Family 2.A.9 - The Cytochrome Oxidase Biogenesis Family
Family ID: 52619
Mitochondria import nuclearly-encoded proteins, made in the cell
cytoplasm, into the mitochondrial matrix where their mitochondrial
targeting sequences are removed by proteolysis. They then export
some of these proteins as well some mitochondrially-encoded proteins
to the inter membrane space, or they insert them into the inner
membrane. This latter export pathway requires the membrane potential.
At least for those proteins that contain their N-termini in the
intermembrane space, export is mediated by the Oxa1p export machinery.
These export domains do not bear a net positive charge but are
neutral or negatively charged. Insertion of a membrane protein
via the Oxa1p export machinery follows the "positive-inside"
rule for membrane protein topology.
Homologues of the yeast Oxa1 protein are found in chloroplasts
of plants and in a wide variety of bacteria. The chloroplast albino
3 (ALB3) protein appears to integrate the light harvesting chlorophyll-binding
protein into thylakoid membranes using a pathway that is distinct
from the chloroplast Sec translocation pathway. Oxa1p homologues
are found ubiquitously in all living organisms. While Gram-negative
bacteria only have one homologue, several Gram-positive bacteria
and archaea have two. Eukaryotes encode in their genomes between
1 and 6 paralogues.
Oxa1 homologues exhibit 3 (Oxa1p of S. cerevisiae),
4 (the E. coli 60 kDa inner membrane protein, YidC), or 5 (the
Pseudomonas putida 60kDa protein (spP25754)) putative TMSs. One
TMS occurs at the N-termini of the bacterial proteins while the
rest are in the C-terminal domain. Thus the P. putida protein
(560 aas) exhibits putative TMSs at positions 7-23, 343-361, 371-394,
434-458 and 516-535. The E. coli protein exhibits putative TMSs
at positions 6-26, 350-370, 420-440 and 499-515. The yeast Oxa1
protein lacks the first 150 residues of the bacterial proteins
and thus lacks the N-terminal TMS. Its putative TMSs are at positions
119-139, 200-220 and 282-302.
