Negatively charged phospholipids, role

Similarly, supersaturation of saliva with respect to calcium phosphate salts is the driving force of calculus (i.e., mineralized dental plaque) and sialolith (i.e., salivary duct stones ) formation. In these cases, negatively charged phospholipids play a crucial role Ca + ions bind to the negative charges of such lipids, and inorganic phosphate associates with the bound calcium that forms a Ca-phosphate-phospholipid complex, which is an excellent nucleus of calcium-phosphate deposition. Salivary proteins may also play a role in this process because such complex formation occurs predominantly on lipids that are protein associated. The increase of pH facilitates these processes (13). 

Zakowski, J. J., Petri, W. A., Jr., and Wagner, R. R., 1981, Role of matrix protein in assembling the membrane of vesicular stomatitis virus Reconstitution of matrix protein with negatively charged phospholipid vesicles, Biochemistry 20 3902. 

The transport properties of the acids did not respond significantly to the presence of the sink. This may be because at pH 7.4 the acids are negatively charged, as are the phospholipid membranes and also the surfactant micelles electrostatic repulsions balanced out the attractive forces due to increased membrane lipophilicity. Lowered surface pH may also play a balancing role [457]. 

While examples such as these provide evidence that strong interactions of negatively-charged membrane lipids with membrane proteins the role in maintaining asymmetric distributions of lipids aaoss biological membranes is unclear. In any event such effects are likely to be of minor importance relative to actively mediated phospholipid translocation processes. 

Interactions of proteins with membranes are quite unspecific. Accordingly, typical PH-domain proteins, such as pleckstrin and spectrin, bind with no apparent stereospecificity and with quite low affinity to phosphotidylinositol bisphosphate (PtdInsP2) and IP3 in lipid vesicles (K > 30 (J.M and 40 (xM, respectively). Moreover, whether all PH-domain proteins associate with negatively charged membrane phospholipids is not certain. However, there is the case of PLC-81, where the PH domain is instrumental in bringing the soluble, cytosolic enzyme to its membrane-bound substrate, PtdInsP2. This function is supported by deletion mutants of PLC, lacking the PH domain, which caimot find the membrane-bound substrate. Therefore, while the role of the PH-domain motif in protein-protein interactions and interconnectivity is questionable, its role in membrane attachment of soluble, cytosolic proteins is quite persuasive. 

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