Glycans acid into cell surface

Fig. 10.3-16 Introduction of unnatural functional groups through posttranslational modification, (a) Ketones and azides can be introduced onto cell surfaces by feeding cells with unnatural sialic acid precursors, such as mannosamine derivatives 40b and c. These are incorporated into cell-surface glycans, which can be further elaborated using additional bioconjugation reactions, (b) Specific amino acid sequences can be modified using biotin ligase. Interestingly, ketobiotin" is also recognized as a substrate for the enzyme, allowing a...

Binding of influenza viruses to the human cell surface is mediated by the hemagglutinin (HA) proteins. The attachment initiates the uptake of the virus particle into the host cell. Influenza HAs bind to carbohydrates bearing sialic acids (A-acetylneuraminic acid). The human influenza virus HA proteins preferentially bind to a2-6-linked sialic acids (Fig. 8A) that are found in the upper respiratory tract of humans. In contrast, avian HA proteins preferentially bind to a2-3-hnked sialic acid (Fig. 8B) (61-63). Glycans of this type occur in the respiratory tract and intestine of birds. This way, species specificity of the influenza strains is generated and a barrier exists for avian strains infecting humans, as the sialic acid with an a2-3 linkage is rare on the cell surface of human epithelial cells in the readily accessible upper respiratory tract (61,64). 

Vesicles containing proteins destined for intracellular use in lysosomes or outer membranes bud off from the trans face of the Golgi. Depending on their contents, some of the vesicles are diverted to nonsecretory vesicles by the presence of phosphomannose residues on their N-linked glycans or by possessing domains rich in hydrophobic amino acids. At the apical surface of salivary acini, the remaining vesicles accumulate as secretory vesicles. These vesicles become surrounded by myofibrils, which move the secretory vesicles to the cell membrane where they fuse and expel the saliva secretion into a small duct. The odor or taste of food provides a neuronal stimulus to the gland s myofibrils, and this stimulates salivary secretion. 

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