Helix-helix interactions in membrane proteins: coarse-grained simulations of glycophorin a helix dimerization.

Oligomerization of transmembrane (TM) helices is a key stage in the folding of membrane proteins. Glycophorin A (GpA) is a well-documented test system for this process. Coarse-grained molecular dynamics (CG-MD) allows us to simulate the self-assembly of TM helices into dimers, for both wild-type (WT) and mutant GpA sequences. For the WT sequences, dimers formed rapidly and remained stable in all simulations. The resultant dimers exhibited right-handed crossing and the same interhelix contacts as in NMR structures. Simulations of disruptive mutants revealed the dimers were less stable, with values of DeltaDelta G dimerization consistent with experimental data. The dimers of disruptive mutants were distorted relative to the WT and showed left-handed crossing of their helices. CG-MD can therefore be used to explore the interactions of TM helices, an important stage in the folding of membrane proteins. In particular, CG-MD has been shown to be sensitive enough to detect disruptions introduced by mutation. Future refinement of such models via atomistic simulations will enable a multiscale approach to predict the folding of membrane proteins.