| Abstract
| - Apolipoprotein CII (apoCII), a surface constituent of plasma lipoproteins, is the activator forlipoprotein lipase (LPL) and is therefore central for lipid transport in blood. The three-dimensional structureof 13C-, 15N-enriched human full-length apoCII in complex with sodium dodecyl sulfate (SDS) micellesis reported. In addition to the structure determination, 15N-relaxation measurements have been performedat two magnetic fields to characterize the dynamics of the backbone of apoCII in the complex. The relaxationdata also provided global structural constraints, viz. the orientation of helices in the complex. In addition,global constraints were derived from the fact that apoCII helices are attached to the surface of the SDSmicelle and that the hydrophobic moments of each helix faces the interior of the micelle. These threecategories of global constraints, together with the local classical NMR constraints, were sufficient todefine the 3D structure of the apoCII−SDS micelle complex. To our knowledge, this presents the firstexample in which the global structure of a protein−SDS micelle complex has been determined. TheC-terminal helix of apoCII is known to be responsible for the activation of LPL. This helix is distinguishedfrom the other helices by a higher degree of internal motion on the nanosecond time scale as shown bythe relaxation data. The overall structure and the internal dynamics, combined with previous mutationdata, give important clues toward a possible mechanism for the activation of LPL by apoCII.
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