Attempts to purify a second cellular receptor for a coxsackievirus B3 variant, CB3-RD from HeLa cells

A coxsackievirus B3 variant, CB3-RD, isolated on rhabdomyosarcoma (RD) cells is known to bind HeLa cells at two different receptor protein sites, HR1 and HR2. Since HR2 occurs in almost 50 fold excess of HR1 in HeLa cells, purification of HR2 was attempted, to obtain its partial N-terminal amino acid sequence and its further characterization. This study describes the purification of HR2 from octylthioglucoside solubilized HeLa cell membranes (HeLa-OTG) by preparative isoelectric focusing (IEF) followed by either preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) or affinity chromatography on immobilized receptor monoclonal antibody, RmcA (RmcA-agarose). IEF of HeLA-OTG showed that both HR2 and HR1 could be well separated by this technique and focused with peak maxima around pH 3.7 and 6.7, respectively. Both RmcA and CB3-RD recognized HR2 as doublet bands (60 kD major polypeptide and a minor 55 kD polypeptide) on electroblots under non-reducing conditions. Preparative SDS-PAGE of the pool of IEF fractions containing HR2 (IEF pool) and simultaneous elution of polypeptides from the bottom of the gel during electrophoresis, is shown to be a useful technique in purifying HR2 with only one contaminating polypeptide (65 kD). However, affinity chromatography of the IEF pool on RmcA-agarose yielded HR2 without any detectable contaminating polypeptide. A quantitative chemiluminescence assay was developed to estimate the amount of HR2 on HeLa cells and in solution, when dot blotted on polyvinylidene difluoride (PVDF) membranes and probed with RmcA. Assays revealed that about 1.2% of the total HR2 present on HeLa cells could be obtained by IEF followed by affinity chromatography. Efforts are continuing to obtain sufficient quantities of purified HR2 for partial N-terminal amino acid sequencing.