Figure 2

Model of mucins and other cell surface glycoproteins/proteoglycans. The figure schematically portrays structures of four size classes of mucins as well as consensus structures for syndecans and integrins. All extracellular portions of these molecules are roughly drawn to scale. Blue squiggles represent O-linked oligosaccharides while red squiggles represent glycosaminoglycans. Integrins, syndecans and most other all surface receptors do not extend beyond 50 nm from the cell surface; however, with the exception of MUC13, mucins extend much farther due to the extende3d structures contributed by the praline-rich heavily O-glycosylated tandem repeat domains. MUC1 and MUC4 are the largest transmembrane mucins, extending >200 nm from the cell surface. The ectodomain structures of MUC16 and MUC17 are considerably shorter than those of MUC1 and MUC4, but still much larger than other surface glycoproteins. Soluble mucins, such as MUC2, 5AC, 5B and 19 are even larger, reading 500–100 nm in length.