Title : C-mannosylation and O-fucosylation of the thrombospondin type 1 module
Abstract :
Thrombospondin-1 ( TSP-1 ) is a multidomain protein that has been implicated in cell adhesion, motility, and growth
Some of these functions have been localized to the three thrombospondin type 1 repeats (TSRs), modules of approximately 60 amino acids in length with conserved Cys and Trp residues
The Trp residues occur in WXXW patterns, which are the recognition motifs for protein C-mannosylation
This modification involves the attachment of an alpha-mannosyl residue to the C-2 atom of the first tryptophan
Analysis of human platelet TSP-1 revealed that Trp-368, -420, -423, and -480 are C-mannosylated
Mannosylation also occurred in recombinant, baculovirally expressed TSR modules from Sf9 and "High Five" cells, contradictory to earlier reports that such cells do not carry out this reaction
In the course of these studies it was appreciated that the TSRs in TSP-1 undergo a second form of unusual glycosylation
By using a novel mass spectrometric approach, it was found that Ser-377, Thr-432, and Thr-489 in the motif CSX (S/T)CG carry the O-linked disaccharide Glc-Fuc-O-Ser/Thr.
This is the first protein in which such a disaccharide has been identified, although protein O-fucosylation is well described in epidermal growth factor-like modules
Both C- and O-glycosylations take place on residues that have been implicated in the interaction of TSP-1 with glycosaminoglycans or other cellular receptors