Mammalian cells, surface modification

Although chemical ligations on mammalian cell surfaces have been performed using unnatural functional groups delivered to carbohydrates [37], the number of studies of mammalian cell surface modifications with synthetic polymers remains limited [31]. In order to control biointerfacial aspects with environmental stimuli, thermoresponsive polymers were immobilized on mammalian cell surfaces. 

Kellam B, De Bank PA, Shakesheff KM. Chemical Modification of Mammalian Cell Surfaces. Chem. Soc. Rev. 2003 32 327-337. 

Methods used to demonstrate the existence of membrane phospholipid asymmetry, such as chemical labelling and susceptibility to hydrolysis or modification by phospholipases and other enzymes, are rmsuitable for dynamic studies because the rates of chemical and biochemical reactions are of a different order compared to the transmembrane translocahon of the phospholipids. Indirect methods have therefore been developed to measure the translocation rate which are consequent on the loss of membrane phospholipid asymmetry. Thus time scales appropriate to rates of lipid scrambling under resting conditions or when the forces preserving the asymmetric phospholipid distribution are disturbed can be monitored. Generally the methods rely on detecting the appearance of phosphatidylserine on the surface of cells. Methods of demonstrating Upid translocation in mammalian cells has been the subject of a recent review (Bevers etal., 1999). 

Although many proteins contain the modB carbohydrate, most of the attention has been on the analysis of two of them. One is a cell surface glycoprotein, called PsA (a.k.a. SP29), which has been cloned and sequenced. The carbohydrate modifications are located on a repeated motif, PTVT as shown by Edman degradation [68]. This sequence is typical of many of those in mammalian cell proteins which also contain O-Iinked oligosaccharides [69]. Several allelic variants of this protein from related strains of Dictyostelium discoideum contain 3-5 of these glycosylated repeats [70]. This protein... 

Epidermal growth factor (EGF) is a hormone polypeptide involved in the growth regulation of several mammalian cell types. The action of EGF is mediated through specific binding to a cell surface receptor, triggering rapid phosphorylation events and modifications in gene expression patterns. 

Yeast is the third expression system used to produce biopharmaceuticals. As mammalian systems, they possess the ability to cany out post-translational modifications of proteins, although the glycosylation pattern usually varies somewhat from the patterns observed on the native protein or on the protein expressed in mammalian cells. Two recombinant proteins expressed in Saccharomyces cerevisiae are now approved for general medical use hepatitis B surface antigen vaccine and the anticoagulant Hirudin . Alternative promising production systems, in particular transgenic animal and plant systems, are still in development but these systems have to prove that they are technically and economically attractive. 

Mammalian cell immobilization to electrode surfaces is vitally important for the construction of cell-based biosensors which hold out the promise for the development of practical methods for the screening of drugs for possible toxic side effects and for the monitoring of the effects of biochemical warfare agents. Surface modification of the substrate could effectively enhance the... 

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