Conceptual diagram and subunit structures depicting the various mutations used in the present study.

<p>GroEL R231W is a fluorescent mutant of GroEL with wild-type like functional characteristics (<i>upper left</i>). Stopped-flow analysis using this mutant revealed a total of five distinct kinetic transitions that are triggered immediately after ATP binding (denoted Phases A∼D and Phase S; <i>lower left</i>), and each phase displays characteristics relevant to the chaperonin mechanism (experimental traces are derived from previous experiments described in Yoshimi <i>et al</i> <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078135#pone.0078135-Yoshimi1" target="_blank">[20]</a>). In the present study, this mutation was introduced to the corresponding sites of three separate mutants: CP86, a circularly permuted GroEL mutant (<i>upper right</i>; Gly86 is shown in <i>orange space filled form</i>), D398A, a mutant with greatly diminished ATPase activity (<i>center right</i>; Asp398 is shown in <i>purple space filled form</i> and Helix M is colored <i>orange</i>), and SR-1, a single ring GroEL variant (<i>lower right</i>; the four residues of the SR-1 mutation, Arg452, Glu461, Ser463, and Val464, are shown in <i>gray space filed form</i>). Stopped-flow analysis was performed to evaluate the effect of each mutation on the dynamics of GroEL reported by this tryptophan probe. In each of the representative subunit structures, Arg231 is shown in <i>yellow space filled form</i>, and the three domains of the GroEL subunit are colored as follows: apical; <i>red</i>, intermediate; <i>green</i>, equatorial; <i>blue</i>. Models were visualized in UCSF Chimera <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078135#pone.0078135-Pettersen1" target="_blank">[41]</a>.</p>