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The Sema domain, a protein interacting module, of semaphorins and plexins Both semaphorins and plexins have a Sema domain on their N-termini. Plexins function as receptors for the semaphorins. Evolutionarily, plexins may be the ancestor of semaphorins. Semaphorins are regulatory molecules in the development of the nervous system and in axonal guidance. They also play important roles in other biological processes, such as angiogenesis, immune regulation, respiration systems, and cancer. Semaphorins can be divided into 7 classes. Vertebrates have members in classes 3-7, whereas classes 1 and 2 are known only in invertebrates. Class 2 and 3 semaphorins are secreted; classes 1 and 4 through 6 are transmembrane proteins; and class 7 is membrane associated via glycosylphosphatidylinositol (GPI) linkage. Plexins are a large family of transmembrane proteins, which are divided into four types (A-D) according to sequence similarity. In vertebrates, type A plexins serve as co-receptors for neuropilins to mediate the signalling of class 3 semaphorins. Plexins serve as direct receptors for several other members of the semaphorin family: class 6 semaphorins signal through type A plexins and class 4 semaphorins through type B plexins. This family also includes the MET and RON receptor tyrosine kinases. The Sema domain is located at the N-terminus and contains four disulfide bonds formed by eight conserved cysteine residues. It serves to recognize and bind receptors. |
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Jiyao W et al.(2023). "The conserved domain database in 2023.",