BIOSPECIFIC POLYMERS - RECOGNITION OF PHOSPHORYLATED POLYSTYRENE DERIVATIVES BY ANTI-DNA ANTIBODIES

The recognition of DNA-like phosphorylated polymers by anti-DNA antibo dies from the plasma of systemic lupus erythematosus patients was evid enced a few years ago by our research group. However, the radioimmunol ogical Farr assay used for the assessment of anti-DNA antibodies adsor ption was not sensitive enough to give accurate results, particularly in the case of weak levels of antibodies. An alternative method based on the use of radiolabelled species was set up in order to check the v alidity of previous results. Polystyrene resins with different levels in phosphate groups substitution were assessed with regard to their in teractions with anti-DNA antibodies. Results show that the anti-DNA an tibodies affinity is dependent on the composition of the polymers and reaches a maximum for a composition of 17.5-22.5 mol of phosphorus per 100 mol of monomeric units. This composition corresponds to the DNA-l ike polymer previously described. A computer-assisted method was used in order to have an insight into the structure of the active sites res ponsible for the DNA-like behaviour of this polymer. Numerical simulat ions of the phosphorylation reaction were performed using a Monte Carl o method, taking the structure predictions and the environment of the phosphorylated units into account. A number of thus generated virtual polymers correlated with the experimental results of the adsorption of anti-DNA antibodies. The chemical,structure of the active site was de termined by computations introducing selected hypotheses on the struct ure of the phosphorylated units. Moreover, since the number of active sites is directly related to the number of adsorbed anti-DNA antibodie s in the experimental results, the most probable structure of the acti ve sites is proposed and compared to a fragment of DNA. Conclusions ar e that the distances between the phosphate groups in the active sites of the DNA-like polymer and in the DNA fragment are similar. Optimal c onditions for the purification of SLE sera by highly specific liquid c hromatography using phosphorylated polystyrene resins of precise compo sitions as stationary phases can thus be envisaged, as well as a new m ethod for the detection of anti-DNA antibodies.