Use of Ar+ plasma etching to localize structural proteins in the capsid of herpes simplex virus type 1.

Partially cored herpes simplex virus type 1 (HSV-1) capsids (B capsids) were eroded in a low-energy (0.5-keV) Ar+ ion plasma under conditions in which the outermost structural proteins were expected to be degraded before more internal ones. After various periods of etching, the proteins remaining intact were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and determined quantitatively by densitometric scanning of the stained gels. The results showed that the major capsid polypeptide (VP5) and two other capsid proteins, VP19 and VP23, were degraded rapidly beginning as soon as capsids were exposed to the ion plasma. In contrast, significant lags were observed for erosion of VP21, VP22a, and VP24, suggesting that these proteins were available to accelerated ions only after other, more external structures had been damaged or eroded away. The results suggest that VP5, VP19, and VP23 are exposed on the surface of the capsid, while VP21, VP22a, and VP24 are found inside the capsid cavity. The experiments are consistent with the view that VP5 constitutes the major structural component of the hexavalent capsomers. It is proposed that VP19 and VP23 may form other surface structures such as the pentavalent capsomers, the capsid floor, or the intercapsomeric fibers.