Disulfide-bond reshuffling in the evolution of an ape placental ribonuclease.
Disulfide bonds play important roles in the folding and stability of proteins and are evolutionarily conserved. A classic example is RNase A (also known as bovine pancreatic ribonuclease), which contains 4 conserved disulfide bonds among 8 cysteines. However, human RNase 8, a paralog of RNase A uniquely expressed in the placenta, has lost one of the conserved cysteines but gained another, when compared with RNase 8 of various monkeys and with RNase A. We here show that both the loss and gain of the cysteines in human RNase 8 occurred in the common ancestor of African great apes (humans, chimps, and gorillas) 7-13 MYA. Computational predictions suggest changes of disulfide bonding by these cysteine substitutions. Site-directed mutagenesis indicates that if the ribonucleolytic activity is essential for RNase 8's function, the gain of the cysteine must have preceded the loss. Human RNase 8 represents one of the first examples in which the presumable evolutionary change of a disulfide bond involves 1 loss and 1 gain of cysteine, instead of 2 losses or 2 gains. Our results provide the foundation for detailed analysis toward understanding the impact of disulfide-bond reshuffling on the structure, function, and evolution of proteins in general and human RNase 8 in particular.
Zhang
Jianzhi
J
Department of Ecology and Evolutionary Biology, University of Michigan, USA. jianzhi@umich.edu .
D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000235:genetics*; D004220:Disulfides / Q000737:chemistry; D019143:Evolution, Molecular; D015186:Hominidae; D006801:Humans; D008969:Molecular Sequence Data; D010920:Placenta / Q000201:enzymology*; D011257:Pregnancy Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics; D012260:Ribonucleases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
D004220:Disulfides; D011257:Pregnancy Proteins; D011994:Recombinant Proteins; D012260:Ribonucleases; C448983:RNASE8 protein, human; D003545:Cysteine