Multiple sequence alignment of protein families showing low sequence homology: a methodological approach using database pattern-matching discriminators for G-protein-linked receptors.

A multiple alignment has been constructed, containing 37 sequences from related families of membrane-bound receptors believed to share the same structural framework as rhodopsin. Sequence homology within families was high (occasionally greater than 90%), but homology between them was generally low (20% or less). Database pattern-scanning methods were therefore used to construct a set of discriminators to aid both the task of alignment and the identification of distantly related sequences showing similar rhodopsin-like transmembrane helices. The results indicate that these discriminators are uniquely able to identify each of the transmembrane helices without major cross-reaction with similar regions in unrelated integral membrane proteins. This ability engenders more accurate alignments of the sequences and facilitates structural analysis and model building of the receptors.