ROLE OF ALPHA-SUBUNIT OF MITOCHONDRIAL PROCESSING PEPTIDASE IN SUBSTRATE RECOGNITION

Mitochondrial processing peptidase is a heterodimer consisting of alph a-mitochondrial processing peptidase (alpha-MPP) and beta-MPP. We inve stigated the role of alpha-MPP in substrate recognition using a recomb inant yeast MPP. Disruption of amino acid residues between 10 and 129 of the alpha-MPP did not essentially impair binding activity with beta -MPP and processing activity, whereas truncation of the C-terminal 41 amino acids led to a significant loss of binding and processing activi ty. Several acidic amino acids in the region conserved among the enzym es hom various species were mutated to asparagine or glutamine, and ef fects on processing of the precursors were analyzed. Glu(353) is requi red for processing of malate dehydrogenase, aspartate aminotransferase , and adrenodoxin precursors. Glu(377) and Asp(378) are needed only fo r the processing of aspartate aminotransferase and adrenodoxin precurs ors, both of which have a longer extension peptide than the others stu died. However, processing of the yeast alpha-MPP precursor, which has a short extension peptide of nine amino acids, was not affected by the se mutations. Thus, effects of substitution of acidic amino acids on t he processing differed with the precursor protein and depended on leng th of the extension peptides. alpha-MPP may function as a substrate-re cognizing subunit by interacting mainly with basic amino acids at a re gion distal to the cleavage site in precursors with a longer extension peptide.