A PUTATIVE METAL-BINDING SITE IN THE BETA-SUBUNIT OF RAT MITOCHONDRIAL PROCESSING PEPTIDASE IS ESSENTIAL FOR ITS CATALYTIC ACTIVITY

Mitochondrial processing peptidase (MPP) consists of alpha- and beta-s ubunits (alpha-MPP and beta-MPP). beta-MPP has a putative metal-bindin g sequence (HXXEH). To determine whether the sequence of beta-MPP is e ssential for the enzymatic activity, we individually mutated the histi dines and glutamic acid to arginines and glutamine, respectively. The wild-type and mutated beta-MPPs were co-expressed with alpha-MPP in Es cherichia coli. All three mutants had completely lost the activity, wh ereas the lost activity was recovered on the addition of wild-type bet a-MPP. The activity of the wild-type enzyme was reduced by the mutant beta-MPPs. We conclude from these observations that the HXXEH region i s involved in the formation of the active site and that beta-MPP is th e catalytic subunit of MPP.