ROLE OF BASIC-AMINO-ACIDS IN THE CLEAVAGE OF SYNTHETIC PEPTIDE-SUBSTRATES BY MITOCHONDRIAL PROCESSING PEPTIDASE

Our recent experiments using model peptides of rat malate dehydrogenas e (MDH) indicated that a proximal arginine and a distal basic amino ac id are important for processing by mitochondrial processing peptidase (MPP), [Niidome, T,, Kitada, S,, Shimokata, K,, Ogishima, T,, and Ito, A, (1994) J. Biol. Chem. 269, 24719-24722], To elucidate if the recog nition elements apply to other precursor proteins, we analyzed cleavag e of model peptides of human ornithine aminotransferase (OAT), Purifie d peptidase cleaved peptides that corresponded to N-terminal 1-25 and 3-25 at the correct site (Gly(17)-Val(18)) at nearly equal rates, Repl acement of Arg(16) (-2 position) with lysine or alanine reduced the pr ocessing efficiency by 95- and 380-fold, respectively. Either deletion from Met(1) to Arg(10) or replacement of the basic amino acids betwee n them decreased the processing efficiency considerably. A peptide con taining Arg(7) in addition to Lys(4) and Arg(10) was more effective th an the control peptide, However, a peptide with one and two consecutiv e basic amino acids in the distal region had a processing efficiency c lose to the control peptide, These results indicated that processing o f OAT was enhanced by an increase in the number of basic amino acids w ith a suitable distance between them. In other respects, the processin g signal of OAT was essentially the same as that of MDH.