PISEMA resonance assignment

TM) protein bacteriorhodopsin (bR) in oriented purple membranes. Our initial numerical studies indicated that the spectra from the two types of 2D experiments on uniformly N labeled bR would be too crowded to allow for assignment of all resonances.For this reason, our first experiments focused on samples with more diluted labeling patterns, specifically bR with N labeled methionines, i.e, Met-bR. Figure 13a shows the sequence and the tentative location of the secondary stmcture elements of bR highlighting the nine Met residues of which six or seven are expected to be in the helix region (Fig. 13b). The experimental PISEMA and HETCOR... 

The PISEMA spectrum from uniformly labeled fd coat protein showed two PISA wheels (Fig. lOA and D), indicating two a-helices, one transmembrane helix with a tilt angle of 30 and another with an 87° tilt away from the bilayer normal.The PISA wheel patterns then can be simulated, and each helix is rotated around its axis separately until the resonance pattern in the calculated PISA wheel spectrum qualitatively matches the resonances in the experimental spectra of selectively labeled samples (Fig. lOB). From this procedure, both the rotation of the two helices and the sequential assignment can be obtained. In the next step, the chemical shift and dipolar coupling frequen-... 

An alternative approach to structure determination is to fit structures to the resonance patterns in experimental PISEMA spectra when there is either no or only limited amounts of assignment information available. It is necessary to relate the geometry of a peptide to its spectrum in order to perform a structural fitting. A chain propagator (rotation operator) is defined... 

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