[1] Univ Pittsburgh, Sch Med, Dept Biol Struct, Pittsburgh, PA 15260 USA
[2] Univ Pittsburgh, Sch Med, Pittsburgh Ctr HIV Prot Interact, Pittsburgh, PA 15260 USA
[3] MRC Lab Mol Biol, Francis Crick Ave, Cambridge CB2 0QH, England
[4] Univ Illinois, Dept Phys, Urbana, IL 61801 USA
[5] Univ Illinois, Beckman Inst, Urbana, IL 61801 USA
[6] Dana Farber Canc Inst, Dept Canc Immunol & Virol, Boston, MA 02215 USA
[7] Harvard Med Sch, Dept Med, Boston, MA 02115 USA
[8] Univ Oxford, Div Struct Biol, Henry Wellcome Bldg Genom Med, Oxford OX3 7BN, England
[9] Electron Bioimaging Ctr, Diamond Light Source, Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England
[10] Univ Delaware, Dept Chem & Biochem, Newark, DE 19716 USA