge (V12-T16), the nucleophile (D8) and residues that coordinate the transferring phosphate group (D8 and S114-S116), and the D137-A147 loop (V141-A142 and K145). These millisecond dynamics occur in addition to those for residues involved in coordinating the catalytic Mg-II ion and the L44-L53 loop responsible for substrate discrimination.