Predicting the point at which transmembrane helices protrude from the bilayer: a model of the antenna complexes from photosynthetic bacteria

We describe a method for predicting the point at which a transmembranehelix leaves the bilayer and enters the more polar region ofthe aqueous exterior. This is achieved by comparing the relativedirections of the hydrophobic and internal faces of the transmembranehelices which should be opposite for the regions within thebilayer but equivalent for the regions on the outside. Thisinformation provides a strong constraint in the process of modellingmembrane proteins. We go on to use the approach to model themonomers of the bacterial light-harvesting antenna complexes.This information is then combined with some preliminary crystallographkdata and biochemical results to produce a 3-D model of a tetramer.