User:Giselle Flores/Sandbox 1
From Proteopedia
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==Introduction== | ==Introduction== | ||
| - | <scene name='87/877513/Original_scene/1'>Lipoprotein Lipase</scene>(LPL) is an important enzyme for the breakdown of triglycerides in the body (Figure 1). [[Image:Simple_mech.png|400 px|right|thumb|Figure 1: Purpose of LPL: catalyze the breakdown of a triglyceride into a diglyceride and create one free fatty acid]] A [https://en.wikipedia.org/wiki/Lipase lipase] is an enzyme that is capable of catalyzing the [https://en.wikipedia.org/wiki/Hydrolysis hydrolysis] of fats/lipids which are consumed through oils. It is encoded by the [https://www.genecards.org/cgi-bin/carddisp.pl?gene=LPL p22 region in chromosome 8]. Once synthesized, it is secreted into the interstitial space in several tissues. The main site of action for <scene name='87/877513/Original_scene/1'>LPL</scene> is in the [https://www.pnas.org/content/pnas/116/5/1480/F1.large.jpg capillary lumen] within muscle and adipose tissues. The function of this lipase is to hydrolyze [https://en.wikipedia.org/wiki/Triglyceride triglycerides] of very low density lipoproteins ([https://qph.fs.quoracdn.net/main-qimg-8e874e647baeb69b00203c47165247e2 VLDL]) and to aid in the delivery of lipid nutrients to vital tissues. The enzyme is commonly found on the surface of cells that line blood capillaries. Two different lipoproteins are essential to break down triglycerides. One of the lipoproteins is utilized to transport fat into the bloodstream from different organs. The lipoproteins essential, in the transport of fat from the intestine are referred to as [https://en.wikipedia.org/wiki/Chylomicron chylomicrons]. VLDL | + | <scene name='87/877513/Original_scene/1'>Lipoprotein Lipase</scene>(LPL) is an important enzyme for the breakdown of triglycerides in the body (Figure 1). [[Image:Simple_mech.png|400 px|right|thumb|Figure 1: Purpose of LPL: catalyze the breakdown of a triglyceride into a diglyceride and create one free fatty acid]] A [https://en.wikipedia.org/wiki/Lipase lipase] is an enzyme that is capable of catalyzing the [https://en.wikipedia.org/wiki/Hydrolysis hydrolysis] of fats/lipids which are consumed through oils. It is encoded by the [https://www.genecards.org/cgi-bin/carddisp.pl?gene=LPL p22 region in chromosome 8]. Once synthesized, it is secreted into the interstitial space in several tissues. The main site of action for <scene name='87/877513/Original_scene/1'>LPL</scene> is in the [https://www.pnas.org/content/pnas/116/5/1480/F1.large.jpg capillary lumen] within muscle and adipose tissues. The function of this lipase is to hydrolyze [https://en.wikipedia.org/wiki/Triglyceride triglycerides] of very low-density lipoproteins ([https://qph.fs.quoracdn.net/main-qimg-8e874e647baeb69b00203c47165247e2 VLDL]) and to aid in the delivery of lipid nutrients to vital tissues. The enzyme is commonly found on the surface of cells that line blood capillaries. Two different lipoproteins are essential to break down triglycerides. One of the lipoproteins is utilized to transport fat into the bloodstream from different organs. The lipoproteins essential, in the transport of fat from the intestine, are referred to as [https://en.wikipedia.org/wiki/Chylomicron chylomicrons]. VLDL is utilized in carrying triglycerides from the liver into the bloodstream. The hydrolysis of triglycerides by lipoprotein lipase results in fat molecules being used by the body as energy or stored in fatty tissue. |
==Structural Overview== | ==Structural Overview== | ||
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=== GPIHBP1 === | === GPIHBP1 === | ||
| - | Glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 ([https://en.wikipedia.org/wiki/GPIHBP1 GPIHBP1]) is a secondary domain that is critical to the stabilization, function, and movement of <scene name='87/877513/Original_scene/1'>LPL</scene>. The GPIHBP1’s highly acidic and intrinsically disordered N-terminal domain | + | Glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 ([https://en.wikipedia.org/wiki/GPIHBP1 GPIHBP1]) is a secondary domain that is critical to the stabilization, function, and movement of <scene name='87/877513/Original_scene/1'>LPL</scene>. The GPIHBP1’s highly acidic and intrinsically disordered N-terminal domain is essential to the binding of LPL’s C-terminal Domain. It has been shown that GPIHBP1 has three “finger” domains, which hold it tightly to LPL by <scene name='87/877513/Hydrophobic_interface-labeled/3'>hydrophobic interactions</scene>. The importance of GPIBP1’s affinity to LPL was analyzed by Birrane et al.<ref name=”Birrane”>PMID:30559189</ref>, and it was found that missense mutations of critical residues resulted in high amounts of impairments. It was also concluded that these impairments caused different profound diseases. |
