Cytochrome c oxidase assembly protein is essential for the assembly of functional cytochrome oxidase protein. In eukaryotes it is an integral protein of the mitochondrial inner membrane. Cox11 is essential for the insertion of Cu(I) ions to form the CuB site. This is essential for the stability of other structures in subunit I, for example haems a and a3, and the magnesium/manganese centre. Cox11 is probably only required in sub-stoichiometric amounts relative to the structural units []. The C-terminal region of the protein is known to form a dimer. Each monomer coordinates one Cu(I) ion via three conserved cysteine residues (111, 208 and 210) in Saccharomyces cerevisiae (). Met 224 is also thought to play a role in copper transfer or stabilising the copper site [].
Cytochrome c oxidase assembly protein is essential for the assembly of functional cytochrome oxidase protein. In eukaryotes it is an integral protein of the mitochondrial inner membrane. Cox11 is essential for the insertion of Cu(I) ions to form the CuB site. Thisis essential for the stability of other structures in subunit I, for example haems a and a3, and the magnesium/manganese centre. Cox11 is probably only required in sub-stoichiometric amounts relative to the structural units []. The C-terminal region of the protein is known to form a dimer. Each monomer coordinates one Cu(I) ion via three conserved cysteine residues (111, 208 and 210) in Saccharomyces cerevisiae (). Met 224 is also thought to play a role in copper transfer or stabilising the copper site [].The copper binding motif is composed of two highly conserved cysteines and is located on one side of a β-barrel structure [].
Ribosomes are the particles that catalyse mRNA-directed protein synthesis in all organisms. The codons of the mRNA are exposed on the ribosome to allow tRNA binding. This leads to the incorporation of amino acids into the growing polypeptide chain in accordance with the genetic information. Incoming amino acid monomers enter the ribosomal A site in the form of aminoacyl-tRNAs complexed with elongation factor Tu (EF-Tu) and GTP. The growing polypeptide chain, situated in the P site as peptidyl-tRNA, is then transferred to aminoacyl-tRNA and the new peptidyl-tRNA, extended by one residue, is translocated to the P site with the aid the elongation factor G (EF-G) and GTP as the deacylated tRNA is released from the ribosome through one or more exit sites [, ]. About 2/3 of the mass of the ribosome consists of RNA and 1/3 of protein. The proteins are named in accordance with the subunit of the ribosome which they belong to - the small (S1 to S31) and the large (L1 to L44). Usually they decorate the rRNA cores of the subunits. Many ribosomal proteins, particularly those of the large subunit, are composed of a globular, surfaced-exposed domain with long finger-like projections that extend into the rRNA core to stabilise its structure. Most of the proteins interact with multiple RNA elements, often from different domains. In the large subunit, about 1/3 of the 23S rRNA nucleotides are at least in van der Waal's contact with protein, and L22 interacts with all six domains of the 23S rRNA. Proteins S4 and S7, which initiate assembly of the 16S rRNA, are located at junctions of five and four RNA helices, respectively. In this way proteins serve to organise and stabilise the rRNA tertiary structure. While the crucial activities of decoding and peptide transfer are RNA based, proteins play an active role in functions that may have evolved to streamline the process of protein synthesis. In addition to their function in the ribosome, many ribosomal proteins have some function 'outside' the ribosome [, ].Rsm22 has been identified as a mitochondrial small ribosomal subunit []and is a methyltransferase. In Schizosaccharomyces pombe (Fission yeast), Rsm22 is tandemly fused to Cox11 (a factor required for copper insertion into cytochrome oxidase) and the two proteins are proteolytically cleaved after import into the mitochondria []. This entry consists of mitochondrial Rsm22 and homologous sequences from bacteria.
