A novel chloride-dependent GTP-utilizing protein kinase in plasma membranes from human respiratory epithelium

The protein kinases that stimulate ion flux across airway epithelium are believed to utilize ATP as phosphate donor. Here we show that a chloride-sensitive protein kinase (in an apically enriched plasma membrane fraction from human nasal respiratory epithelium) uses guanosine 5'-triphosphate in preference to ATP as phosphate donor and is not inhibited by the protein kinase inhibitors staurosporine, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, and N-(2-guanodinoethyl)-5-isoquinoline sulfonamide. This kinase phosphorylates a 37-kDa membrane protein (p37), which exhibits a 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive phosphorylation peak at 40 mM Cl- (DIDS inhibition constant = 8 microM). p37 is additionally phosphorylated by an N-(2-guanodinoethyl)-5-isoquinoline sulfonamide-inhibitable protein kinase that uses ATP and shows a similar chloride sensitivity. The profile of membrane phosphoproteins generated by both kinases is also dependent on the source of Pi, the species of anion, and the concentration of anion. We propose a molecular mechanism for the transduction of Cl- concentration into a guanosine 5'-triphosphate-selective protein kinase signal and show that anion substitution alters the intensity of phosphorylation of membrane proteins in the absence of exogenously added protein kinases.