A calreticulin-like molecule from the human hookworm Necator americanus interacts with C1q and the cytoplasmic signalling domains of some integrins

Calreticulin was recently identified as a hookworm Necator americanus aller gen, implying secretion, and contact with cells of the immune system, or si gnificant worm attrition in the tissues of the host. As human calreticulin has been shown to bind to and neutralize the haemolytic activity of the com plement component C1q, and to be putatively involved in integrin-mediated i ntracellular signalling events in platelets, it was of interest to determin e whether a calreticulin from a successful nematode parasite of humans, wit h known immune modulatory and antihaemostatic properties, exhibited a capac ity to interfere with complement activation and to interact with integrin d omains associated with cell signalling in platelets and other leucocytes. W e can now report that recombinant calreticulin failed to demonstrate signif icant calcium binding capacity, which is a hallmark of calreticulins in gen eral and may indicate inappropriate folding following expression in a proka ryote. Nevertheless, recombinant calreticulin retained sufficient molecular architecture to bind to, and inhibit the haemolytic capacity of, human C1q . Furthermore, recombinant calreticulin reacted in surface plasmon resonanc e analysis (SPR) with peptides corresponding to cytoplasmic signalling doma ins of the integrins alpha IIb and alpha5(,) in a calcium independent manne r. SPR was also used to ratify the specificity of a polyclonal antibody to hookworm calreticulin, which was then used to assess the stage specificity of expression of the native molecule (in comparison with reverse transcript ase-polymerase chain reaction), to indicate its apparent secretion, and to purify native calreticulin from worm extracts by affinity chromatography. T his development will allow the functional tests described above to be repea ted for native calreticulin, to ascertain its role in the host-parasite rel ationship.