Toward Structural Dynamics: Protein Motions Viewed by Chemical Shift Modulations and Direct Detection of C′N Multiple-Quantum Relaxation

Mirko Mori,Mario Piccioli,Fatiha Kateb,Daniel Abergel,Geoffrey Bodenhausen

doi:10.1021/ja9103556

Abstract

Multiple quantum relaxation in proteins reveals unexpected relationships between correlated or anti-correlated conformational backbone dynamics in alpha-helices or beta-sheets. The contributions of conformational exchange to the relaxation rates of C'N coherences (i.e., double- and zero-quantum coherences involving backbone carbonyl (13)C' and neighboring amide (15)N nuclei) depend on the kinetics of slow exchange processes, as well as on the populations of the conformations and chemical shift differences of (13)C' and (15)N nuclei. The relaxation rates of C'N coherences, which reflect concerted fluctuations due to slow chemical shift modulations (CSMs), were determined by direct (13)C detection in diamagnetic and paramagnetic proteins. In well-folded proteins such as lanthanide-substituted calbindin (CaLnCb), copper,zinc superoxide dismutase (Cu,Zn SOD), and matrix metalloproteinase (MMP12), slow conformational exchange occurs along the entire backbone. Our observations demonstrate that relaxation rates of C'N coherences arising from slow backbone dynamics have positive signs (characteristic of correlated fluctuations) in beta-sheets and negative signs (characteristic of anti-correlated fluctuations) in alpha-helices. This extends the prospects of structure-dynamics relationships to slow time scales that are relevant for protein function and enzymatic activity.

Highlights

In recent years, there has been growing evidence that structural flexibility plays a key role for protein function
An unexpected relationship was found to exist between slow conformational backbone dynamics and secondary structure elements in proteins
Slow backbone dynamics were identified through relaxation rates RCSM/chemical shift modulations (CSMs) of C′N multiple quantum coherences

Summary

Introduction

There has been growing evidence that structural flexibility plays a key role for protein function. Many biochemical events such as enzymatic reactions, the formation or disruption of hydrogen bonds, the alteration of dihedral angles, and the reorientation of aromatic rings occur on slow micro- to millisecond time scales. Internal mobility is described in terms of rapid fluctuations about an average structure. These fluctuations are often modeled using local harmonic potentials, as in Normal Mode Analysis (NMA), Gaussian Network Models (GNM), Networks of Coupled (1) Levitt, M.; Sander, C.; Stern, P.

Results

Discussion

Conclusion