268 - Leucyl aminopeptidase (plant)

Abstract

Publisher Summary This chapter examines the activity, specificity and structural chemistry of Leucyl aminopeptidase (LAP). LAPs have been purified from barley and kidney bean seeds, and after overexpression in Escherichia coli. All plant LAPs are thermostable metallopeptidases with alkaline pH optima. Both the barley and the kidney bean seed LAPs are stimulated by Mg 2+ and Mn 2+, and like the animal LAPs, bestatin abolishes the kidney bean LAP activity. The barley and the kidney bean LAPs efficiently hydrolyze peptides with Leu+ and Met+ in the PI position. P1, P2, and P3 residues influence the rate of peptide cleavage by the kidney bean LAP. The mature LAP-A of tomato, tomato His6-LAP-A fusion proteins, potato LAP preprotein and an Arabidopsis LAP-fusion protein were overexpressed in E. coli. The Arabidopsis LAP and potato pre-LAP activities were monitored in E. coli crude extracts. Based on the hydrolysis of nine amino acyl-p-nitroanilides, the potato pre-LAP cleaves substrates with N-terminal Arg-, Met- and Leu-residues. The N-terminal domains of LAPs are variable in size and primary sequence. Like the bovine LAP, tomato LAP-A and LAP-N, and potato LAP proteins are synthesized as preproteins and processed to their mature form. There is no sequence identity between the animal and the plant LAP presequences. The presequences of tomato and potato LAPs have features of plastid-targeting peptides.