Cation residues, Interaction with polypeptides

Interaction of Anionic Detergents with Cationic Residues in Polypeptides... 

The ionic contributions can be estimated from model studies on the interactions of surfactants with polypeptides. Thus for the n-alkylsul-phates the enthalpies of interaction with lysyl, histidyl, and arginyl residues have been measured from their interactions with polylysine, polyhistidine, and polyarginine [33]. From the numbers of cationic residues in a particular protein it is possible to estimate A ion from the expression... 

Fig 5-2. This schematic ribbon diagram shows the structure of Torpedo californica acetylcholinesterase. The diagram is color-coded green the 537-amino acid polypeptide of the enzyme monomer pink the 14 aromatic residues that line the deep aromatic gorge leading to the active site and gold and blue a model of the natural substrate for acetylcholinesterase, the neurotransmitter acetylcholine, docked in the active site. Reprinted with permission from Sussman JL, Silman I. Acetylcholinesterase Structure and use as a model for specific cation-protein interactions. Curr Opin Struct Biol. 1992 2 724. 

Although the order of affinity of PF-4 for different glycosaminogly-cans, and dissociation of their complexes with salts, are typical of nonspecific, electrostatic interactions, PF-4 is not strictly a cationic protein.452 It is probable that heparin binds to clusters of basic amino acids (two lysine pairs) near the carboxyl terminal of a polypeptide chain that has an overall preponderance of acidic amino acid residues.457 High-molecular-weight heparin species can bind two PF-4 molecules, with formation of complexes 10 to 100 times as strong as those with antithrombin.217... 

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