Monoglyceride lipase: Difference between revisions

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-==Monoglyceride Lipase (MGL)==
 <StructureSection load='' size='450' side='right' scene='57/573133/Generic_monomer/3' caption='Monoglyceride Lipase (PDB ID [[3PEK]])'>
-[[Image:Complete_crystal_structure.png|left|300px|thumb|'''Figure 1:'''Crystal Structure of MGL Alpha helixes are in blue and beta sheets in purple. This protein is a dimer that is linked by antiparallel beta sheets]]
+[[Image:Complete_crystal_structure.png|left|300px|thumb|'''Figure 1:'''Crystal Structure of MGL (α-helixes are in blue and β-sheets in purple). MGL is a dimer that is linked by antiparallel beta sheets]]
 ==Introduction==
 '''Monoglyceride Lipase''' ('''MGL''', '''MAGL''', '''MGLL''') is a 33 kDa [http://en.wikipedia.org/wiki/Protein protein] <ref name="labar"> PMID:19957260 </ref> found mostly in the cell membrane (<scene name='57/573133/Generic_monomer/3'>default view</scene>). MGL is a [http://en.wikipedia.org/wiki/Serine_hydrolase serine hydrolase] enzyme that contains an [http://en.wikipedia.org/wiki/Alpha/beta_hydrolase_fold α/β hydrolase fold]. MGL plays a key role in the hydrolysis of [http://en.wikipedia.org/wiki/2-Arachidonoylglycerol 2-arachidonoylglycerol] (2-AG), an endocannabinoid produced by the the central nervous system.<ref name="labar" /><ref name="bert"> PMID:19962385 </ref><ref name="shalk"> PMID:21308848 </ref><ref name="blank"> PMID:18096503 </ref> The hydrolase fold, along with a characteristic [http://en.wikipedia.org/wiki/Amphiphile amphipathic] occluded tunnel, allows MGL's active site to selectively bind to 2-AG and [http://www.biologie.uni-freiburg.de/data/bio2/schroeder/Chemical_Structures/Anandamide.gif degrade it] into [http://en.wikipedia.org/wiki/Arachidonic_acid arachidonic acid] and glycerol.<ref name="bert" /> 2-AG has been found to possess anti-nociceptive, immunomodulatory, anti-inflammatory and tumor-reductive character when it binds to cannabinoid receptors. <ref name="labar" /> <ref name="bert"/> Due to the vast medical and therapeutic utility of 2-AG, the inhibition of MGL is a high interest target in pharmaceutical research.   Furthermore, MGL has also been cited as having both negative and positive effector roles in cancer pathology. <ref name="nomura"> PMID:21802006 </ref> <ref name="hong"> PMID:22349814 </ref>
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 ===Catalytic Triad===
-MGL’s serine hydrolase chemistry is executed by a <scene name='57/573134/Catalytic_triad/4'>Catalytic Triad</scene> (Ser132-His279-Asp249) and seems to utilize the same mechanism as the much-studied [http://en.wikipedia.org/wiki/Chymotrypsin chymotrypsin]. In this mechanism, an activated serine nucleophile cleaves the ester bond of the substrate.<ref name="labar" /><ref name="bert" /><ref name="shalk" /> The subsequent tetrahedral intermediate is stabilized by the <scene name='57/573134/Oxyanion_hole/3'>Oxyanion Hole</scene>, formed by the main-chain nitrogens of Ala61 and Met (or Se-Met) 133.<ref name="bert" />
+MGL’s serine hydrolase chemistry is executed by a <scene name='57/573134/Catalytic_triad/4'>Catalytic Triad</scene> (Ser132-His279-Asp249) and seems to utilize the same mechanism as the much-studied [http://en.wikipedia.org/wiki/Chymotrypsin chymotrypsin]. In this mechanism, an activated serine nucleophile cleaves the ester bond of the substrate.<ref name="labar" /><ref name="bert" /><ref name="shalk" /> The subsequent tetrahedral intermediate is stabilized by the <scene name='57/573134/Oxyanion_hole/3'>Oxyanion Hole</scene>, formed by the main-chain nitrogens of Ala61 and Met (or Se-Met) 133.<ref name="bert" /> The triad was found using site-directed mutagenesis of each individual residue and each of these amino acid residues are catalytically essential to MGL <ref name="Bertrand" />. The catalytic triad is located in the [[:Category:Ligand binding pocket| Binding Pocket]] buried at the bottom of it in the oxyanion hole connected by a water molecule.'''Figure 4''' [[Image:Catalytic_triad_binding_pocket.png|300px|thumb|'''Figure 4:''' The binding pocket of MGL with the catalytic triad (shown in red) buried in it.]]
