Protein Domains: Structure, Function, and Methods

In the three-dimensional structure of proteins, domains are stably folded structural units that retain molecular function independent of the rest of the larger protein. Here we review the basic building blocks of protein structure, provide an overview of molecular functions of protein domains for macromolecular interactions, ligand binding, and catalysis, summarize structural and bioinformatic approaches for identifying and classifying protein domains, and discuss the roles of protein domains as modules in the combinatorial evolution of protein structure and function.