Azarkh M, Keller K, Qi M, Godt A, Yulikov M. How accurately defined are the overtone coefficients in Gd(III)-Gd(III) RIDME?
J Magn Reson 2022;
339:107217. [PMID:
35453095 DOI:
10.1016/j.jmr.2022.107217]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 04/04/2022] [Accepted: 04/05/2022] [Indexed: 06/14/2023]
Abstract
Relaxation-induced dipolar modulation enhancement (RIDME) is a pulse EPR technique that is particularly suitable to determine distances between paramagnetic centers with a broad EPR spectrum, e.g. metal-ion-based ones. As far as high-spin systems (S > ½) are concerned, the RIDME experiment provides not only the basic dipolar frequency but also its overtones, which complicates the determination of interspin distances. Here, we present and discuss in a step-by-step fashion an r.m.s.d.-based approach for the calibration of the overtone coefficients for a series of molecular rulers doubly labeled with Gd(III)-PyMTA tags. The constructed 2D total-penalty diagrams help revealing that there is no unique set of overtone coefficients but rather a certain pool, which can be used to extract distance distributions between high-spin paramagnetic centers, as determined from the RIDME experiment. This is of particular importance for comparing RIDME overtone calibration and distance distributions obtained in different labs.
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