Evidence for a second peptide cleavage in the C-terminal domain of rodent intestinal mucin Muc3.
Rat intestinal mucin Muc3 (rMuc3), like its human homologue (MUC3) and several other membrane mucins, contains a C-terminally located SEA (sea urchin sperm protein, enterokinase and agrin) module, with an intrinsic proteolytic site sequence G downward arrow SIVV (where G downward arrow S is the glycine serine cleavage site). As shown previously [Wang, Khatri and Forstner (2002) Biochem. J. 366, 623-631], expression of the C-terminal domain of rMuc3 in COS-1 cells yields a V5 epitope-tagged N-terminal glycopeptide of 30 kDa and a Myc- and His epitope-tagged C-terminal glycopeptide of 49 kDa. The present study shows that the 49 kDa membrane-anchored fragment undergoes a further cleavage reaction which decreases its size to 30 kDa. Western blotting, pulse-chase metabolic incubations, immunoprecipitation and deglycosylation with N-glycosidase F were used to detect and identify the proteolytic products. Both the first and second cleavages are presumed to facilitate solubilization of Muc3 at the apical surface of enterocytes and/or enhance the potential for Muc3 to participate in ligand-receptor and signal transduction events for enterocyte function in vivo.
Research Institute, Department of Structural Biology and Biochemistry, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
Ismat A
IA
Khatri
Rongquan
R
Wang
Janet F
JF
Forstner
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D018938:Caco-2 Cells; D002522:Chlorocebus aethiops; D000939:Epitopes / Q000032:analysis; D006801:Humans; D007700:Kinetics; D055263:Mucin-3; D055264:Mucin-4; D009077:Mucins / Q000737:chemistry* / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction
C120408:Adgrf5 protein, rat; D000939:Epitopes; C524658:MUC4 protein, human; C524651:Muc3 protein, rat; C524660:Muc4 protein, rat; D055263:Mucin-3; D055264:Mucin-4; D009077:Mucins; D010446:Peptide Fragments; D043562:Receptors, G-Protein-Coupled