+===Ligand Binding Site===
+[[Image:Overall_ligand.png|left|200px|thumb|'''Figure 6:''' Ligand within the Overall Structure of MGL]] [[Image:Ligand_tunnel.png|right|200px|thumb|'''Figure 7:''' Ligand binding pocket showing the hydrophobic and polar regions]]
+The <scene name='58/580298/Ligand/1'>ligand binding pocket</scene> of MGL has a large hydrophobic region with a polar bottom.  The entrance of the binding pocket for MGL contains a lid, which is very flexible <ref name="Bertrand" />.  The binding pocket or tunnel within MGL matches with the overall structure of 2-AG, with 2-AG's polar head being cleaved by the catalytic triad '''Figure 7'''. The binding pocket is not being adjusted to the ligand's shape.  However, the main movements of MGL involve the lid region of the ligand binding pocket upon the ligand binding. When 2-AG and its isomer 1(3)-AG bind to MGL, the hydrophobic chain is first aligned with the left part of the binding pocket. The carbonyl on 2-AG and 1(3)-AG is then hydrogen bonded to <scene name='58/580298/Ala61/1'>Ala61</scene>. The polar head group of the ligand is then fixed by three hydrogen bonds.   The large lipophilic portion of the binding pocket is being used to design more selectivie inhibitors <ref name="Bertrand" />.
 ==Biological/Medical Relevance==
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 ===MGL Inhibitors===
-Three general MGL [http://en.wikipedia.org/wiki/Enzyme_inhibitor inhibitor] classes have been observed: noncompetitive, partially irreversible inhibitors such as [http://en.wikipedia.org/wiki/URB602 URB602]; cysteine-reactive inhibitors such as [http://www.chemspider.com/Chemical-Structure.24774833.html N-arachidonoylmaleimide] (NAM); and irreversible serine-reactive inhibitors such as [http://en.wikipedia.org/wiki/JZL184 JZL184] and <scene name='57/573134/Sar629/3'>SAR 629</scene>.<ref name="bert" /> SAR629 covalently binds to the catalytic Serine-132; the oxygen of the nucleophilic serene residue attacks the carbonyl carbon of SAR629, forming a [http://en.wikipedia.org/wiki/Carbamate carbamate]. This covalent bond is believed to be reversible via hydrolysis, albeit slowly.<ref name="bert" /> Due to JZL184's similar structure to SAR629, it may undergo a similar reaction with MGL.<ref name="bert" /> Despite the existence of multiple lead compounds, there is a strong demand for the creation of more highly-specific and more potent inhibitors that could be used as anti-pain drugs for their ability to keep 2-AG active in the neuronal synapses. <ref name="labar" />
+Three general MGL [http://en.wikipedia.org/wiki/Enzyme_inhibitor inhibitor] classes have been observed: noncompetitive, partially irreversible inhibitors such as [http://en.wikipedia.org/wiki/URB602 URB602]; cysteine-reactive inhibitors such as [http://www.chemspider.com/Chemical-Structure.24774833.html N-arachidonoylmaleimide] (NAM); and irreversible serine-reactive inhibitors such as [http://en.wikipedia.org/wiki/JZL184 JZL184] and <scene name='57/573134/Sar629/3'>SAR 629</scene>.<ref name="bert" /> SAR629 covalently binds to the catalytic Serine-132; the oxygen of the nucleophilic serene residue attacks the carbonyl carbon of SAR629, forming a [http://en.wikipedia.org/wiki/Carbamate carbamate]. This covalent bond is believed to be reversible via hydrolysis, albeit slowly.