Figure 3.

Freely diffusing smFRET experiments reveal the Mg²⁺-dependent formation of the docked conformation in the (a) absence and (b) presence of 1000 nM HyCbl. Note the color scheme in a and b is only intended to represent the increasing [HyCbl]; colors do not necessarily correlate one-to-one with [HyCbl]. (c) The presence of saturating HyCbl (1000 nM, bronze circles) decreases the concentration of Mg²⁺ required to achieve half-maximal occupancy of the docked conformation (i.e., [Mg²⁺]_1/2) by ≈ 10-fold. The vertical dashed bar represents near-physiological salt conditions (see text for details). The error bars are smaller than the symbols used for each data point (Materials and Methods).