2w5w

Publication Abstract from PubMed

Alkaline phosphatases (APs) are commercially applied enzymes that catalyze the hydrolysis of phosphate monoesters by a reaction involving three active site metal ions. We have previously identified H135 as the key residue for controlling activity of the psychrophilic TAB5 AP (TAP). In this paper we describe three X-ray crystallographic structures on TAP variants H135E and H135D in complex with a variety of metal ions. The structural analysis is supported by thermodynamic and kinetic data. The AP catalysis essentially requires octahedral coordination in the M3 site, but stability is adjusted with the conformational freedom of the metal ion. Comparison to the mesophilic E. coli alkaline phosphatase shows differences in the charge transfer network in providing the chemically optimal metal combination for catalysis. Our results provide explanation why the TAB5 and E. coli APs respond in an opposite way to mutagenesis in their active sites. They provide a lesson on chemical fine tuning and the importance of the second coordination sphere in defining metal specificity in enzymes. Understanding the framework of alkaline phosphatase catalysis is essential in the efforts to design even more powerful tools for modern biotechnology.

Coordination sphere of the third metal site is essential to the activity and metal selectivity of alkaline phosphatases.,Koutsioulis D, Lyskowski A, Maki S, Guthrie E, Feller G, Bouriotis V, Heikinheimo P Protein Sci. 2009 Nov 13. PMID:19916164^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.