<ref name="bert" />SAR629 adopts a Y shape and interacts with the MGL by hydrophobic interactions, with a few polar interactions as well. '''Figure 3''' [[Image:SAR.png|left|thumb|'''Figure 3:''' The structure and shape of SAR629.]] Due to JZL184's similar structure to SAR629, it may undergo a similar reaction with MGL.<ref name="bert" /> Despite the existence of multiple lead compounds, there is a strong demand for the creation of more highly-specific and more potent inhibitors that could be used as anti-pain drugs for their ability to keep 2-AG active in the neuronal synapses. <ref name="labar" />
+N-arachidonyl maleimide (NAM) is another inhibitor of MGL. NAM reacts with the amino acid <scene name='58/580298/Cys252/1'>Cys252</scene>. '''Figure 2''' [[Image:NAM.png|thumb|'''Figure 2:''' The structure of N-arachidonyl maleimide (NAM)that interacts with Cys252.]] Cys252 is buried in the active site near the catalytic serine and functions by sterically clashing with the natural ligand. A possible conformational change to Cys252 upon the binding of NAM could also lead to an inactive form of MGL.
 ===Cancer Relevance===
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 MGL’s role in different body tissues is an ongoing area of research aimed at elucidating its complex role in cancer pathology. MGL’s effect on exogenous cannabinoid medications that are administered to cancer patients as a palliative medication is of particular scientific interes. <ref name="nomura" />
-===Inhibition of MGL===
-The importance of [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2013872/ Inhibition] of Monoglyceride lipase is to keep it from breaking down 2-arachidonoyl glycerol. When 2-Ag is broken down it is not able to suppress pain and depression brain functions that human beings experience. N-arachidonyl maleimide (NAM) is one inhibitor of MGL that reacts with the amino acid <scene name='58/580298/Cys252/1'>Cys252</scene>. '''Figure 2'''
-[[Image:NAM.png|thumb|'''Figure 2:''' The structure of N-arachidonyl maleimide (NAM)that interacts with Cys252.]]
-This Cysteine is buried in the active site near the catalytic serine and functions by sterically clashing with the natural ligand. A possible conformational change to Cys252 upon the binding of NAM could also lead to an inactive form of MGL.
-MGL is also inhibited by being in complex with <scene name='58/580298/Sar629/2'>SAR629</scene> that is covalently bound to the catalytic Ser132. SAR629 adopts a Y shape and interacts with the MGL by hydrophobic interactions, with a few polar interactions as well. '''Figure 3'''
-[[Image:SAR.png|left|thumb|'''Figure 3:''' The structure and shape of SAR629.]]
-With SAR629 interacting with the catalytic triad it inhibits the triad from breaking down 2-AG and inactivates MGL <ref name="Bertrand" />
-==Structure==
-The <scene name='58/580298/Overall_structure/3'>overall structure</scene> of MGL has an eight-stranded β-sheet protein fold with seven parallel and one <scene name='58/580299/Beta_sheets/1'> antiparallel strand </scene>. Similar to the other α/β hydrolases, the β-sheets in the center of the protein surrounded by α-helices.  The combination of the α-helices and β-sheets are able to provide a stable scaffold for the active site within MGL.  MGL is monomeric.  The catalytic triad, containing Ser132, His279, and Asp249, is found at the bottom of the binding pocket <ref name="Bertrand" />.
