Import Pathway of Nuclear-Encoded Cytochrome c Oxidase Subunit 2 Using Yeast as a Model

Abstract

Subunit 2 of cytochrome c oxidase (Cox2) is a mitochondrial-encoded protein in most organisms. In soybean Glycine max a second Cox2 gene was identified in the nucleus which is functional, whereas the mitochondrial-encoded cox2 gene is silent. For import and sorting of the nuclear-encoded soybean Cox2 protein (GmCox2p) into mitochondria, the protein has acquired an N-terminal extension of 136 amino acid residues that is cleaved off in three steps during import. To study the function and processing of the GmCox2p leader peptide, we used yeast as a model system. Using different leader peptide-GFP constructs, we were able to show that the i₁ intermediate is generated in the mitochondrial matrix and the mature protein is generated in the inner membrane space. Mitochondrial processing peptidase (MPP) is involved in processing the first part of the leader peptide, processing of the last part is catalysed by the inner membrane peptidase (IMP). Oxa1p is necessary for insertion of the protein into the inner mitochondrial membrane. GmCox2p therefore utilises many of the same components as its mitochondrial-encoded predecessor, for sorting and maturation, following its import into the mitochondria.

Key words

Cox2 - mitochondrial signal peptidases - protein transport - Oxa1p - soybean.

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