Mapping the surface‐exposed regions of papaya mosaic virus nanoparticles

In general, the structure of the papaya mosaic virus (PapMV) and other members of the potexviruses is poorly understood. Production of PapMV coat proteins in a bacterial expression system and their self‐assembly in vitro into nanoparticles is a very useful tool to study the structure of this virus. Using recombinant PapMV nanoparticles that are similar in shape and appearance to the plant virus, we evaluated surface‐exposed regions by two different methods, immunoblot assay and chemical modification with 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide or diethyl‐pyrocarbonate followed by mass spectrometry. Three regions were targeted by the two techniques. The N‐ and C‐termini were shown to be surfaced exposed as expected. However, the region 125–136 was revealed for the first time as the major surface‐exposed region of the nanoparticles. The presence of linear peptides at the surface was finally confirmed using antibodies directed to those peptides. It is likely that region 125–136 plays a key role in the lifecycle of PapMV and other members of the potexvirus group. We have evaluated surface‐exposed regions of PapMV by immunoblot assay and chemical modification followed by mass spectrometry. Three regions were targeted by both techniques, the N‐ and C‐termini and region 125‐136. The N and C terminus were expected to be found at the surface, but the region 125‐136 was shown for the first time to be surface exposed on the CP of PapMV.