Low Density Lipoprotein (LDL)


Low density lipoprotein (LDL) is part of the lipoprotein family with characteristic globular particles consisting of a core of neutral lipid (cholesterol esters and triglycerides) surrounded by a phospholipid and protein coat. LDL's primary function is the transportation of endogenous cholesterol (carrying cholesterol to body cells). Studies have shown that higher levels of type-B LDL can be linked to cardiovascular disease, and are commonly referred to as bad cholesterol (Gotto & Grundy, 1999).

Low Density Lipoprotein Structure (Encyclopaedia Britannica 2007)
Low Density Lipoprotein Structure (Encyclopaedia Britannica 2007)

Structure

Each LDL particle consists of protein and lipid components (Goldstein & Brown, 1977). The protein component of LDL is a single apolipoprotein B-100 molecule (apo B-100), which circulates the fatty acids in the lipoprotein. Apo B-100 has a mass of about 500 kDa and contains 4536 amino acids. Apo B-100 also contains carbohydrate chains consisting of galactose, mannose, glucosamine, and sialic acid residues. Apo B-100 is the protein that attracts the attention of the LDL receptor, and when the LDL becomes oxidized, apo B-100 attaches to scavenger receptors. The lipid component consists primarily of an apolar core of neutral lipids. This core is comprised of mainly cholesterol esters and trigylcerides. Surrounding the apolar core is a lipid coat of phospholipids and unesterfied cholesterol. Polyunsaturated fatty acids are very vulnerable to lipid peroxidation, which is the main mechanism behind oxidizing LDL.

General Apolipoprotein Structure.jpg
General Apolipoprotein Structure (Rupp & Peters-Libeu, 1999)

Cholsterol Ester.jpg
Cholsterol Ester Structure

Cholsterol Structure.gif
Cholesterol Structure

Triglyceride Structure.jpg
Triglyceride Structure

Phospholipid Structure.gif
Phospholipid Structure

References

Encyclopaedia Britannica. (2007). Low-Density Lipoprotein. Retrieved October 18, 2012, from Encyclopaedia Britannica: http://www.britannica.com/EBchecked/media/92254/Cutaway-view-of-a-low-density-lipoprotein-complex-The-LDL

Goldstein, J. L., & Brown, M. S. (1977). The low-density lipoprotein pathway and its relation to atherosclerosis. Annual Review of Biochemistry(46), 897-930.

Gotto, A. M., & Grundy, S. M. (1999). Lowering LDL cholesterol: questions from recent meta-analyses and subset analyses of clinical trial data issues from the interdisciplinary council on reducing the risk for coronary heart disease, ninth council meeting. Circulation(99), E1 - E7.

Rupp, B., & Peters-Libeu, C. (1999, January 21). Apolipoprotein E. Retrieved November 4, 2012, from Wikipedia: http://en.wikipedia.org/wiki/File:PBB_Protein_APOE.jpg