A Putative Metal-Binding Site in the β Subunit of Rat Mitochondrial Processing Peptidase Is Essential for Its Catalytic Activity

Abstract

Mitochondrial processing peptidase (MPP) consists of α- and β-subunits (α-MPP and β-MPP). β-MPP has a putative metal-binding sequence (HXXEH). To determine whether the sequence of β-MPP is essential for the enzymatic activity, we individually mutated the histidines and glutamic acid to arginines and glutamine, respectively. The wild-type and mutated β-MPPs were co-expressed with α-MPP in Escherichia coli. All three mutants had completely lost the activity, whereas the lost activity was recovered on the addition of wild-type β-MPP. The activity of the wild-type enzyme was reduced by the mutant β-MPPs. We conclude from these observations that the HXXEH region is involved in the formation of the active site and that β-MPP is the catalytic subunit of MPP.