MadSci Network: Biochemistry
Query:

Re: Are there any cyclized proteins?

Date: Thu Oct 13 11:15:45 2005
Posted By: Gilleain Torrance, Grad student, IBLS, Glasgow University
Area of science: Biochemistry
ID: 1129178859.Bc
Message:

Cyclotides! There's a whole website dedicated to these things.

It seems there is a whole class of plant proteins with both cystine knots and C<->N connections. That they are knotted as well as cyclic seems excessive to me, but I'm not a plant designing my own proteins, so what do I know.

Incidentally, there are also topologically knotted proteins that don't have cystein knots such as the one described here.

Some structures seem to have their terminii close together on purpose (for example, those proteins that form modular domains in larger structures). However, some research says that "On average, the distance between the termini is not significantly different from what would be expected based on chance".

One last thing : thermostability (the ability of some structures to survive high - even boiling - temperatures) often involves, among other things, the terminii being so close as to be electrostatically bonded to each other (sometimes called a "salt bridge").

As for the poly-proline idea - I suppose so. I understand that proteins are meant to mostly fold on the ribosome anyway, so I don't think it would be necessary to have any particular compositional bias to get them to cyclise. That said, I don't know how the cyclotides are cyclised...


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