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Exploring sparsely populated states of macromolecules by diamagnetic and paramagnetic NMR relaxation
Author(s) -
Clore G. Marius
Publication year - 2011
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.576
Subject(s) - paramagnetism , relaxation (psychology) , diamagnetism , chemical physics , macromolecule , nuclear magnetic resonance spectroscopy , chemistry , spectroscopy , relaxometry , nuclear magnetic resonance , molecular physics , physics , condensed matter physics , magnetic field , medicine , psychology , social psychology , biochemistry , spin echo , quantum mechanics , magnetic resonance imaging , radiology
Sparsely populated states of macromolecules, characterized by short lifetimes and high free‐energies relative to the predominant ground state, often play a key role in many biological, chemical, and biophysical processes. In this review, we briefly summarize various new developments in NMR spectroscopy that permit these heretofore invisible, sparsely populated states to be detected, characterized, and in some instances visualized. Relaxation dispersion spectroscopy yields detailed kinetic information on processes involving species characterized by distinct chemical shifts with lifetimes in the ∼50 μs−10 ms range and populations as low as 0.5%. In the fast exchange regime (time scale less than ∼250−500 μs), the footprint of sparsely populated states can be observed on paramagnetic relaxation enhancement profiles measured on the resonances of the major species, thereby yielding structural information that is directly related to paramagnetic center‐nuclei distances from which it is possible, under suitable circumstances, to compute a structure or ensemble of structures for the minor species. Finally, differential transverse relaxation measurements can be used to detect lifetime broadening effects that directly reflect the unidirectional rates for the conversion of NMR‐visible into high‐molecular weight NMR‐invisible species. Examples of these various approaches are presented.