Disulfide-bond reshuffling in the evolution of an ape placental ribonuclease

Mol Biol Evol. 2007 Feb;24(2):505-12. doi: 10.1093/molbev/msl177. Epub 2006 Nov 20.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cysteine / genetics*
  • Disulfides / chemistry
  • Evolution, Molecular*
  • Hominidae
  • Humans
  • Molecular Sequence Data
  • Placenta / enzymology*
  • Pregnancy Proteins / chemistry
  • Pregnancy Proteins / genetics*
  • Pregnancy Proteins / metabolism
  • Recombinant Proteins / genetics
  • Ribonucleases / chemistry
  • Ribonucleases / genetics*
  • Ribonucleases / metabolism
  • Sequence Alignment


  • Disulfides
  • Pregnancy Proteins
  • Recombinant Proteins
  • Ribonucleases
  • RNASE8 protein, human
  • Cysteine