We have continued our study of biological macromolecules dissolved in a very dilute, nematic liquid crystalline (LC) phase. Study of chemical shift aniostropy (CSA) of proton, carbon and nitrogen backbone atoms in the protein ubiquitin, dissolved in a LC medium, revealed distinct correlations between CSA and protein secondary structure. A method has been developed that quantitatively predicts alignment of macromolecules of known shape for the case where the LC particles are nearly neutral. This information confirmed the monomeric form of the anti-HIV protein cyanovirin-N in solution. Methods have been developed that permit measurement of dipolar couplings in slowly tumbling macromolecules. We have shown that in favorable cases it is possible to define the three-dimensional structure of a protein backbone solely on the basis of its dipolar couplings, provided that measurements can be performed in two different LC media. This development holds potential to significantly decrease the time required for protein structure determination. Dipolar couplings were used for determination of the structure of the RecA binding protein DinI, and for obtaining a high-resolution structure of the DNA dodecamer d(CGCGAATTCGCG)2.
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