STRUCTURAL STUDIES OF ORBIVIRUS PARTICLES

We are using crystallographic methods to investigate the structure of AHSV and BTV. Our initial approach was to investigate the structure of the major protein component of the viral core, VP7(T13). This trimeri c protein has been studied in several crystal forms from both orbiviru ses and reveals a structure made up of conserved domains, capable of c onformational changes and possessing a cleavage site. Further crystall ographic analyses of native particles have provided a picture of the V P7(T13) and VP3(T2) layers of the BTV core. The VP7(T13) layer consist s of 260 trimers arranged rather symmetrically and possessing very sim ilar structures, thereby following the rules of quasi equivalence. The VP3(T2) layer is thin and contains 120 copies of 100 kDa protein arra nged as 60 approximate dimers. This type of icosahedral construction h as not been observed before and appears to contain a genome which is h ighly ordered. We anticipate that all of these features will be common to AHSV.