Solution structure and dynamics of an open beta-sheet, glycolytic enzyme, monomeric 23.7 kDa phosphoglycerate mutase from Schizosaccharomyces pombe

The structure and backbone dynamics of a double labelled (N-15,C-13) monome ric, 23.7 kD phosphoglycerate mutase (PGAM) from Schizosaccharomyces pombe have been investigated in solution using NMR spectroscopy. A set of 3125 NO E-derived distance restraints, 148 restraints representing inferred hydroge n bonds and 149 values of (3)J(HNH alpha) were used in the structure calcul ation. The mean rmsd from the average structure for all backbone atoms from residues 6-205 in the best 21 calculated structures was 0.59 Angstrom. The core of the enzyme includes an open, twisted, six-stranded beta -sheet fla nked by four alpha -helices and a short 3(10)-helix. An additional smaller domain contains two short antiparallel beta -strands and a further pair of alpha -helices. The C-alpha atoms of the S. pombe PGAM may be superimposed on their equivalents in one of the four identical subunits of Saccharomyces cerevisiae PGAM with an rmsd of 1.34 Angstrom (0.92 Angstrom if only the ( beta -sheet is considered). Small differences between the two structures ar e attributable partly to the deletion in the S. pombe sequence of a 25 resi due loop involved in stabilising the S, cereviseiae tetramer. Analysis of N -15 relaxation parameters indicates that PGAM tumbles isotropically with a rotational correlation time of 8.7 ns and displays a range of dynamic featu res. Of 178 residues analysed, only 77 could be fitted without invoking ter ms for fast internal motion or chemical exchange, and out of the remainder, 77 required a chemical exchange term. Significantly, 46 of the slowly exch anging (milli- to microsecond) residues lie in helices, and these account f or two-thirds of all analysed helix residues. On the contrary, only one P-s heet residue required an exchange term. In contrast to other analyses of ba ckbone dynamics reported previously, residues in slow exchange appeared to correlate with architectural features of the enzyme rather than congregatin g close to ligand binding sites. (C) 2001 Academic Press.