How Soft Is a Protein? A Protein Dynamics Force Constant Measured by Neutron Scattering

An effective environmental force constant is introduced to quantify the molecular resilience (or its opposite, 'softness') of a protein structure and relate it to biological function and activity. Specific resilience-function relations were found in neutron-scattering experiments on purple membranes containing bacteriorhodopsin, the light-activated proton pump of halobacteria; the connection between resilience and stability is illustrated by a study of myoglobin in different environments. Important advantages of the neutron method are that it can characterize the dynamics of any type of biological sample--which need not be crystalline or monodisperse--and that it enables researchers to focus on the dynamics of specific parts of a complex structure with deuterium labeling.
It is now well accepted that conformational flexibility is essential for enzyme catalysis and for biological molecular activity in general. But the concept of flexibility refers to molecular motions on [...]