25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

Assessing site-specific water accessibility in folded and unfolded proteins using hyperpolarization-enhanced 2D HMQC NMR

27 Aug 2019, 12:30
Max Kade Auditorium (Henry Ford Building)

Max Kade Auditorium

Henry Ford Building

Talk Biological applications Biomolecules


Prof. Lucio Frydman (Department of Chemical and Biological Physics, Weizmann Institute of Science)


Hyperpolarized water is a valuable aid in biomolecular NMR. One can utilize it to achieve, under physiologically-like conditions, amide group polarizations that are orders-of-magnitude larger than their thermal counterparts. Suitable experimental procedures can exploit this to deliver 2D 1H-15N NMR correlations, with good resolution and enhanced sensitivity. The resulting signal enhancements depend on the exchange rates between amides and water protons, yielding information about solvent accessibility. This study applied the ensuing "HyperW" NMR method to four proteins, which exhibit a gamut of exchange behaviors. These included PhoA(350-471), an unfolded fragment of Alkaline Phosphatase from E. coli; barstar, a folded ribonuclease inhibitor from Bacillus amyloliquefaciens; R17, a system possessing folded and unfolded forms under slow interconversion; and drkN-SH3, an N-terminal protein domain where folded and unfolded forms interchange more rapidly and with temperature-dependent population ratios. For the unstructured PhoA4 fragment 2D HyperW sensitivity enhancements were very high, ≥300× over their thermal counterparts, expected due to fast amide exchanges that occur throughout this unfolded protein sequence. Though fully folded barstar also exhibited substantially-enhanced residues; these were not uniform, and reflected what appeared well folded but surface exposed residues. R17 showed the expected superposition of ≥100-fold enhancements for its unfolded form, coexisting with more modest enhancement for the folded. The behavior of drkN-SH3 domain was unexpected: HyperW substantially enhanced both folded and unfolded states -but foremost of all certain sites of the folded protein. A number of explanations– including cross-correlated relaxation processes, and the possibility of three-site exchange magnetization transfers– were considered to account for these preferential enhancements. Still, the most “reasonable” explanation for larger folded-site enhancements, appears to be that faster exchange rates characterize these sites than their unfolded counterparts. We discuss factors that could bring about such anomalous, hitherto unobserved behavior departing from accepted paradigms relating solvent exposure and protein fold.

Primary authors

Dr Or Szekely (The Weizmann Institute of Science) Dr Gregory L Olsen (Unvirsity of Vienna) Dr Rina Rosenzweig (The Weizmann Institute of Science) Prof. Lucio Frydman (Department of Chemical and Biological Physics, Weizmann Institute of Science)

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