Phosphatidylinositol transfer activity

Hay, J. C. and Martin, T. F. I. Phosphatidylinositol transfer protein required for ATP-dependent priming of Ca2+-activated secretion. Nature 366 572-575,1993. 

Monks, D.E., Aghoram, K., Courtney, P.D., DeWald, D.B., and Dewey, R.E., 2001, Hyperosmotic stress induces the rapid phosphorylation of a soybean phosphatidylinositol transfer protein homolog through activation of the protein kinases SPK1 and SPK2. Plant Cell 13 1205-1219. 

Similar approaches may be used to determine the contribution of the phosphatidylinositol- and phosphatidylcholine-specific transfer proteins to the total phosphatidylinositol and phosphatidylcholine transfer activity. The lipid transfer activity of specific transfer proteins has been shown... 

Antibodies raised against transfer proteins may be used to quantitate transfer activities. The decrease in the transfer activity as measured by a standard assay in a pH 5.1 or 105,000g supernatant preincubated with transfer protein-specific antiserum would indicate the contribution of the inhibited protein to the total activity. Helmkamp et al. (1976) used this technique to determine the relative contribution of the phosphatidylcholine-specific and phosphatidylinositol-specific transfer proteins to the total phosphatidylinositol and phosphatidylcholine transfer activities in the bovine brain, heart, and liver. 

Helmkamp (1980a) studied the effect of the fatty acid composition of the acceptor lipid on the stimulation of phosphatidylinositol transfer from rat liver microsomes to phosphatidylcholine vesicles by bovine brain exchange protein. Acceptor vesicles containing egg phosphatidylcholine or dioleoyl phosphatidylcholine gave approximately the same transfer activity, whereas dielaidoyl phosphatidylcholine or dimyristoyl phosphatidylcholine vesicles produced lower transfer rates. Zborowski and Demel (1982) used the same protein and measured the rate of transfer of phosphatidylinositol from a monolayer to phosphatidylcholine vesicles. Vesicles of egg, dioleoyl, dielaidoyl, and dipalmitoyl phosphatidylcholine, even below its phase transition temperature, all gave equivalent transfer rates. However, a reduced rate was found when dimyristoyl and dilin-oleoyl phosphatidylcholine, and other phosphatidylcholines with two polyunsaturated fatty acids, were used. Table IV shows a comparison of the transfer activities measured in the two assays. The transfer rates are expressed as a percent of the transfer rate obtained with egg phosphatidylcholine acceptor vesicles. 

Lipid transfer peptides and proteins occur in eukaryotic and prokaryotic cells. In vitro they possess the ability to transfer phospholipids between lipid membranes. Plant lipid transfer peptides are unspecific in their substrate selectivity. They bind phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and glycolipids. Some of these peptides have shown antifungal activity in vitro The sequences of lipid transfer proteins and peptides contain 91-95 amino acids, are basic, and have eight cysteine residues forming four disulfide bonds. They do not contain tryptophan residues. About 40% of the sequence adopts a helical structure with helices linked via disulfide bonds. The tertiary structure comprises four a-helices. The three-dimensional structure of a lipid transfer peptide from H. vulgare in complex with palmitate has been solved by NMR. In this structure the fatty acid is caged in a hydrophobic cavity formed by the helices. 

Sharma, P.M., Egawa, K., Huang, Y., Martin, J.L., Huvar, I., Boss, G.R., and Olefsky, J.M., 1998, Inhibition of phosphatidylinositol 3-kinase activity by adenovirus-mediated gene transfer and its effect on insulin action. J. Biol. Chem. 273 18528-18537. 

Phosphatidate is formed by successive acylations of glycerol 3-phosphate by acyl Co A. Flydrolysis of its phosphoryl group followed by acylation yields a triacylglycerol. CDP-diacylglycerol, the activated intermediate in the de novo synthesis of several phospholipids, is formed from phosphatidate and CTP. The activated phosphatidyl unit is then transferred to the hydroxyl group of a polar alcohol, such as inositol, to form a phospholipid such as phosphatidylinositol. In mammals, phosphatidylethanolamine is formed by CDP-ethanolamine and diacylglycerol. Phosphatidylethanolamine is methylated by S-adenosylmethionine to form phosphatidylcholine. In mammals, this phosphoglyceride can also be synthesized by a pathway that utilizes dietary choline. CDP-choline is the activated intermediate in this route. 

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