Neutron Scattering Reveals the Dynamic Basis of Protein Adaptation to Extreme Temperature

Moeava Tehei,Dominique Madern,Bruno Franzetti,Giuseppe Zaccai

doi:10.1074/jbc.m508417200

Abstract

To explore protein adaptation to extremely high temperatures, two parameters related to macromolecular dynamics, the mean square atomic fluctuation and structural resilience, expressed as a mean force constant, were measured by neutron scattering for hyperthermophilic malate dehydrogenase from Methanococcus jannaschii and a mesophilic homologue, lactate dehydrogenase from Oryctolagus cunniculus (rabbit) muscle. The root mean square fluctuations, defining flexibility, were found to be similar for both enzymes (1.5 A) at their optimal activity temperature. Resilience values, defining structural rigidity, are higher by an order of magnitude for the high temperature-adapted protein (0.15 Newtons/meter for O. cunniculus lactate dehydrogenase and 1.5 Newtons/meter for M. jannaschii malate dehydrogenase). Thermoadaptation appears to have been achieved by evolution through selection of appropriate structural rigidity in order to preserve specific protein structure while allowing the conformational flexibility required for activity.

Highlights

Hyperthermophilic organisms grow at temperatures above 80 °C
In terms of a force field, the width of the potential well in which an atom moves is a measure of its flexibility in terms of a root mean square fluctuation amplitudeϽu2Ͼ), whereas the detailed shape of the well reflects the rigidity of the structure, in terms of an effective force constant (ϽkϾ)
The potential is given by V(u) ϭ 1 ϽkϾu2, and the atomic mean square fluctuation is related to the force constant by Ͻu2(T)Ͼ ϭ kBT/ ϽkϾ [10, 11]; a less rigid harmonic structure is more flexible

Summary

Introduction

Hyperthermophilic organisms grow at temperatures above 80 °C. Proteins from these organisms are themselves optimally active between 60 and 125 °C and serve as paradigms for the characterization of factors responsible for protein fold stability and flexibility. In terms of a force field, the width of the potential well in which an atom moves is a measure of its flexibility in terms of a root mean square fluctuation amplitude͌Ͻu2Ͼ), whereas the detailed shape of the well reflects the rigidity of the structure, in terms of an effective force constant (ϽkϾ). In this picture, the stability would be given by the depth of the well [9]. Flexibility and rigidity are independent parameters that, as shown below, can be obtained separately from neutron scattering data

Methods

Results

Conclusion