Investigation of the quaternary structure of Neurospora pyruvate kinase by cross-linking with bifunctional reagents: the effect of substrates and allosteric ligands

Abstract

Pyruvate kinase (EC 2.7.1.40) of Neurospora crassa, a tetramer composed of apparently identical subunits, was shown to be a dimer of dimers by interprotomeric cross-linking experiments in which bifunctional reagents were used. An analysis of the polyacrylamide gel profiles of the enzyme after cross-linking with glutaraldehyde, dimethyl suberimidate and dimethyl adipimidate shows that the extent of intersubunit cross-linking is influenced markedly by the ligand bound to the enzyme. Bifunctional cross-linking reagents with a shorter distance between the 2 functional groups form cross-links effectively in the unliganded enzyme. In the FDP[fructose-1,6-diphosphate]-pyruvate kinase complex, cross-linking was observed over longer distances compared with the unliganded enzyme. Covalent cross-linkers can be used as sensitive indicators of conformational changes induced in pyruvate kinase by substrates and allosteric ligands.