Related Experiment Video
Updated: Aug 13, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
An increase in side chain entropy facilitates effector binding: NMR characterization of the side chain methyl group
A P Loh1, N Pawley, L K Nicholson
1Department of Chemistry, University of Wisconsin-La Crosse, La Crosse, Wisconsin 54601, USA.
Abstract:
Cdc42Hs is a signal transduction protein that is involved in cytoskeletal growth and organization. We describe here the methyl side chain dynamics of three forms of (2)H,(13)C,(15)N-Cdc42Hs [GDP-bound (inactive), GMPPCP-bound (active), and GMPPCP/PBD46-bound (effector-bound)] from (13)C-(1)H NMR measurements of deuterium T(1) and T(1 rho) relaxation times. A wide variation in flexibility was observed throughout the protein, with methyl axis order parameters (S(2)(axis)) ranging from 0.2 to 0.4 (highly disordered) in regions near the PBD46 binding site to 0.8--1.0 (highly ordered) in some helices. The side chain dynamics of the GDP and GMPPCP forms are similar, with methyl groups on the PBD46 binding surface experiencing significantly greater mobility (lower S(2)(axis)) than those not on the binding surface. Binding of PBD46 results in a significant increase in the disorder and a corresponding increase in entropy for the majority of methyl groups. Many of the methyl groups that experience an increase in mobility are found in residues that are not part of the PBD46 binding interface. This entropy gain represents a favorable contribution to the overall entropy of effector binding and partially offsets unfavorable entropy losses such as those that occur in the backbone.
Related Concept Videos
Chair Conformation of Cyclohexane
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
Stability of Substituted Cyclohexanes
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
Stereoisomerism of Cyclic Compounds
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
Spin–Spin Coupling: One-Bond Coupling
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

