1. Institute de Recherche Wiame and Laboratoire de Microbiologie, Universite Libre de Bruxelles, 1 Avenue E. Gryson, 1070 Bruxelles, Belgium, Department of Biophysics, 600 South Mathews Avenue, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, Department of Chemistry, 600 South Mathews Avenue, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, and Department of Internal Medicine, University of Iowa, EMRB 340F, Iowa City, Iowa 52242