Prediction of charge-induced molecular alignment: residual dipolar couplings at pH 3 and alignment in surfactant liquid crystalline phases
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Recently we reported that the alignment tensor of a biological macromolecule, which was dissolved in a dilute suspension of highly negatively charged filamentous phage at close to neutral pH, can be predicted from the molecule’s 3D charge distribution and shape (Zweckstetter et al. 2004). Here it is demonstrated that this approach is also applicable to alignment of proteins in liquid crystalline phases formed by filamentous phage at low pH. Residual dipolar couplings (RDCs) predicted by our simple electrostatic model for the B1 domain of protein G in fd phage at pH 3 fit very well with the experimental values. The sign of charge–shape predicted one-bond 1H–15N dipolar couplings for the B1 domain of protein G (GB1) was inverted at pH 3 compared to neutral pH, in agreement with experimental observations. Our predictions indicate that this is a feature specific for GB1. In addition, it is shown that RDCs induced in the protein ubiquitin by the presence of a positively charged surfactant system comprising cetylpyridinium bromide/hexanol/sodium bromide can be predicted accurately by a simple electrostatic alignment model. This shows that steric and electrostatic interactions dominate weak alignment of biomolecules for a wide range of pH values both in filamentous phage and in surfactant liquid crystalline phases.
KeywordsMolecular alignment Residual dipolar coupling Liquid crystal Electrostatics NMR Cetylpyridinium bromide Surfactant CHARMM
The author thanks Laura G. Barrientos, Tobias S. Ulmer and Wolfgang Peti for making the RDCs of GB1, GB3 and ubiquitin available. This work was supported by the Max Planck Society. M.Z. is the recipient of a DFG Emmy Noether Fellowship (ZW71/1-4).
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