Glycobiology Advance Access originally published online on June 26, 2009
Glycobiology 2009 19(10):1094-1102; doi:10.1093/glycob/cwp095
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Role of N-glycosylation of the SEA module of rodent Muc3 in posttranslational processing of its carboxy-terminal domain
Department of Gastroenterology, Southwest Hospital, Third Military Medical University, Chongqing 400038, People's Republic of China
1 To whom correspondence should be addressed: Tel: +23-65478216 (H), +23-68754124; Fax: +23-65410853; e-mail: rongquanw{at}hotmail.com
Received on April 10, 2009; revised on June 11, 2009; accepted on June 22, 2009
A prominent feature of the rodent Muc3 SEA module is the precursor cleavage event that segregates the O-glycosylated N-terminal fragment and transmembrane domain into the noncovalently attached heterodimer. There are seven potential N-glycosylation sites that occur in a cluster in the SEA module of Muc3. However, it is unknown if these sites are modified or what the function of these N-glycans may be in the SEA module. Our data show that the proteolytic cleavage of the rodent Muc3 SEA module was partially prevented by treatment with tunicamycin, an inhibitor of N-glycosylation. Each single mutant of the seven N-glycosylation sites (N1A, N2A, N3A, N4A, N5A, N6A, and N7A) and multiple mutants, including double (N34A) and triple (N345A) mutants, and mutants with four (N3457A), five (N34567A), six (N134567A and N234567A), seven (N1234567A) mutations, confirmed that all seven of these potential sites are N-glycosylated simultaneously. The proteolytic cleavage of the SEA module was not affected when it lacked only one, two, or three N-glycans, but was partially inhibited when lacking four, five, and six N-glycans. In all, 2%, 48%, 85%, and 73% of the products from N3457A, N34567A, N134567A, and N234567A transfectants, respectively, remained uncleaved. The proteolytic cleavage was completely prevented in the N1234567A transfectant, which eliminated all seven N-glycans in the SEA module. The interaction of the heterodimer was independent of the N-glycans within the rodent Muc3 SEA module. Thus, the N-glycosylation pattern constituted a control point for the modulation of the proteolytic cleavage of the SEA module.
Key words: mutation / N-glycan / proteolytic cleavage
2 These authors contribute equally.