Test of Functional Sequence Space Shows Less Tolerance for Mutations than Expected

When you change a tire, you expect the holes on the wheel to line up with the lug bolts on the axle. But manufacturing defects can occur. The bolts might be slightly offset, or slightly longer or shorter than spec. A bolt or two might be missing. How many defects, and how large, will still permit you to continue down the road without being stranded?

Protein interactions are a more sophisticated instance of much the same problem. Proteins must interact with other proteins, often fitting like...