High-resolution heteronuclear NMR of human ubiquitin in an aqueous liquid crystalline medium

A mixture of dihexanoyl phosphatidylcholine and dimyristoylphosphatidylcholine in water forms disc-shaped particles, often referred toas bicelles [Sanders and Schwonek (1992) Biochemistry, 31, 8898–8905].These adopt an ordered, liquid crystalline phase, which can be maintained atvery low concentrations of the bicelles (down to 3% w/v). At thisconcentration the spacing between individual bicelles, on average, exceeds300 Å. The bicelles are shown to have a negligible effect on therotational diffusion of ubiquitin as judged by the ¹⁵NT₁ values of the backbone amides relative to those inisotropic aqueous solution. The protein exhibits a residual degree ofalignment which is proportional to the bicelle concentration, andapproximately collinear with ubiquitin's rotational diffusion tensor. Thedegree of alignment obtained offers unique opportunities for studying theprotein's structure and dynamics.