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Topographical studies on poliovirus capsid proteins by chemical modification and cross-linking with bifunctional reagents.

Poliovirus capsid proteins comprise 15.1 lysines in VP1, 5.6 lysines in VP2, 11.7 lysines in VP3 and 5.5 lysines in VP4. Treatment with monofunctional reagent N-succinimidyl 2,3-3H-proprionate leads to the modification of 3.4 lysines in VP1, 0.6 lysines in VP2, 2.0 lysines in VP3 and 0.03 lysines in VP4. Chemical modification with the monofunctional reagent N-succinimidyl 3-(4-hydroxy,5-125I-iodophenyl)propionate results in a predominant labelling of VP1 and VP3, whereas VP2 is less accessible and VP4 is not modified. Cross-linking of poliovirus with bifunctional imidoesters, dimethyl suberimidate (DMS, 1.1 nm) and dimethyl adipimidate (DMA, 0.8 nm) leads to a new protein complex of mol. wt. which corresponds to the sum of VP1 and VP3. By cleavage with ammonia and electrophoresis on polyacrylamide gels in SDS, the proteins are identified as VP1 and VP3. This result gives evidence for a direct neighbourhood of VP1 and VP3 in the virus capsid. Treatment of the virus with the mono- and bifunctional reagents has no influence on the stability of the particle. The infectivity is reduced only by the bifunctional reagent.