Diadenosine Oligophosphate Catabolic Enzymes in Yeast and Humans

University Of Texas Health Science Center San Antonio, San Antonio TX

Investigators

Abstract

9982645 Barnes, Larry Diadenosine 5',5'''-P1, Pn-oligophosphates [A(5')pn(5')A], generally designated as ApnA (n = 2-6), in one or more form are present in all organisms examined including humans. ApnAs participate in a number of biological processes and are potential signaling nucleotides with both intracellular and extracellular functions. ApnAs are degraded by specific enzymes that potentially impact a number of cellular functions. In humans a gene designated FHIT encodes a putative tumor suppressor, Fhit. Fhit is also an Ap3A hydrolase and a histidine triad (HIT) motif protein. In the fission yeast Schizosaccharomyces pombe, a gene designated aps1 encodes Aps1 that catalyzes the degradation of ApnA (n = 4-6) with Ap6A and Ap5A as preferred substrates. Aps1 also catalyzes the degradation of diphosphoinositol polyphosphates (PPInsP5 and [PP]2 InsP4 ). Aps1 is a mutT sequence motif protein, and it is unique among ApnA hydrolases with respect to its substrates and reaction products. The first major goal of this project is to determine structural elements of human Fhit Ap3A hydrolase that are necessary for tumor suppression and for enzyme activity based on its known X-ray crystallographic structure. The second major goal is to determine the three dimensional structure of S. pombe Ap6A hydrolase and to determine the amino acid residues required for binding and hydrolysis of substrates by Aps1. The significance of accomplishing the first major goal will be: increased understanding of the mechanism of tumor suppression by a gene (FHIT) that is mutated in many common tumors. The significance of accomplishing the second major goal will be increased knowledge of the structure and mechanism of an enzyme (Aps1) involved in modulating the effects of two classes of cellular signaling molecules (diadenosine oligophosphates and diphosphoinositol polyphosphates). The project will also contribute to the research education of graduate and professional students.