1. Is there any disulphide bond in a quaternary structured protein?
    If yes, please provide examples.
  2. In tertiary structured proteins, what is(are) the most important characteristic(s) of tertiary structured proteins?
    a) globular in shape b) have both alpha helix and beta sheet or, is there any characteristic that I do not mention?
  • $\begingroup$ Aha, this is not a homework question, just that I feel like I do not understand protein quite thoroughly. Anyone can help? $\endgroup$ – user8007 Jun 12 '14 at 13:33

Interesting protein structure trivia question!

Disulfide bonds form more or less spontaneously when two sulfhydryl groups from cysteines are close enough to each other in the proper orientation in a reducing environment. So given this, its possible for them to exist, even though in most cases the distance between the cysteines in a disufide bridge is small and intra-domain.

Inter-domain disulfide bonds are rare. The most common example is that some immunoglobulin domains in antibodies have an intrachain disulfide bridge. I also found reference to one in a starch synthetase from rice.

In tertiary structure, the overall shape is an important one. Globular shapes are the most common, but elongated protein folds, triangular folds, rings, disk-like structures made out of wedges are popular examples of how protein structures can do amazing things when selection requires them to.

  • 2
    $\begingroup$ Surely immunoglobulin molecules are excellent examples of the involvement of disulphides in the quaternary strucure of proteins? $\endgroup$ – Alan Boyd Jun 12 '14 at 17:38
  • $\begingroup$ sorry i didnt use the same term, but i did mention this. $\endgroup$ – shigeta Jun 12 '14 at 23:02
  • $\begingroup$ Apologies Shigeta, I just didn't see it, possibly because I was still puzzled by the term 'intra-domain". I know what that means, but it doesn't map on to quaternary in my opinion. $\endgroup$ – Alan Boyd Jun 13 '14 at 5:03
  • $\begingroup$ i didn't bother to explain. I felt that a disulfide between two cysteines in different domains on the same chain would be a result of similar forces as a quaternary disulfide. I didn't really have to go there in the reply though $\endgroup$ – shigeta Jun 13 '14 at 5:15

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