Estimating the number of protein folds

A number of fundamental questions in structural biology concern the diversi ty of protein architectures (or folds). Here, we address two of them, the s ize of the universe of folds, and the distribution of sequence families amo ng them, using an analysis based on a new and rigorous statistical sampling method. In particular we show that the number of known non-transmembrane p rotein folds is approximately one half of the total that exist, and that ce rtain superfolds should exist, which accommodate dozens of non-homologous s equence families. (C) 1998 Academic Press.