• Home
  • Search Results
  • The mechanism and high-free-energy transition state of lac repressor-lac operator interaction.

The mechanism and high-free-energy transition state of lac repressor-lac operator interaction.

Nucleic acids research (2017-10-17)
Rituparna Sengupta, Michael W Capp, Irina A Shkel, M Thomas Record

Significant, otherwise-unavailable information about mechanisms and transition states (TS) of protein folding and binding is obtained from solute effects on rate constants. Here we characterize TS for lac repressor(R)-lac operator(O) binding by analyzing effects of RO-stabilizing and RO-destabilizing solutes on association (ka) and dissociation (kd) rate constants. RO-destabilizing solutes (urea, KCl) reduce ka comparably (urea) or more than (KCl) they increase kd, demonstrating that they destabilize TS relative to reactants and RO, and that TS exhibits most of the Coulombic interactions between R and O. Strikingly, three solutes which stabilize RO by favoring burial/dehydration of amide oxygens and anionic phosphate oxygens all reduce kd without affecting ka significantly. The lack of stabilization of TS by these solutes indicates that O phosphates remain hydrated in TS and that TS preferentially buries aromatic carbons and amide nitrogens while leaving amide oxygens exposed. In our proposed mechanism, DNA-binding-domains (DBD) of R insert in major grooves of O pre-TS, forming most Coulombic interactions of RO and burying aromatic carbons. Nucleation of hinge helices creates TS, burying sidechain amide nitrogens. Post-TS, hinge helices assemble and the DBD-hinge helix-O-DNA module docks on core repressor, partially dehydrating phosphate oxygens and tightening all interfaces to form RO.

Product Number
Product Description

Tetraethylene glycol, 99%

Social Media

LinkedIn icon
Twitter icon
Facebook Icon
Instagram Icon


Research. Development. Production.

We are a leading supplier to the global Life Science industry with solutions and services for research, biotechnology development and production, and pharmaceutical drug therapy development and production.

© 2021 Merck KGaA, Darmstadt, Germany and/or its affiliates. All Rights Reserved.

Reproduction of any materials from the site is strictly forbidden without permission.