-== Catalytic triad ==
-MGL has a classic <scene name='58/580298/Catalytic_triad/4'>catalytic triad</scene> that contains Ser-His-Asp. The triad was found using site-directed mutagenesis of each individual residue and each of these amino acid residues are catalytically essential to MGL <ref name="Bertrand" />. The catalytic triad is located in the [[:Category:Ligand binding pocket| Binding Pocket]] buried at the bottom of it in the oxyanion hole connected by a water molecule.'''Figure 4'''
-[[Image:Catalytic_triad_binding_pocket.png|300px|thumb|'''Figure 4:''' The binding pocket of MGL with the catalytic triad (shown in red) buried in it.]]
-This triad has a natural attraction to Endocannabinoids, specifically 2-arachidonylglycerol (2-AG) <ref name="Bertrand" />.
-====Binding====
--AG binds to the catalytic triad and is hydrolyzed. The structure of 2-AG contains a long and flexible aliphatic chain and a polar head that is cleaved. It is the polar head that gets attracted to the catalytic triad and binds to it so the catalytic Serine can cleave 2-AG. 2-AG is broken down into arachidonic acid and glycerol which makes 2-AG inactive<ref name="Bertrand" />. '''See Overall Reaction.'''
-===Inhibition of Catalytic Triad===
-Research on MGL is being geared towards inhibiting 2-AG from binding to the catalytic triad and being hydrolyzed. The binding of 2-AG to the catalytic triad can be extracted before being hydrolyzed. MPD (2-methyl-pentane-2,4-diol)is located at the end of the tunnel where the catalytic triad is at and the tunnel is filled with MPD molecules. MPD being in the same vicinity will extract 2-AG from the triad and the MPD molecule will sit in there in place of 2-AG. This is a natural inhibition phenomenon. Inhibition of MGL leads to increase in 2-AG levels since AG is broken down by MGL <ref name="Clemente" />. The catalytic triad is a major part of MGL and its interaction with other parts within the brain and how the brain functions.
-===Overall Reaction===
-[[Image:Reaction.PNG|350px|thumb|'''Figure 5:''' The breakdown of 2-AG into arachidonic acid +glyverol by MGL.]]
-In this reaction 2-AG binds to the catalytic triad in the oxyanion hole in the active site. In the [[:Category:Oxyanion hole| oxyanion holes]] the substrate is stabilized by two nitrogen atoms from the catalytic  Histidine and Aspartate during the transition step of the catalytic reaction. The catalytic triad activates the nucleophilic serine and cleaves the ester bond of 2-AG that is being stabilized by its carbonyl group that is attached to the oxyanion hole. The glycerol molecule is released and it might diffuse to the narrow "exit hole", while the arachidonic acid would diffuse back to the top of the tunnel and leave the protein <ref name="Bertrand" />.
-==Ligand Binding Site==
-[[Image:Overall_ligand.png|left|200px|thumb|'''Figure 6:''' Ligand within the Overall Structure of MGL]] [[Image:Ligand_tunnel.png|right|200px|thumb|'''Figure 7:''' Ligand binding pocket showing the hydrophobic and polar regions]]
-The <scene name='58/580298/Ligand/1'>ligand binding pocket</scene> of MGL has a large hydrophobic region with a polar bottom.  The entrance of the binding pocket for MGL contains a lid, which is very flexible <ref name="Bertrand" />.  The binding pocket or tunnel within MGL matches with the overall structure of 2-AG, with 2-AG's polar head being cleaved by the catalytic triad '''Figure 7'''. The binding pocket is not being adjusted to the ligand's shape.  However, the main movements of MGL involve the lid region of the ligand binding pocket upon the ligand binding. When 2-AG and its isomer 1(3)-AG bind to MGL, the hydrophobic chain is first aligned with the left part of the binding pocket. The carbonyl on 2-AG and 1(3)-AG is then hydrogen bonded to <scene name='58/580298/Ala61/1'>Ala61</scene>. The polar head group of the ligand is then fixed by three hydrogen bonds.   The large lipophilic portion of the binding pocket is being used to design more selectivie inhibitors <ref name="Bertrand" />.
 == References ==