The δ-proteobacteria Myxococcus xanthus displays social (S) and adventurous (A) motilities, which require pole-to-pole reversal of the motility regulator proteins. M utual gl iding motility protein C (MglC), a paralog of GTPase-activating protein M utual gl iding motility protein B (MglB), is a member of the polarity module involved in regulating motility. However, little is known about the structure and function of MglC. Here, we determined ∼1.85 Å resolution crystal structure of MglC using Se lenomethionine S ingle-wavelength a nomalous d iffraction. The crystal structure revealed that, despite sharing <9% sequence identity, both MglB and MglC adopt a R egulatory L ight C hain 7 family fold. However, MglC has a distinct ∼30° to 40° shift in the orientation of the functionally important α2 helix compared with other structural homologs. Using isothermal titration calorimetry and size-exclusion chromatography, we show that MglC binds MglB in 2:4 stoichiometry with submicromolar range dissociation constant. Using small-angle X-ray scattering and molecular docking studies, we show that the MglBC complex consists of a MglC homodimer sandwiched between two homodimers of MglB. A combination of size-exclusion chromatography and site-directed mutagenesis studies confirmed the MglBC interacting interface obtained by molecular docking studies. Finally, we show that the C-terminal region of MglB, crucial for binding its established partner MglA, is not required for binding MglC. These studies suggest that the MglB uses distinct interfaces to bind MglA and MglC. Based on these data, we propose a model suggesting a new role for MglC in polarity reversal in M. xanthus .
Myxococcus xanthus displays two types of motilities i.e. Social (S) and Adventurous (A). The pole-to-pole reversals of these motility regulator proteins is the key to this process. Here, we determined ~1.85 Å resolution crystal structure of MglC, which revealed that despite sharing <9% sequence identity, both MglB and MglC adopt Regulatory Light Chain 7 (RLC7) family fold. Interestingly, MglC is structurally unique compared to the other known RLC7 family proteins having ~30°-40° shift in the orientation of functionally important α2 helix. Using isothermal titration calorimetry and gel filtration chromatography, we show that MglC binds MglB in 2:4 stoichiometry with submicromolar range dissociation constant. Using combination of small angle X-ray scattering and molecular docking studies, we show that MglBC complex is formed by MglC homodimer sandwiched between two homodimers of MglB.In BriefKapoor et al. report the crystal structure of Myxococcus xanthus MglC, a Roadblock Light Chain 7 (RLC7) family protein, involved in polarity reversal. The structure reveals a distinct orientation of α2 helix compared to other RLC7 proteins. They also demonstrate that MglC binds a GTPase activating protein, MglB, with submicromolar range dissociation constant.HighlightsMglC adopts RLC7 fold and has distinct structural features.MglC interacts MglB to form a stable complex having submicromolar range dissociation constant.MglC homodimer is sandwiched between two MglB homodimers to form a 2:4 stoichiometric complex.
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