1. Department of Macromolecular Structures, Centro Nacional de Biotecnología, CSIC, Darwin 3, 28049 Cantoblanco, Madrid, Spain
2. Departments of Cell Biology and Bioengineering, UPMC Hillman Cancer Center, University of Pittsburgh School of Medicine, 5117 Centre Avenue, Pittsburgh, PA 15213, USA
3. Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 450 Technology Drive, Pittsburgh, PA 15219, USA