Conserved domain structure of beta-neurexins. Unusual cleaved signal sequences in receptor-like neuronal cell-surface proteins.
Neurexins, a family of neuronal cell-surface proteins, consist of the longer alpha-neurexins (I alpha, II alpha, and III alpha) and the shorter beta-neurexins (I beta and II beta) with identical C termini but distinct N termini. alpha-Neurexins have the structure of cell surface receptors, but the membrane topology and conservation of beta-neurexins is unknown. We have now characterized cDNA clones encoding bovine neurexins I beta and III beta, thereby demonstrating the presence of a beta-form for neurexin III and the evolutionary conservation of beta-neurexins in mammals. Similar to alpha-neurexins, beta-neurexins were found to be highly O-glycosylated after expression by transfection in COS cells, suggesting that alpha- and beta-neurexins utilize the same O-glycosylation cassette and have similar transmembrane orientations. To determine if beta-neurexins contain a cleaved or uncleaved signal sequence for membrane translocation, beta-neurexin-IgG fusion proteins were expressed in COS cells, and their N termini were directly sequenced. This revealed that the N terminus of all three beta-neurexins contains an unusual cleaved signal sequence. Together our data show that all known neurexin genes generate alpha and beta forms with similar transmembrane organizations and receptor-like structures. Due to the presence of a long atypical cleaved signal peptide, beta-neurexins contain only a short unique sequence before splicing into the alpha-neurexin sequence. Thus, beta-neurexins are essentially N terminally truncated alpha-neurexins.
Ushkaryov
Y A
YA
Howard Hughes Medical Institute, University of Texas Southwestern Medical School, Dallas 75235.
Hata
Y
Y
Ichtchenko
K
K
Moomaw
C
C
Afendis
S
S
Slaughter
C A
CA
Südhof
T C
TC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002417:Cattle; D002460:Cell Line; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000378:metabolism; D006031:Glycosylation; D008322:Mammals; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D021382:Protein Sorting Signals / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D018076:DNA, Complementary; D009419:Nerve Tissue Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; C086958:neurexin IIIbeta; C086959:neurexin Ibeta