Analysis of aminopeptidase function in vivo. C. Kirkpatrick , L. Colvin , R.A. Riel. Department of Genetics, Cell Biology & Development, University of Minnesota, Minneapolis, MN.

   Aminopeptidases remove N-terminal amino acids from peptides and proteins. Although all the members of this enzyme family catalyze similar hydrolytic reactions, different subfamilies of aminopeptidases have very different three dimensional structures. Many animal species express multiple aminopeptidases with overlapping substrate specificities in a variety of tissues. This complexity has made it difficult to determine their biological functions using biochemical approaches. We are taking advantage of the tools available in model organisms to gain insight into aminopeptidase function in vivo. A Drosophila aminopeptidase was identified in a two-hybrid screen using a portion of the Armadillo protein as a bait. Armadillo is a critical component of the Wingless/Wnt signal transduction pathway and participates in cell-cell adhesion as part of the adherens junctions complex. The aminopeptidase is highly expressed in the developing posterior midgut of the embryo and in the garland cells, with lower levels in the Malpighian tubules. We have generated chromosomal deletions that specifically remove the aminopeptidase gene; we are analyzing their phenotypes to determine whether this aminopeptidase plays a role in Wingless/Wnt signaling, cell adhesion, or some other process. The aminopeptidase is a member of the Pfam peptidase M17 family, which has eight members in Drosophila and two in C. elegans. We are analyzing the expression patterns of related proteins in these two organisms to assess the potential for functional overlap. These studies and future genetic analysis will provide insight into the functions of these enzymes in vivo.