SUMMARY PARAGRAPH for OXA1
Oxa1p is a nuclearly-encoded insertase of the mitochondrial inner membrane that facilitates the insertion of both mitochondrially- and nuclearly-encoded proteins from the matrix into the inner membrane (5, 6, 3). A highly conserved member of the Oxa1/YidC/Alb3 protein family involved in the membrane insertion of proteins, Oxa1p has homologs in both prokaryotes and eukaryotes (7, 8, 2).
The matrix-exposed C-terminus of Oxa1p forms an alpha-helical domain that has the ability to bind to mitochondrial ribosomes. Ribosome binding and the physical interaction of translation complexes with the membrane-bound Oxa1p insertase facilitates the co-translational membrane insertion of mitochondrial translation products (3). Oxa1p is essential for the correct assembly of the cytochrome c oxidase, ATP synthase, and ubiquinol-cytochrome c oxidoreductase complexes of the mitochondrial respiratory chain (9, 10, 11). Specifically, Oxa1p is required to process the Cox2p subunit of the cytochrome c oxidase complex, and export its N- and C-termini to the intermembrane space (12, 7, 13). In the absence of a functional Oxa1p, Cox2p accumulates as its precursor form, pCoxII, and its translocation to the intermembrane space is prevented (14, 15). Oxa1p has a separable function in assembly of Atp9p, the mitochondrially-encoded subunit 9, into the F1F0-ATPase complex. In doing so, Oxa1p binds stably to fully-translated Atp9p and to other ATPase subunits (16). This is in contrast to the transient, cotranslational binding to mitochondrially-encoded subunits of cytochrome c oxidase exhibited by Oxa1p in its function as a membrane insertase for those subunits.
Oxa1p is essential for respiratory growth, and null mutations lead to complete respiratory deficiency and lack of cytochrome oxidase activity (1, 11). The oxa1 null mutant has an altered mitochondrial phospholipid composition, probably due to effects on transcription and membrane insertion of phosphatidylserine decarboxylase (Psd1p), which is a mitochondrial inner membrane enzyme largely responsible for the synthesis of mitochondrial phosphatidylethanolamine (17).
Last updated: 2008-04-29