Figure 1.

Domain organization of α-neurexins and β-neurexins. Neurexins are type I transmembrane proteins with a single path transmembrane helix (TM) that separates amino-terminal extracellular from cytosolic intracellular domains. The hallmark of neurexins is a cassette of LNS(green)-EGF(orange)-LNS(green) that is repeated three times in α-neurexin (Nrxn1α), albeit with low sequence conservation (16% identity and 27% homology). β-Neurexin (Nrxn1β) starts with its own exon that encodes a signal peptide (SP) and unique 37 histidine-rich residues (blue). The remainder is identical to the corresponding α-neurexin starting from the last LNS domain. Red symbols indicate positions of up to five canonically conserved splice sites (SS#1 to SS#5), and hexamers point to N-glycosylation sites and O-glycosylation sites. EGF, epidermal growth factor-like domain; LNS, laminin-neurexin-sex hormone binding globulin.