Substrate recognition and binding subunit of the essential mitochondrial processing protease (MPP), which cleaves the mitochondrial sequence off newly imported precursors proteins. Heterodimer of PMPCA (alpha) and PMPCB (beta) subunits, forming the mitochondrial processing protease (MPP) in which PMPCA is involved in substrate recognition and binding and PMPCB is the catalytic subunit. Belongs to the peptidase M16 family. Does not seem to have a protease activity as it lack the zinc-binding site.