An Aberrant Form of CD59 Derived from HeLa Cells

We isolated a CD59 cDNA from a HeLa cell library which encoded a mutated form of CD59, having a single base substitution (G to T) that changed Arg55 to Met. Since this mutation occurred in the vicinity of the putative active site of CD59, we expressed the aberrant form of the protein in Chinese hamster ovary cells in order to test for effects upon function. We found that the mutation did not influence complement inhibitory activity of CD59. However, the epitopes recognised by the function-blocking CD59 monoclonal antibodies BRIC229 and YTH 53.1 were significantly affected. The G to T substitution caused loss of an Mnl I restriction site which permitted PCR-RFLP analysis. All of 52 human subjects studied, and our in-house HeLa cells, were homozygous for the normal CD59 sequence, indicating that the altered sequence was not due to normal variation in the general population. Therefore this mutation probably arose spontaneously in the HeLa cell line used to generate the commercially obtained cDNA library.