MITOCHONDRIAL PREPROTEIN TRANSLOCASE

Mitochondria import most of their proteins from the cytosol. Dynamic p rotein complexes in the mitochondrial outer and inner membranes are re sponsible for the specific recognition and membrane translocation of p reproteins. The preprotein translocase of the outer mitochondrial memb rane contains several import receptors and a general import pore. The preprotein translocase of the inner membrane consists of a channel int eracting with preproteins in transit and an import motor that includes the matrix heat shock protein Hsp70. Acidic patches of import compone nts are thought to guide the import of positively charged signal seque nces (acid chain hypothesis). Energy input is derived from the inner m embrane potential and ATP. Proteins in the mitochondrial matrix are re quired for proteolytic processing and folding of imported proteins. Th e dynamic nature of the membrane translocase permits sorting of prepro teins at distinct stages of the import pathway.