== Structural Highlights == | == Structural Highlights == | ||
=== Calcium Ion Stabilization === | === Calcium Ion Stabilization === | ||
| - | Ions are widely used in proteins and | + | Ions are widely used in proteins and mechanistic stabilization in many areas of biochemistry. LPL’s tertiary folding is stabilized by a Calcium (Ca2+) ion. The calcium ion shares electron density with surrounding residues in order to orient the protein in its formal state. The <scene name='87/877513/Calcium_stabilization_-labeled/2'>calcium ion stabilization</scene> is achieved by the calcium ion’s interactions with the following of LPL’s residues: Ala194, Arg197, Ser199, Asp201, and Asp202. |
=== Lid and Lipid Binding Region === | === Lid and Lipid Binding Region === | ||
| - | In the presence of the GPIHBP1 inhibitor, the <scene name='87/877514/Lid_region_final/1'>Lid Region</scene> and lipid binding region become visible within the structure. As displayed through a study conducted by Arora et. al, in 2019, the lipid binding region of LPL actively interacts with the known inhibitor in the dimeric form. <ref name=”Arora”>PMID:31072929</ref> This was established to be the only time that the homodimeric form was shown as an active lipase. The lid region residues Ile245, Ile249, V251, Ile252, Leu257, Val260, Leu263, and Val264, is found as an open conformation | + | In the presence of the GPIHBP1 inhibitor, the <scene name='87/877514/Lid_region_final/1'>Lid Region</scene> and lipid binding region become visible within the structure. As displayed through a study conducted by Arora et. al, in 2019, the lipid-binding region of LPL actively interacts with the known inhibitor in the dimeric form. <ref name=”Arora”>PMID:31072929</ref> This was established to be the only time that the homodimeric form was shown as an active lipase. The lid region residues Ile245, Ile249, V251, Ile252, Leu257, Val260, Leu263, and Val264, is found as an open conformation that is composed of two small alpha helices that reach out and away from the protein. The lid and lipid-binding region create hydrophobic patches on the surface of lipoprotein lipase which are essential for <scene name='87/877514/Lipid_binding_and_lid/1'>ligand binding</scene> by LPL. |
| - | [[Image:Inhibiting.png|300 px|right|thumb|The novel inhibitor bound between lipid binding region of one LPL monomer and the catalytic site of the other LPL monomer in the homodimeric form.]] | + | [[Image:Inhibiting.png|300 px|right|thumb|The novel inhibitor bound between the lipid-binding region of one LPL monomer and the catalytic site of the other LPL monomer in the homodimeric form.]] |
==Mechanism== | ==Mechanism== | ||
| - | Lipoprotein Lipase functions to catalyze the hydrolysis of one [https://en.wikipedia.org/wiki/Ester ester bond] of triglycerides in order to remove one fatty acid tail and turn the triglyceride into a diglyceride. It does this by utilizing a simple [https://en.wikipedia.org/wiki/Serine_hydrolase serine hydrolase] mechanism, in which it uses a <scene name='87/877513/Catalytic_triad-1/6'>catalytic triad</scene> composed of Asp183, His268, and Ser159 to catalyze the hydrolysis. His268 serves as a base catalyst by deprotonation of Ser159, which can then serve as the [https://en.wikipedia.org/wiki/Nucleophile nucleophile]. The transition state of the catalysis is stabilized by the backbone of Trp82 and Leu160 residues, forming the <scene name='87/877513/Oxyanion_hole_-_labeled/8'>oxyanion hole</scene> (Figure 2). The hydrolysis results in the formation of one free fatty acid and | + | Lipoprotein Lipase functions to catalyze the hydrolysis of one [https://en.wikipedia.org/wiki/Ester ester bond] of triglycerides in order to remove one fatty acid tail and turn the triglyceride into a diglyceride. It does this by utilizing a simple [https://en.wikipedia.org/wiki/Serine_hydrolase serine hydrolase] mechanism, in which it uses a <scene name='87/877513/Catalytic_triad-1/6'>catalytic triad</scene> composed of Asp183, His268, and Ser159 to catalyze the hydrolysis. His268 serves as a base catalyst by deprotonation of Ser159, which can then serve as the [https://en.wikipedia.org/wiki/Nucleophile nucleophile]. The transition state of the catalysis is stabilized by the backbone of Trp82 and Leu160 residues, forming the <scene name='87/877513/Oxyanion_hole_-_labeled/8'>oxyanion hole</scene> (Figure 2). The hydrolysis results in the formation of one free fatty acid and glycerol with two fatty acid tails. |
