Reorientational Motions of the D96N and T46V/D96N Mutants of Bacteriorhodopsin in the Purple Membrane

Authors

  • Greg S. Harms,

    1. Department of Chemistry, University of Kansas, Lawrence, KS, USA
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  • Carey K. Johnson

    Corresponding author
    1. Department of Chemistry, University of Kansas, Lawrence, KS, USA
      *Department of Chemistry, University of Kansas, Lawrence, KS 66045, USA. Fax: 913-864-5396; e-mail: cjohnson@eureka.chem.ukans.edu
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*Department of Chemistry, University of Kansas, Lawrence, KS 66045, USA. Fax: 913-864-5396; e-mail: cjohnson@eureka.chem.ukans.edu

Abstract

Abstract— The reorientational motions of the D96N and T46V/D96N mutants of bacteriorhodopsin in purple membrane have been investigated by time-resolved linear dichroism measurements. The reorientations in the early stages of the photocycle are identical to those observed in wild-type bacteriorhodopsin: anisotropics of photocycle intermediates in both D96N and T46V/D96N are rK= 0.38±0.01, rL= 0.35±0.01, rM= 0.35±0.01. The anisotropy of the initial state, rBR, exhibits decays to zero in D96N and to negative values in T46V/D96N on the time scale of tens of milliseconds. This anisotropy decay can be explained by a model that involves the motion of unexcited or spectator proteins adjacent to a photocycling protein. The amplitude and time constants of spectator reorientational motion are similar to those that have been observed in the wild type. Contributions from the anisotropy of the N-state were detected in measurements of the T46V/D96N mutant, in which a large N-state population accumulates. The value of rN is estimated to be 0.30±0.05 in T46V/D96N.

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