Surface Appendages Flagella and Fimbriae

Periplasmic binding protein Periplasmic binding protein 

The chemotactic receptors to glucose, fructose, mannose and certain other sugars are insensitive to osmotic shock (Table 4.1) and have been shown to be integral parts of the cytoplasmic membrane. These membrane-associated receptors have been shown to be identical with enzymes II, the substrate-specific components of phosphotransferase transport (the PEP system). The essential event during sugar translocation using the PEP system is the phosphoenolpyruvate-dependent phosphorylation of the 

It is a reasonable assumption that transport systems arose before chemotaxis. The sharing of the binding proteins between an attractant chemo-sensor and the transport system for that ligand confers several benefits. Ability to move towards higher chemical concentrations is advantageous only if that compound can be efficiently transported and metabolised. The binding protein for a transport system would carry out the receptor requirement of an evolving chemosensor. 

The magnesium-activated membrane-bound adenosine triphosphatase is important in the chemoreception of divalent ions, e.g. Ca, Mg , Zn and Co in E. coli and S. typhimurium. The cation receptor is part of the 

BFi region of the enzyme. The discovery of a chemoreceptor function in BFi provides another example of the dual nature of the receptors involved in chemotaxis. 

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Surface Appendages Flagella and Fimbriae 143 Table 4.4 Properties of F and 1 Pili on coH ... 

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