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A Look at a Cholesterol Transporter

Low density lipoproteins (LDL) transport cholesterol and triglycerides to various cells and tissues throughout the body. The receptor-mediated uptake of LDL is triggered by apolipoprotein B-100, which is the only protein component of LDL. Human apolipoprotein B-100 is a glycoprotein with a molecular mass of about 550 kDa. It associates with hydrophobic molecules in a noncovalent fashion to facilitate their transport and targeting in a hydrophilic environment. Because of the protein's size and hydrophobic nature, its structure is not well characterized.

An ab initio model of apoB-100.

In this Paper of the Week, Alexander Johs and colleagues present a low resolution structure of solubilized apolipoprotein B-100. Using small angle neutron scattering in combination with advanced shape reconstruction algorithms, the researchers generated a three-dimensional model of lipid-free apolipoprotein B-100. From the model, it was clear that apolipoprotein B-100 is composed of several distinct domains connected by flexible regions. The molecule assumes a curved shape with a central cavity. The researchers used the low resolution model in combination with a secondary structure prediction to construct a hypothetical domain organization of apolipoprotein B-100 on LDL. This paper is a major contribution to the field since attempts to obtain the structure of this critical cholesterol-carrying lipoprotein stretch back 3 decades.

FOOTNOTES

See referenced article, J. Biol. Chem. 2006, 281, 19732-19739

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