Fig. 1. Structure of the semaphorin family. The semaphorin family contains a large number of phylogenetically conserved secreted and transmembrane proteins. The members have been divided into eight classes based on structural features, one of which includes a unique set of viral molecules. All members of the semaphorin family share a common sema domain. Abbreviations: GPI, glycosylphosphatidylinositol-anchored; Ig, immunoglobulin-like domain; Sema, Sema domain; SS, signal sequence.