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.
Khatri
Ismat A
IA
Research Institute, Department of Structural Biology and Biochemistry, The Hospital for Sick Children, and University of Toronto, Toronto, Ontario, Canada.
Wang
Rongquan
R
Forstner
Janet F
JF
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