Cysteines

Cysteine bridges are a good way to stabilize proteins. They stabilize mainly by influencing δS in δG = δH - T*δS.

Cysteine bridges are mainly found in small molecules and in molecules like snake poison. Why?

Look at crambin again:

Figure 34. You see three cysteine bridges in crambin. Shown in this orientation, I see anything striking. You too?

There are multiple ways to describe a cys-cys bridge. The most obvious way is to list the coordinates. But there are ways to do it with many fewer numbers. Can you think of a few ways?

Question 24:

1. How do cysteine bridges stabilize proteins? I.e. where do the δH, and δG come from? (Actually I should say δδH, and δδG; why)?
2. Which of the three cysteine bridges contributes most to the stability of crambin?
3. Why do we find more cysteine bridges in small proteins than in big ones?