O-glucosylation and O-fucosylation occur together in close proximity on the first epidermal growth factor repeat of AMACO (VWA2 protein)

AMACO (VWA2 protein) is an extracellular matrix protein of unknown function associated with certain basement membranes in skin, lung, and kidney. AMACO is a member of the von Willebrand factor A-like (VWA) domain containing protein superfamily and in addition to three VWA domains it also contains two epidermal growth factor-like domains. One of these contains the rare, overlapping consensus sequences for both O-glucosylation and O-fucosylation. In earlier studies of other proteins the attachment of either core glucose and fucose moieties or of the respective elongated glycans starting with these monosaccharides has been described. By a detailed mass spectrometric analysis we show that both elongated O-glucosylated (Xyl1-3Xyl1-3Glc) and elongated O-fucosylated glycan chains (NeuAc2-3Gal1-4GlcNAc1-3Fuc) can be attached to AMACO in close proximity on the same epidermal growth factor-like domain. It has been reported that the lack of O-fucosylation can markedly decrease secretion of proteins. However, the secretion of AMACO is not significantly affected when the glycosylation sites are mutated. The number of extracellular matrix proteins carrying the overlapping consensus sequence is very limited and it could be that these modifications have a new, yet unknown function.