Abstract

Saccharomyces cerevisiae phosphoenolpyruvate (PEP) carboxykinase catalyzes the reversible formation of oxaloacetate and adenosine triphosphate from PEP, adenosine diphosphate and carbon dioxide, and uses Mn2+ as the activating metal ion. Comparison with the crystalline structure of homologous Escherichia coli PEP carboxykinase [Tari et al. (1997) Nature Struct. Biol. 4, 990-994] shows that Lys213 is one of the ligands to Mn2+ at the enzyme active site. Coordination of Mn2+ to a lysyl residue is not common and suggests a low pKa value for the ε-NH 2 group of Lys213. In this work, we evaluate the role of neighboring Phe216 in contributing to provide a low polarity microenvironment suitable to keep the ε-NH2 of Lys213 in the unprotonated form. Mutation Phe216Tyr shows that the introduction of a hydroxyl group in the lateral chain of the residue produces a substantial loss in the enzyme affinity for Mn2+, suggesting an increase of the pKa of Lys213. In agreement with this interpretation, theoretical calculations indicate an alkaline shift of 2.8 pH units in the pK a of the ε-amino group of Lys213 upon Phe216Tyr mutation. © 2006 Springer Science+Business Media, LLC.