STRUCTURE-BASED DESIGN OF PEPTIDE PRESENTATION ON A VIRAL SURFACE: THE CRYSTAL STRUCTURE OF A PLANT/ANIMAL VIRUS CHIMERA AT 2.8Å RESOLUTION T. Lin¹, C. Porta², G. Lomonossoff2, J. E. Johnson^{1 1}Department of Molecular Biology, The Scripps Research Institute, 10666 N. Torrey Pines Rd., La Jolla, CA and ²Department of Virus Research, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK

A genetically engineered icosahedral plant virus, cowpea mosaic virus (CPMV), was employed as an expression and presentation system to display a 14 amino acid linear antigenic epitope found in a capsid protein of human rhinovirus 14 (HRV14). Gram quantities of the CPMV/HRV14 chimera were made in plants and purified particles were crystallized in a form isomorphous with wild-type CPMV. The 2.8 Å resolution structure of the chimera shows that the inserted loop is well ordered and that, if the loop were intact, a PHE residue of CPMV would be placed in a hydrophilic environment. The resultant strain must make the loop an attractive substrate for endogenous plant proteases, as roughly 80% of the inserted polypeptides are cleaved, allowing the PHE to be partially buried. Altering the PHE to an ARG should relieve the stress, reducing the propensity for cleavage and increasing the likelihood that the peptide will assume a structure closely similar to its structure in HRV14. Successful crystallization of other CPMV chimeras in forms isomorphous with the native virus suggests that this is a viable system for structure-based design of peptide presentation.