MAMMALIAN MITOCHONDRIAL INTERMEDIATE PEPTIDASE - STRUCTURE-FUNCTION ANALYSIS OF A NEW HOMOLOG FROM SCHIZOPHYLLUM-COMMUNE AND RELATIONSHIP TO THIMET OLIGOPEPTIDASES

Mitochondrial intermediate peptidase (MIP) is a component of the mitoc hondrial protein import machinery required for maturation of nuclear-e ncoded precursor proteins targeted to the mitochondrial matrix or inne r membrane. We previously characterized this enzyme in rat (RMIP) and Saccharomyces cerevisiae (YMIP) and showed that MIP activity is essent ial for mitochondrial function in yeast. We have now defined the struc ture of a new MIP homologue (SMIP) from the basidiomycete fungus Schiz ophyllum commune. SMIP includes 4 exons of 523, 486, 660, and 629 bp s eparated by 3 short introns. The predicted SMIP, YMIP, and RMIP sequen ces share 31-37% identity and 54-57% similarity over 700 amino acids. When SMIP and RMIP were expressed in a yeast mip1 Delta mutant; they w ere both able to rescue the respiratory-deficient phenotype caused by genetic inactivation of YMIP, indicating that the function of this enz yme is conserved in eukaryotes. Moreover, the MIP sequences show 20-24 % identity and 40-47% similarity to a family of oligopeptidases from b acteria, yeast, and mammals. MIP and these proteins are characterized by a highly conserved motif, F-H-E-X-G-H-(X)(2)-H-(X)(12)-G-(X)(5)-D-( X)(2)-E X-P-S-(X)(3)-E-X, centered around a zinc-binding site and appe ar to represent a new family of genes associated with proteolytic proc essing in the mitochondrial and cytosolic compartments. (C) 1995 Acade mic Press, Inc.