Topographical Studies on Poliovirus Capsid Proteins by Chemical Modification and Cross-linking with Bifunctional Reagents

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Abstract
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 the 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 labeling 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 molecular weight which corresponds to the sum of VP1 and VP3. By cleavage with NH3 and electrophoresis on polyacrylamide gels in SDS [sodium dodecyl sulfate], the proteins are identified as VP1 and VP3. This result gives evidence for a direct neighborhood of VP1 and VP3 in the virus capsid. Treatment of the virus with the mono- and bifunctional reagents had no influence on the stability of the particle. The infectivity is reduced only by the bifunctional reagent.