Estimation of inter-residue distances in spin labeled proteins at physiological temperatures: Experimental strategies and practical limitations

C. Altenbach, K. J. Oh, R. J. Trabanino, K. Hideg, W. L. Hubbell

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Magnetic dipolar interactions between pairs of solvent-exposed nitroxide side chains separated by approximately one to four turns along an α-helix in T4 lysozyme are investigated. The interactions are analyzed both in frozen solution (rigid lattice conditions) and at room temperature as a function of solvent viscosity. At room temperature, a novel side chain with hindered internal motion is used, along with a more commonly employed nitroxide side chain. The results suggest that methods developed for rigid lattice conditions can be used to analyze dipolar interactions between nitroxides even in the presence of motion of the individual spins, provided the rotational correlation time of the interspin vector is sufficiently long. The distribution of distances observed for the various spin pairs is consistent with rotameric equilibria in the nitroxide side chain, as observed in crystal structures. The existence of such distance distributions places important constraints on the interpretation of internitroxide distances in terms of protein structure and structural changes.

Original languageEnglish
Pages (from-to)15471-15482
Number of pages12
Issue number51
Publication statusPublished - Dec 25 2001


ASJC Scopus subject areas

  • Biochemistry

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