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Sequence and structure comparison of ATP synthase F0 subunits 6 and 8 in notothenioid fish.

ABSTRACT: Mitochondrial changes such as tight coupling of the mitochondria have facilitated sustained oxygen and respiratory activity in haemoglobin-less icefish of the Channichthyidae family. We aimed to characterise features in the sequence and structure of the proteins directly involved in proton transport, which have potential physiological implications. ATP synthase subunit a (ATP6) and subunit 8 (ATP8) are proteins that function as part of the F0 component (proton pump) of the F0F1complex. Both proteins are encoded by the mitochondrial genome and involved in oxidative phosphorylation. To explore mitochondrial sequence variation for ATP6 and ATP8 we analysed sequences from C. gunnari and C. rastrospinosus and compared them with their closely related red-blooded species and eight other vertebrate species. Our comparison of the amino acid sequence of these proteins reveals important differences that could underlie aspects of the unique physiology of the icefish. In this study we find that changes in the sequence of subunit a of the icefish C. gunnari at position 35 where there is a hydrophobic alanine which is not seen in the other notothenioids we analysed. An amino acid change of this type is significant since it may have a structural impact. The biology of the haemoglobin-less icefish is necessarily unique and any insights about these animals will help to generate a better overall understanding of important physiological pathways.

SUBMITTER: Katyal G

PROVIDER: S-EPMC8494342 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:A region was cloned from the genome of the purple non-sulphur photobacterium Rhodospirillum rubrum that contains genes coding for the membrane protein subunits of the F0 sector of ATP synthase. The clone was identified by hybridization with a synthetic oligonucleotide designed on the basis of the known protein sequence of the dicyclohexylcarbodi-imide-reactive proteolipid, or subunit c. The complete nucleotide sequence of 4240 bp of this region was determined. It is separate from an operon described previously that encodes the five subunits of the extrinsic membrane sector of the enzyme, F1-ATPase. It contains a cluster of structural genes encoding homologues of all three membrane subunits a, b and c of the Escherichia coli ATP synthase. The order of the genes in Rsp. rubrum is a-c-b'-b where b and b' are homologues. A similar gene arrangement for F0 subunits has been found in two cyanobacteria, Synechococcus 6301 and Synechococcus 6716. This suggests that the ATP synthase complexes of all these photosynthetic bacteria contain nine different polypeptides rather than eight found in the E. coli enzyme; the chloroplast ATP synthase complex is probably similar to the photosynthetic bacterial enzymes in this respect. The Rsp. rubrum b subunit is modified after translation. As shown by N-terminal sequencing of the protein, the first seven amino acid residues are removed before or during assembly of the ATP synthase complex. The subunit-a gene is preceded by a gene coding for a small hydrophobic protein, as has been observed previously in the atp operons in E. coli, bacterium PS3 and cyanobacteria. A number of features suggest that the Rsp. rubrum cluster of F0 genes is an operon. On its 5' side are found sequences resembling the -10 (Pribnow) and -35 boxes of E. coli promoters, and the gene cluster is followed by a sequence potentially able to form a stable stem-loop structure, suggesting that it acts as a rho-independent transcription terminator. These features and the small intergenic non-coding sequences suggest that the genes are cotranscribed, and so the name atp2 is proposed for this second operon coding for ATP synthase subunits in Rsp. rubrum. The finding that genes for the F0 and F1 sectors of the enzyme are in separate clusters supports the view that these represent evolutionary modules.

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Sequence and structure comparison of ATP synthase F0 subunits 6 and 8 in notothenioid fish.

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