1. Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom, Division of Medical Biochemistry and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory 7925, South Africa, and CEA, iBiTecS, Service d'Ingénierie Moléculaire des Protéines (SIMOPRO), Gif sur Yvette, F-91191, France