Membrane protein structural symmetry and assembly patterns.

Abstract

The evolution of membrane proteins depends on the physicochemical constraints imposed by the lipid bilayer, and by extension, their folding mechanisms. Repetition of well-folded motifs following these rules is frequently observed within protein sequences and has allowed efficient creation of larger macromolecules capable of more complex functions. Such repeated elements within individual protein chains can result in structural symmetry, as does association of subunits into higher-order assemblies. Nevertheless, much remains to be learned about interplay between folding, assembly, symmetry, and evolution. Structural data obtained by crystallography or electron cryo-microscopy provides an evolutionary snapshot with which to examine these questions in greater detail. At the time of writing, almost 8000 membrane protein structures have been collated into our structure and symmetry database, EncoMPASS. We present a systematic analysis of these data and discuss the implications for folding, function, and evolution.