Calsyntenins (Csts, CLSTN) also known as alcadeins are type I transmembrane proteins that belong to the cadherin superfamily. Their name comes from their ability to bind calcium. In birds and mammals, they consist of three family members (Cst1, 2 and 3), in nematodes one ortholog (CASY-1, originally CDH11) is known.
Cst1 (CLSTN1) was first shown to be predominantly expressed in postsynaptic membranes of excitatory neurons, Cst2 and 3 were found in an increased manner in inhibitory GABAergic neurons. Calsyntenins interact with numerous proteins such as with kinesin-1 and the APP-linker protein X11L/Mint2, and were shown to have multi-purpose functions both within and outside the nervous system.
Shortly after the calsyntenins were discovered, they were found to regulate postsynaptic calcium concentration. Later it was found that another key-function is to link vesicles to kinesin light chain (KLC) and thus to co-determine transport of distinct cargo.