Protein dynamics as seen by (quasi) elastic neutron scattering

Background: Elastic and quasielastic neutron scattering studies proved to be efficient probes of the atomic mean square displacement (MSD), a fundamental parameter for the characterization of the motion of individual atoms in proteins and its evolution with temperature and compositional environment. Scope of review: We present a technical overview of the different types of experimental situations and the infor- mation quasi-elastic neutron scattering approaches can make available. In particular, MSD can crucially depend on the time scale over which the averaging (building of the “mean”) takes place, being defined by the instrumen- tal resolution. Due to their high neutron scattering cross section, hydrogen atoms can be particularly sensitively observed with little interference by the other atoms in the sample. A few examples, including new data, are pre- sented for illustration. Major conclusions: The incoherent character of neutron scattering on hydrogen atoms restricts the information obtained to the self-correlations in the motion of individual atoms, simplifying at the same time the data analysis. On the other hand, the (often overlooked) exploration of the averaging time dependent character of MSD is cru- cial for unambiguous interpretation and can provide a wealth of information on micro- and nanoscale atomic motion in proteins. General significance: By properly exploiting the broad range capabilities of (quasi)elastic neutron scattering tech- niques to deliver time dependent characterization of atomic displacements, they offer a sensitive, direct and sim- ple to interpret approach to exploration of the functional activity of hydrogen atoms in proteins. Partial deuteration can add most valuable selectivity by groups of hydrogen atoms. “This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo”. 1. Introduction It is well established that the way protein molecules perform their functions has a fundamental dynamic dimension: fluctuations in the molecular configurations are prerequisites for the reactions to take place. A good example to visualize this is the binding of a Fe atom inside hemoglobin. For the Fe atom to physically access its binding locations inside the wound up protein macromolecule, the path only opens up from time to time by fluctuating deformations in the folded configura- tional shape. Since these molecular shape fluctuations are in practice most often determined by the temperature, the strong temperature ☆ ThisarticleispartofaSpecialIssueentitled“ScienceforLife”GuestEditor:Dr.Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo. ⁎ Correspondingauthorat:ESSERIC,PO.BOX176,22100Lund,Sweden. E-mail address: ferenc.mezei@esss.se (F. Mezei). http://dx.doi.org/10.1016/j.bbagen.2016.07.030 0304-4165/© 2016 Elsevier B.V. All rights reserved. © 2016 Elsevier B.V. All rights reserved.