Cholesterol is the principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils.
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested materials. Endocytosis includes pinocytosis and phagocytosis. It is a form of active transport.
HMG-CoA reductase is the rate-controlling enzyme of the mevalonate pathway, the metabolic pathway that produces cholesterol and other isoprenoids. HMGCR catalyzes the conversion of HMG-CoA to mevalonic acid, a necessary step in the biosynthesis of cholesterol. Normally in mammalian cells this enzyme is competitively suppressed so that its effect is controlled. This enzyme is the target of the widely available cholesterol-lowering drugs known collectively as the statins, which help treat dyslipidemia.
Joseph Leonard Goldstein ForMemRS is an American biochemist. He received the Nobel Prize in Physiology or Medicine in 1985, along with fellow University of Texas Southwestern researcher, Michael Brown, for their studies regarding cholesterol. They discovered that human cells have low-density lipoprotein (LDL) receptors that remove cholesterol from the blood and that when LDL receptors are not present in sufficient numbers, individuals develop hypercholesterolemia and become at risk for cholesterol related diseases, notably coronary heart disease. Their studies led to the development of statin drugs.
The low-density lipoprotein receptor (LDL-R) is a mosaic protein of 839 amino acids that mediates the endocytosis of cholesterol-rich low-density lipoprotein (LDL). It is a cell-surface receptor that recognizes apolipoprotein B100 (ApoB100), which is embedded in the outer phospholipid layer of very low-density lipoprotein (VLDL), their remnants—i.e. intermediate-density lipoprotein (IDL), and LDL particles. The receptor also recognizes apolipoprotein E (ApoE) which is found in chylomicron remnants and IDL. In humans, the LDL receptor protein is encoded by the LDLR gene on chromosome 19. It belongs to the low density lipoprotein receptor gene family. It is most significantly expressed in bronchial epithelial cells and adrenal gland and cortex tissue.
Mark Steven Bretscher is a British biological scientist and Fellow of the Royal Society. He worked at the Medical Research Council Laboratory of Molecular Biology in Cambridge, United Kingdom and is currently retired.
Sterol regulatory element-binding proteins (SREBPs) are transcription factors that bind to the sterol regulatory element DNA sequence TCACNCCAC. Mammalian SREBPs are encoded by the genes SREBF1 and SREBF2. SREBPs belong to the basic-helix-loop-helix leucine zipper class of transcription factors. Unactivated SREBPs are attached to the nuclear envelope and endoplasmic reticulum membranes. In cells with low levels of sterols, SREBPs are cleaved to a water-soluble N-terminal domain that is translocated to the nucleus. These activated SREBPs then bind to specific sterol regulatory element DNA sequences, thus upregulating the synthesis of enzymes involved in sterol biosynthesis. Sterols in turn inhibit the cleavage of SREBPs and therefore synthesis of additional sterols is reduced through a negative feed back loop.
Familial hypercholesterolemia (FH) is a genetic disorder characterized by high cholesterol levels, specifically very high levels of low-density lipoprotein cholesterol, in the blood and early cardiovascular diseases. The most common mutations diminish the number of functional LDL receptors in the liver or produce abnormal LDL receptors that never go to the cell surface to function properly. Since the underlying body biochemistry is slightly different in individuals with FH, their high cholesterol levels are less responsive to the kinds of cholesterol control methods which are usually more effective in people without FH. Nevertheless, treatment is usually effective.
Squalene synthase (SQS) or farnesyl-diphosphate:farnesyl-diphosphate farnesyl transferase is an enzyme localized to the membrane of the endoplasmic reticulum. SQS participates in the isoprenoid biosynthetic pathway, catalyzing a two-step reaction in which two identical molecules of farnesyl pyrophosphate (FPP) are converted into squalene, with the consumption of NADPH. Catalysis by SQS is the first committed step in sterol synthesis, since the squalene produced is converted exclusively into various sterols, such as cholesterol, via a complex, multi-step pathway. SQS belongs to squalene/phytoene synthase family of proteins.
Sterol regulatory element-binding protein cleavage-activating protein, also known as SREBP cleavage-activating protein or SCAP, is a protein that in humans is encoded by the SCAP gene.
The epididymal secretory protein E1, also known as NPC2, is one of two main lysosomal transport proteins that assist in the regulation of cellular cholesterol by exportation of LDL-derived cholesterol from lysosomes. Lysosomes have digestive enzymes that allow it to break down LDL particles to LDL-derived cholesterol once the LDL particle is engulfed into the cell via receptor mediated endocytosis.
Xiaodong Wang is a Chinese-American biochemist best known for his work with apoptosis, one of the ways through which cells kill themselves.
Sterol regulatory element-binding transcription factor 1 (SREBF1) also known as sterol regulatory element-binding protein 1 (SREBP-1) is a protein that in humans is encoded by the SREBF1 gene.
Sterol regulatory element-binding protein 2 (SREBP-2) also known as sterol regulatory element binding transcription factor 2 (SREBF2) is a protein that in humans is encoded by the SREBF2 gene.
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an enzyme encoded by the PCSK9 gene in humans on chromosome 1. It is the 9th member of the proprotein convertase family of proteins that activate other proteins. Similar genes (orthologs) are found across many species. As with many proteins, PCSK9 is inactive when first synthesized, because a section of peptide chains blocks their activity; proprotein convertases remove that section to activate the enzyme. The PCSK9 gene also contains one of 27 loci associated with increased risk of coronary artery disease.
Membrane-bound transcription factor site-2 protease, also known as S2P endopeptidase or site-2 protease (S2P), is an enzyme encoded by the MBTPS2 gene which liberates the N-terminal fragment of sterol regulatory element-binding protein (SREBP) transcription factors from membranes. S2P cleaves the transmembrane domain of SREPB, making it a member of the class of intramembrane proteases.
Insulin induced gene 1, also known as INSIG1, is a protein which in humans is encoded by the INSIG1 gene.
Insulin induced gene 2, also known as INSIG2, is a protein which in humans is encoded by the INSIG2 gene.
YWTD repeats are four-stranded beta-propeller repeats found in low-density lipoprotein receptors (LDLR). The six YWTD repeats together fold into a six-bladed beta-propeller. Each blade of the propeller consists of four antiparallel beta-strands; the innermost strand of each blade is labeled 1 and the outermost strand, 4. The sequence repeats are offset with respect to the blades of the propeller, such that any given 40-residue YWTD repeat spans strands 24 of one propeller blade and strand 1 of the subsequent blade. This offset ensures circularization of the propeller because the last strand of the final sequence repeat acts as an innermost strand 1 of the blade that harbors strands 24 from the first sequence repeat. The repeat is found in a variety of proteins that include, vitellogenin receptor from Drosophila melanogaster, low-density lipoprotein (LDL) receptor, preproepidermal growth factor, and nidogen (entactin).
Sandip Kumar Basu is an Indian molecular biologist and the holder of the J. C. Bose Chair of the National Academy of Sciences, India, who is credited with innovations in the treatment protocols of leishmaniasis, tuberculosis, viral infections, multidrug resistant cancer and arterosclerosis. He was honored by the Government of India, in 2001, with the fourth highest Indian civilian award of Padma Shri.
