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. Author manuscript; available in PMC: 2016 Sep 11.
Published in final edited form as: J Mol Biol. 2015 Mar 19;427(18):2966–2982. doi: 10.1016/j.jmb.2015.03.008

FIGURE 8. Kinetic Model of monomer versus transpososome recognition by ClpX.

FIGURE 8

A) λNcIc-tag monomer (purple sphere) binds weakly to the pore of ClpX (blue ring) and engagement is rare leading to weak apparent affinities. Engagement of the C-tag (depicted in an orange-glowing pore) leads to a transient enzyme-substrate complex (ES*). After engagement of the Ctag, ClpX processively translocates and unfolds the native protein.

B) Each N-domain dimer (turquoise) in ClpX can bind an E-tag in a wild-type MuA complex (colored as in Fig. 5, with cartooned extensions representing domain IIIβ, red boxes for E-tags and black boxes for C-tags). Binding of a C-tag to the pore of ClpX is enhanced because additional interactions between the E-tags and N-domains of ClpX raise the effective concentration of the C-tag near the pore by restricting the search volume needed for complex formation.

C) In the MuAΔc-tagssrA complex, binding of the ssrA tag to the pore of ClpX is strong. Engagement of the ssrA tag is strong and efficient and occurs similarly whether or not the E-tag is bound to the N-domains of ClpX.