Complete sequence and in vitro expression of a tissue-specific phosphatidylinositol-linked N-CAM isoform from skeletal muscle.
Neural cell adhesion molecules (N-CAMs) are a family of cell surface sialoglycoproteins encoded by a single copy gene. A full-length cDNA clone that encodes a nontransmembrane phosphatidylinositol (PI) linked N-CAM of Mr 125 x 10(3) has been isolated from a human skeletal muscle cDNA library. The deduced protein sequence encodes a polypeptide of 761 amino acids and is highly homologous to the N-CAM isoform in brain of Mr 120 x 10(3). The size difference between the 125 x 10(3). The size difference between the 125 x 10(3) Mr skeletal muscle form and the 120 x 10(3) Mr N-CAM form from brain is accounted for by the insertion of a block of 37 amino acids called MSD1, in the extracellular domain of the muscle form. Transient expression of the human cDNA in COS cells results in cell surface N-CAM expression via a putative covalent attachment to PI-containing phospholipid. Linked in vitro transcription and translation experiments followed by immunoprecipitation with anti-N-CAM antibodies demonstrate that the full-length clone of 761 amino acid coding potential produces a core polypeptide of Mr 110 x 10(3) which is processed by microsomal membranes to yield a 122 x 10(3) Mr species. Taken together, these results demonstrate that the cloned cDNA sequence encodes a lipid-linked, PI-specific phospholipase C releasable surface isoform of N-CAM with core glycopeptide molecular weight corresponding to the authentic muscle 125 x 10(3) Mr N-CAM isoform. This is the first direct correlation of cDNA and deduced protein sequence with a known PI-linked N-CAM isoform from skeletal muscle.
Barton
C H
CH
Institute of Neurology, London, UK.
Dickson
G
G
Gower
H J
HJ
Rowett
L H
LH
Putt
W
W
Elsom
V
V
Moore
S E
SE
Goridis
C
C
Walsh
F S
FS
D000595:Amino Acid Sequence; D000954:Antigens, Surface; D001483:Base Sequence; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D005803:Genes, Immunoglobulin; D006801:Humans; D007527:Isoenzymes; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D007527:Isoenzymes; D010716:Phosphatidylinositols; D010738:Type C Phospholipases