Glycocalyx proteins

The plasma membrane contains a small amount of carbohydrate (2 to 10% of the mass of the membrane) on the outer surface. This carbohydrate is found attached to most of the protein molecules, forming glycoproteins, and to some of the phospholipid molecules (<10%), forming glycolipids. Consequently, the external surface of the cell has a carbohydrate coat, or glycocalyx. 

Unlike other Eukarya, animal cells lack cell walls, though they tend to be surrounded by a highly developed glycocalyx of up to 140 nm in thickness [108]. This diffuse layer of densely packed oligosaccharides has a heterogeneous composition and is connected to the membrane via lipids or integral proteins. The boundary of the cell usually extends beyond the mere lipid bilayer with its embedded proteins, and the extracellular structures provide initial sites of interaction or are themselves targets for MAPs such as antimicrobial peptides [115]. 

Figure 1. Solute transfer across an idealised eukaryote epithelium. The solute must move from the bulk solution (e.g. the external environment, or a body fluid) into an unstirred layer comprising water/mucus secretions, prior to binding to membrane-spanning carrier proteins (and the glycocalyx) which enable solute import. Solutes may then move across the cell by diffusion, or via specific cytosolic carriers, prior to export from the cell. Thus the overall process involves 1. Adsorption 2. Import 3. Solute transfer 4. Export. Some electrolytes may move between the cells (paracellular) by diffusion. The driving force for transport is often an energy-requiring pump (primary transport) located on the basolateral or serosal membrane (blood side), such as an ATPase. Outward electrochemical gradients for other solutes (X+) may drive import of the required solute (M+, metal ion) at the mucosal membrane by an antiporter (AP). Alternatively, the movement of X+ down its electrochemical gradient could enable M+ transport in the same direction across the membrane on a symporter (SP). A, diffusive anion such as chloride. Kl-6 refers to the equilibrium constants for each step in the metal transfer process, Kn indicates that there may be more than one intracellular compartment involved in storage. See the text for details...

Philipp S, Yang XM, Cui L, Davis AM, Downey JM, Cohen MV (2006) Postconditioning protects rabbit hearts through a protein kinase C-adenosine A2b receptor cascade. Cardiovasc Res 70(2) 308-314 Platts SH, Duling BR (2004) Adenosine A3 receptor activation modulates the capillary endothelial glycocalyx. Circ Res 94(l) 77-82... 

The lag phase occurs after cell inoculation. In this phase, there is no cell division or division takes place at low specific rates. It is an adaptation period in which adherent cells may resynthesize the glycocalyx elements lost during trypsinization, bind, and spread on the substratum. During spreading, the cytoskeleton reappears and new structural proteins are synthesized (Freshney, 2005). The duration of the lag phase is dependent on at least two factors the point in the growth phase from which cells were taken in the previous culture and the inoculum concentration. Cells originating from an actively growing culture have a shorter lag phase than those from a quiescent culture. Cultures initiated at low cell densities condition the culture medium more slowly and hence increase the duration of the lag phase, which is not desirable. 

The adhesion protein FimH mediates the attachment of uropathogenic E. coli strains with the host cell glycocalyx and specifically recognizes mannosylated structures. In 2002, Lin et al. first demonstrated that the glyco-AuNP can be used as a probe for staining the binding protein on the cell surface through carbohydrate-receptor interactions [67], Man-AuNPs were used to visualize the FimH adhesins on the type I pili of E. coli via transmission electron microscopy. 

In the organism, HA occurs in many diverse forms, circulating freely, decorated with a variety of HA-binding proteins (hyaladherins), tissue-associated, intercolated into the ECM by electrostatic or covalent binding to other matrix molecules. It comprises a major portion of the intimate glycocalyx that surrounds all cells. HA can be tethered to cell surfaces by any of a number of membrane-associated receptors. Recent evidence indicates that HA also exists within cells, though little is known of the form or function of such HA. 

In addition to PEG, certain polysaccharides, such as hyaluronic acid (HA) and dextran, have been used as low protein-adsorption, low cell adhesion surface coatings. Synthetic polymer surfactants consisting of poly(vinyl amine) with dextran and alkanoyl side chains, which mimicks the glycocalyx—negatively charged sugar layer outside cell membrane, are also shown to reduce protein adsorption to hydrophobic graphite surface. ... 

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