Semaphorins are members of a large family of proteins controlling a variety of processes in the central nervous system (CNS) during development such as cell migration and axonal growth cone guidance but are also expressed in other tissues. Their common feature is a conserved 500 amino acid “sema” domain. There are currently eight defined classes of semaphorins; classes 2 and 3 are secreted proteins while others are GPI-linked or transmembrane proteins.nSemaphorin 3A protein is an elongated disc shaped molecule with dimensions of 60X70X45 angstrom and a molecular weight of 65 kDA. The semaphorin fold is a variation of the β propeller topology with seven blades radially arranged around a central axis. Each blade averages 70 amino acids and contains a four stranded antiparallel sheet. The large size of this protein derives from the secondary structural elements attached to each blade.