[[Image:LPL_final_Mechanism.png|600 px|center|thumb|Figure 2: Serine hydrolase mechanism utilized by LPL to catalyze the breakdown of one ester bond of a triglyceride. Compounds colored red are the products of the hydrolysis.]] | [[Image:LPL_final_Mechanism.png|600 px|center|thumb|Figure 2: Serine hydrolase mechanism utilized by LPL to catalyze the breakdown of one ester bond of a triglyceride. Compounds colored red are the products of the hydrolysis.]] | ||
== Relevance & Disease == | == Relevance & Disease == | ||
| - | LPL is an extremely important enzyme, in that it is responsible for the proper breakdown of certain fats in the body. LPL breaks down triglycerides carried in chylomicrons, otherwise known as very low-density lipoproteins ([https://en.wikipedia.org/wiki/Very_low-density_lipoprotein VLDL]). Chylomicrons carry digested fats in the form of triglycerides out of the small intestine and into the bloodstream. LPL recognizes the chylomicrons, and hydrolyzes the associated triglycerides.<ref name=”Kersten”>PMID:24721265</ref> When triglycerides are not broken down properly and are allowed to build up, they can lead to increased plasma triglyceride levels ([https://en.wikipedia.org/wiki/Hypertriglyceridemia hypertriglyceridemia]) and [https://en.wikipedia.org/wiki/Cholesterol cholesterol] buildup. Hypertriglyceridemia is very unhealthy and is the leading cause of [https://my.clevelandclinic.org/health/diseases/16898-coronary-artery-disease Coronary Artery Disease] in America.<ref name=”Austin”>PMID:9526807</ref> Cholesterol buildup is caused by excess fats (triglycerides) and is a similarly serious issue with regards to obesity and heart disease in the United States as it can lead to plaque buildup in arteries and veins, which restricts blood flow.<ref name=”Kruth”>PMID:11899253</ref> [https://medlineplus.gov/ency/article/000405.htm Chylomicronemia], which is defined as an excess of chylomicrons in the blood, is the disease characterized by the body being deficient in LPL resulting in persistent hypertriglyceridemia. This disease causes the body to be unable to digest very much ingested fats | + | LPL is an extremely important enzyme, in that it is responsible for the proper breakdown of certain fats in the body. LPL breaks down triglycerides carried in chylomicrons, otherwise known as very-low-density lipoproteins ([https://en.wikipedia.org/wiki/Very_low-density_lipoprotein VLDL]). Chylomicrons carry digested fats in the form of triglycerides out of the small intestine and into the bloodstream. LPL recognizes the chylomicrons, and hydrolyzes the associated triglycerides.<ref name=”Kersten”>PMID:24721265</ref> When triglycerides are not broken down properly and are allowed to build up, they can lead to increased plasma triglyceride levels ([https://en.wikipedia.org/wiki/Hypertriglyceridemia hypertriglyceridemia]) and [https://en.wikipedia.org/wiki/Cholesterol cholesterol] buildup. Hypertriglyceridemia is very unhealthy and is the leading cause of [https://my.clevelandclinic.org/health/diseases/16898-coronary-artery-disease Coronary Artery Disease] in America.<ref name=”Austin”>PMID:9526807</ref> Cholesterol buildup is caused by excess fats (triglycerides) and is a similarly serious issue with regards to obesity and heart disease in the United States as it can lead to plaque buildup in arteries and veins, which restricts blood flow.<ref name=”Kruth”>PMID:11899253</ref> [https://medlineplus.gov/ency/article/000405.htm Chylomicronemia], which is defined as an excess of chylomicrons in the blood, is the disease characterized by the body being deficient in LPL resulting in persistent hypertriglyceridemia. This disease causes the body to be unable to digest very much ingested fats and often leads to severe abdominal discomfort and several episodes of acute pancreatitis.<ref name=”Francis”>PMID:11905095</ref> In short, without LPL in the body, triglycerides are unable to get broken down, and there is a much higher likelihood of developing coronary & metabolic based diseases. |
===M404 Mutation=== | ===M404 Mutation=== | ||
| - | A mutation that is believed to cause chylomicronemia is known as M404R. Within this mutation, the methionine | + | A mutation that is believed to cause chylomicronemia is known as <scene name='87/877514/M404_mutation_site/1'>M404R</scene>. Within this mutation, the methionine is replaced with a large and hydrophilic arginine. While this mutation does not impact LPL secretion, it does affect the formation of the LPL-GPIHBP1 complex. This mutation is known to impact LPL’s interaction with GPIHB1’s V121, E122, T124, and V126 residues. Given that the arginine disrupts the original stabilization of this complex, its occurrence disrupts the binding of the LPL-GPIHBP1 complex. |
Revision as of 22:17, 27 April 2021
Lipoprotein Lipase coupled with GPIHBP1
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