Structural studies of the rotavirus protein VP6 and the inhibition of viral transcription by monoclonal antibodies directed against VP6

Objectives - Rotaviruses are the leading cause of severe gastroenteritis in infants throughout the world. The capsid, formed by three concentric protein layers, encloses 11 segments of double-stranded RNA. The proteins VP7 and VP4 compose the most external layer VP6 the intermediate layer and VP2 the most infernal shell. The latter surrounds the genome, itself associated with two enzymes, VP1 and VP3. The general architecture of rotaviruses has been well studied by cryoelectron microscopy, but to date none of the viral proteins have been crystallized. The protein VP6 represents an essential structural component in capsid stability and is also required for viral transcription. Methods - In this work, VP6 protein from the bovine strain RF rotavirus has been overproduced, crystallized and its three-dimensional structure determined by X-ray crystallography. The crystallographic model, combined with image reconstructions of the virus obtained by electron microscopy, will allow us to study different protein interactions at the atomic level inside the viral capsid. Results - VP6 is essential for viral transcription, even though no enzymatic activity could be assigned to this protein. Its role could consist of maintaining a structural stability necessary for the viral polymerase to function. Moreover; certain monoclonal antibodies directed against VP6 inhibit transcription by viral particles. Comparison of the atomic structure of VP6/inhibiting Fab and VP6/non-inhibiting Fab complexes should allow the visualization of conformational changes that may be responsible for this inhibition. (C) 1999 Editions scientifiques et medicales Elsevier SAS.