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==Overview==
==Overview==
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'''Low-density lipoprotein''' ('''LDL''') belongs to the [[lipoprotein]] particle family. Its size is approx. 22 nm but since LDL particles contain a changing number of fatty acids they actually have a mass and size distribution. Each native LDL particle contains a single [[apolipoprotein]] B-100 molecule (Apo B-100, a protein with 4536 [[amino acid]] residues) that circles the fatty acids keeping them soluble in the aqueous environment.<ref>{{cite journal|journal=Journal of Lipid Research|author=Segrest, J. P. ''et al''|date=September 2001|title=Structure of apolipoprotein B-100 in low density lipoproteins|volume=42|pages=1346-1367}}</ref> There is a direct association between cardiovascular death and duration of elevated plasma LDL-cholesterol (LDL-C) levels. In most cases, elevated LDL is a contribution of both polygenic factors and environmental influences.<ref name="pmid12813012">{{cite journal| author=Rader DJ, Cohen J, Hobbs HH| title=Monogenic hypercholesterolemia: new insights in pathogenesis and treatment. | journal=J Clin Invest | year= 2003 | volume= 111 | issue= 12 | pages= 1795-803 | pmid=12813012 | doi=10.1172/JCI18925 | pmc=PMC161432 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12813012 }} </ref>
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==
Physiology
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==
Biochemistry==
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===Structure===
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{| class="wikitable" border="1" style="background:PaleGoldenrod"
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|-
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| '''Lipoprotein'''|| '''Density''' || '''Size'''|| '''% Protein'''|| '''% Cholesterol'''|| '''% Triglyceride'''|| '''Major Lipid'''|| '''Apolipoprotein'''
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|- style="background:LemonChiffon"
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| '''LDL''' || || || || || || ||
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|}
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''For more information about the biochemistry of all lipoproteins, click '''[[lipoprotein|here]]'''.''
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* Low-density lipoprotein (LDL) belongs to the [[lipoprotein]] particle family. It has a discoid shape with an average diameter of approximately 20 nm.<ref name="pmid11518754">{{cite journal| author=Segrest JP, Jones MK, De Loof H, Dashti N| title=Structure of apolipoprotein B-100 in low density lipoproteins. | journal=J Lipid Res | year= 2001 | volume= 42 | issue= 9 | pages= 1346-67 | pmid=11518754 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11518754 }} </ref> However, LDL is considered a heterogeneous molecule due to fluctuating density, size, and flotation rate.
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* The average composition of LDL is 20% [[protein]], 20% [[phospholipids]], 40% cholesteryl esters, 10% unesterified [[cholesterol]], and 5% [[triglycerides]].<ref name="pmid11082530">{{cite journal| author=Hevonoja T, Pentikäinen MO, Hyvönen MT, Kovanen PT, Ala-Korpela M| title=Structure of low density lipoprotein (LDL) particles: basis for understanding molecular changes in modified LDL. | journal=Biochim Biophys Acta | year= 2000 | volume= 1488 | issue= 3 | pages= 189-210 | pmid=11082530 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11082530 }} </ref>
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* The LDL particle can be structurally divided into 3 layers according to molecular orientational behavior:
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** Outer surface layer with tangential orientation: It forms a shell composed of phospholipid monolayer to cover the core. The phospholipid monolayer is organized in a way that hydrophilic residues with polar head groups interact with the outer aqueous solvent; while the inner hydrophobic residues face the lipid interior.
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** Interfacial layer with radial orientation
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** Apolar lipid core with random orientation: It contains cholesteryl esters and triglycerides.<ref name="pmid11082530">{{cite journal| author=Hevonoja T, Pentikäinen MO, Hyvönen MT, Kovanen PT, Ala-Korpela M| title=Structure of low density lipoprotein (LDL) particles: basis for understanding molecular changes in modified LDL. | journal=Biochim Biophys Acta | year= 2000 | volume= 1488 | issue= 3 | pages= 189-210 | pmid=11082530 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11082530 }} </ref><ref name="pmid21131533">{{cite journal| author=Prassl R| title=Human low density lipoprotein: the mystery of core lipid packing. | journal=J Lipid Res | year= 2011 | volume= 52 | issue= 2 | pages= 187-8 | pmid=21131533 | doi=10.1194/jlr.E013417 | pmc=PMC3023539 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21131533 }} </ref>
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* Each native LDL particle contains a single apolipoprotein B-100 (Apo-100) molecule. Apo B-100 is a protein with 4536 [[amino acid]] residues. It encircles the fatty acids keeping them soluble in the aqueous environment.<ref name="pmid11518754">{{cite journal| author=Segrest JP, Jones MK, De Loof H, Dashti N| title=Structure of apolipoprotein B-100 in low density lipoproteins. | journal=J Lipid Res | year= 2001 | volume= 42 | issue= 9 | pages= 1346-67 | pmid=11518754 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11518754 }} </ref>
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* ApoB-100 covers the surface layer of LDL in a heterogeneous fashion, covering one hemisphere of LDL, while keeping other surfaces uncovered with exposed lipids.<ref name="pmid11082530">{{cite journal| author=Hevonoja T, Pentikäinen MO, Hyvönen MT, Kovanen PT, Ala-Korpela M| title=Structure of low density lipoprotein (LDL) particles: basis for understanding molecular changes in modified LDL. | journal=Biochim Biophys Acta | year= 2000 | volume= 1488 | issue= 3 | pages= 189-210 | pmid=11082530 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11082530 }} </ref>
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===LDL Receptors===
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===Enzymes Associated with LDL===
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==Role
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LDL’s main role is mediating metabolism and transport of [[cholesterol]]. LDL transports [[cholesterol]] and [[triglycerides]] from the [[liver]] to peripheral tissues. LDL transports approximately 70% of circulating [[cholesterol]].<ref name="pmid12813012">{{cite journal| author=Rader DJ, Cohen J, Hobbs HH| title=Monogenic hypercholesterolemia: new insights in pathogenesis and treatment. | journal=J Clin Invest | year= 2003 | volume= 111 | issue= 12 | pages= 1795-803 | pmid=12813012 | doi=10.1172/JCI18925 | pmc=PMC161432 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12813012 }} </ref> It is formed in the circulation from VLDL by the action of [[lipoprotein lipase]] (LPL).
LDL’s main role is mediating metabolism and transport of [[cholesterol]]. LDL transports [[cholesterol]] and [[triglycerides]] from the [[liver]] to peripheral tissues. LDL transports approximately 70% of circulating [[cholesterol]].<ref name="pmid12813012">{{cite journal| author=Rader DJ, Cohen J, Hobbs HH| title=Monogenic hypercholesterolemia: new insights in pathogenesis and treatment. | journal=J Clin Invest | year= 2003 | volume= 111 | issue= 12 | pages= 1795-803 | pmid=12813012 | doi=10.1172/JCI18925 | pmc=PMC161432 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12813012 }} </ref> It is formed in the circulation from VLDL by the action of [[lipoprotein lipase]] (LPL).