Aspartyl aminopeptidase

This chapter elaborates activity, specificity and structural chemistry of aspartyl aminopeptidase. Aspartyl aminopeptidase has little or no activity toward aminoacyl-arylamides. Its inability to cleave simple substrates such as Asp-NHNap or Glu-NHNap explains why this enzyme has been largely overlooked. The enzyme efficiently hydrolyzes peptide bonds containing an amino acid in the P1 position however. To measure the enzymatic activity, a simple coupled assay was developed employing excess dipeptidylpeptidase IV. The cDNA of human DAP encodes a protein of 475 amino acids with a molecular weight of 52,428 and a theoretical pi of 7.03. The native enzyme is therefore apparently a homooctamer. DAP is a cytosolic enzyme and its sequence contains no membrane-spanning domains. Its sequence places it as part of the MH clan of co-catalytic metallopeptidases and it is a member of the Ml8 family. The sequence of DAP is highly conserved. Sequences with high homology have been found in Arabidopsis thaliana, Saccharomyces cerevisiae, Caenorhabditis elegans and Neurospora crassa among others. There is 49.4% amino acid identity between the human and the Arabidopsis sequences. There are no other related sequences in the human genome and DAP is the only known mammalian member of the Ml8 family.