Comment by jyounker

I have a 30 year old book on protein structure on my shelf. One of the primary themes is the recurrence of the same structural motifs in proteins. The fact that biologic proteins use the same patterns for different functions isn't new information.

The result also fits in with the rest of biochemistry. While there are a vast variety of interesting chemicals in living things, and they do all sorts of amazing stuff, there are really only a handful of classes of chemicals.

The variety of classes of chemicals that can exist dwarfs what gets used in biochemistry. Why would we expect structure to be different?

We're in agreement though, that it would be interesting to understand what the constraints are.