THE ROLE OF THE C-TERMINAL LYSINE IN THE HINGE BENDING MECHANISM OF YEAST PHOSPHOGLYCERATE KINASE

Treatment of yeast phosphoglycerate kinase (PGK) with trypsin results in a fourfold increase in the V-max of this enzyme, without affecting the K-m. This activation is shown to be due to the removal of the C-te rminal lysine residue. The C-terminal sequence folds back over the N-t erminal domain and contacts the extreme N-terminal sequence which fold s onto the C-terminal domain, thus making many of the inter-domain con tacts in this two domain protein. Previous studies have shown that thi s C-terminal region is important in mediating the conformational chang es required during catalysis by yeast PGK. Observation of the three-di mensional structure of this enzyme suggests that removal of the C-term inal lysine residue will strengthen the interaction between K5 and E41 3. This indicates that this salt bridge stabilises the enzyme in the h igher activity form, while the presence of K415 reduces the strength o f that interaction.