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?