Insights into substrate specificity and metal activation of mammalian tetrahedral aspartyl aminopeptidase

Feb. 22, 2012

Aminopeptidases are key enzymes involved in the regulation of signaling peptide activity. Here we present a detailed biochemical and structural analysis of an evolutionary highly conserved aspartyl aminopeptidase called DNPEP. We show that this peptidase can cleave multiple physiologically relevant substrates including angiotensins and thus may play a key role in regulating neuron function. Using a combination of X-ray crystallography, X-ray absorption spectroscopy and single particle electron microscopy analysis, we provide the first detailed structural analysis of DNPEP. We show that this enzyme possesses a binuclear Zn active site in which one of the Zn ions is readily exchangeable with other divalent cations such as Mn, which strongly stimulates the enzymatic activity of the protein. The plasticity of this metal binding site suggests a mechanism for regulation of DNPEP activity. We also demonstrate that DNPEP assembles into a functionally relevant tetrahedral complex that restricts access of peptide substrates to the active site. This structural data allows rationalization of the enzyme's preference for short peptide substrates with N-terminal acidic residues. This study provides a structural basis for understanding the physiology and bioinorganic chemistry of DNPEP and other M18 family aminopeptidases.

Figure Structure and topology of DNPEP. Crystallographic structure of the DNPEP monomer.

Results from: Chen Y, Farquhar ER, Chance MR, Palczewski K, Kiser, J. J. Biol. Chem. 2012