Mechanisms underlying the transfer of phosphorylcholine to filarial nematode glycoproteins - a possible role for choline kinase

Phosphorylcholine (PC) is a common constituent of proteins secreted by fila rial nematodes. As this substance has been shown to interfere with immune r esponses, we are interested in designing strategies for blocking its attach ment. Towards this end, we are investigating the mechanism of incorporation of PC into filarial molecules and in the present manuscript we describe ex periments relating to elucidating the source of PC for attachment. Synthesi s of phosphatidylcholine in eukaryotic organisms can occur by a mechanism i nvolving the transfer of PC from CDP-choline to diacylglycerol (the Kennedy pathway). By (i) measuring transfer of radio-isotope labelled PC from CDP- choline to parasite molecules and (ii) employing inhibitors of CDP-choline synthesis, we have investigated whether CDP-choline can act as a source of PC for transfer to ES-62, a major secreted glycoprotein of the rodent filar ial nematode Acanthocheilonema viteae. Although we can find no evidence of this, we show that attachment of PC is blocked by hemicholinium-3, an inhib itor of choline kinase, the first enzyme in the Kennedy pathway. Thus, at l east the first step in this pathway - phosphorylation of choline, would app ear to be necessary for attachment of PC to ES-62.