Density Lipoprotein

HDL is a complex of lipids and proteins in approximately equal amounts that functions as a transporter of cholesterol in the blood. HDL is the smallest of the lipoprotein particles; it’s the densest because it contains the highest proportion of protein. The liver synthesizes these lipoproteins as complexes of apolipoproteins and phospholipid, which bear a resemblance to cholesterol-free flattened spherical lipoprotein particles. They pick up cholesterol; carry it internally, from cells by interaction with the ATP Binding Cassette Transporter A1. Lecithin-cholesterol acyltransferase (plasma enzyme) converts the free cholesterol into cholesteryl ester (a more hydrophobic form of cholesterol) which is then sequestered into the core of the lipoprotein particle ultimately making the newly synthesized HDL spherical. They increase in size as they pass through the bloodstream and integrate more cholesterol and phospholipid molecules from cells and other lipoproteins, for instance by the interaction with the ABCG1 transporter and the phospholipid transport protein. HDL transports their cholesterol generally to the liver or steroidogenic organs such as adrenals, ovary and testes by direct and indirect pathways. The release of HDL cholesterol to adrenals, ovaries and testes is important for the synthesis of steroid hormones. Since the triglycerides are not stable in HDL, they’re degraded by hepatic lipase in order that finally small HDL particles are left which resume the uptake of cholesterol from cells. The cholesterol supplied to the liver is excreted into the bile and consequently intestine either directly or indirectly after conversion into bile acids. High levels of HDL are associated with a decreased risk of atherosclerosis and coronary heart disease.

LRPAP1 is a member of the alpha-2-MRAP family. LRPAP1 cooperates with LRP1/alpha-2-macroglobulin receptor and glycoprotein 330. LRPAP1, located on the cell surface, creates a complex with the alpha 2 macroglobulin receptor light and heavy chains and has part in the pathogenesis of membrane glomerular nephritis.

LRPAP1 is a member of the alpha-2-MRAP family. LRPAP1 cooperates with LRP1/alpha-2-macroglobulin receptor and glycoprotein 330. LRPAP1, located on the cell surface, creates a complex with the alpha 2 macroglobulin receptor light and heavy chains and has part in the pathogenesis of membrane glomerular nephritis.

LDLRAP1 is a cytosolic protein that holds a phosphotyrosine binding (PTD) domain and performing as a cytosolic adaptor it couples LDLR to endocytic machinery. Mutations in LDLRAP1 are the reason for autosomal recessive hypercholesterolemia (ARH) which is a condition triggered by defective internalization of LDL receptors (LDLR) in the liver.

LDL is a low-density lipoprotein that transports cholesterol and triglycerides from the liver to peripheral tissues. LDL (like all lipoproteins) facilitates the movement of fats and cholesterol within the water based solution of the blood stream. Each natural LDL particle contains a single Apo B-100 molecule (apolipoprotein B-100 is a protein with 4536 amino acid residues) that circulates the fatty acids and keeps them soluble in the aqueous environment. Additionally, the LDL core is highly-hydrophobic, consisting of linoleate (a polyunsaturated fatty acid) and about 1500 esterified cholesterol molecules. This core is enclosed by a shell of phospholipids and unesterified cholesterol in addition to a single copy of B-100 large protein (514 kD). Even though the LDL particles are approximately 22 nm in diameter and have a mass of about 3 million Daltons, they have a mass and size distribution since the LDL particles contain a varying number of fatty acids. LDL receptors are synthesized and placed in the plasma membrane when a cell requires cholesterol. The LDL receptors scatter freely until they link to clathrin-coated pits. LDL particles in the blood stream attach to these extracellular LDL receptors. The clathrin-coated pits at that time form vesicles that are endocytosed into the cell. Once the clathrin coat is dropped, the vesicles transport the LDL and their receptors to early endosomes, onto late endosomes to lysosomes. At this point the cholesterol esters in the LDL are hydrolysed. The LDL receptors are recovered back to the plasma membrane. Since LDLs convey cholesterol to the arteries and can be retained there by arterial proteoglycans initializing the formation of plaques, increased levels are linked to atherosclerosis, and thus heart attack, stroke, and peripheral vascular disease. And so, cholesterol within LDL lipoproteins is habitually called "bad" cholesterol. This is a misconception since the cholesterol transported on LDL is the same as the one transported on other lipoprotein particles, it is in itself not "bad", rather it is how and where the cholesterol is being transported, and in what amounts ultimately, which causes adverse effects. HDL / LDL ratio can give an indication of risk for arteriosclerosis.

OLR1 is a type II membrane protein which belongs to the C-type lectin family and performs as a cell-surface receptor for Ox-LDL. Ox-LDL has a part in early ather-osclerosis, which includes the transformation of monocyte-derived macro-phages to foam cells in atherosclerotic lesions. In addition, OLR1 protein triggers the activation of the NF?B signal transduction pathway.

OLR1 is a type II membrane protein which belongs to the C-type lectin family and performs as a cell-surface receptor for Ox-LDL. Ox-LDL has a part in early ather-osclerosis, which includes the transformation of monocyte-derived macro-phages to foam cells in atherosclerotic lesions. In addition, OLR1 protein triggers the activation of the NF?B signal transduction pathway.

OLR1 is a type II membrane protein which belongs to the C-type lectin family and performs as a cell-surface receptor for Ox-LDL. Ox-LDL has a part in early ather-osclerosis, which includes the transformation of monocyte-derived macro-phages to foam cells in atherosclerotic lesions. In addition, OLR1 protein triggers the activation of the NF?B signal transduction pathway.