Identification of a highly conserved hypothetical protein TON_0340 as a probable manganese-dependent phosphatase

Abstract

A hypothetical protein TON_0340 of a Thermococcus species is a protein conserved in a variety of organisms including human. Herein, we present four different crystal structures of TON-0340, leading to the identification of an active-site cavity harboring a metal-binding site composed of six invariant aspartate and glutamate residues that coordinate one to three metal ions. Biochemical and mutational analyses involving many phosphorous compounds show that TON-0340 is a Mn2+-dependent phosphatase. Mg2+ binds to TON-0340 less tightly and activates the phosphatase activity less efficiently than Mn2+. Whereas Ca2+ and Zn2+ are able to bind to the protein, they are unable to activate its enzymatic activity. Since the active-site cavity is small and largely composed of nearly invariant stretches of 11 or 13 amino acids, the physiological substrates of TON-0340 and its homologues are likely to be a small and the same molecule. The Mn2+-bound TON-0340 structure provides a canonical model for the ubiquitously present TON-0340 homologues and lays a strong foundation for the elucidation of their substrate and biological function. © 2016 Sohn et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.