User:Morgan Bertolino/Sandbox 2
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== Background == | == Background == | ||
<StructureSection load='2x4d' size='340' side='right' caption='Crystal structure of human phospholysine phosphohistidine inorganic pyrophosphate phosphatase' scene=''> | <StructureSection load='2x4d' size='340' side='right' caption='Crystal structure of human phospholysine phosphohistidine inorganic pyrophosphate phosphatase' scene=''> | ||
| - | Phospholysine phosphohistidine inorganic pyrophosphate phosphatase | + | Phospholysine phosphohistidine inorganic pyrophosphate phosphatase <scene name='84/842888/Lhpp/1'>(LHPP)</scene> is a hydrolase enzyme which is known to be expressed in the liver, kidney, and at moderate levels in the brain<ref name=Gohla>DOI: 10.1016/j.bbamcr.2018.07.007</ref>. It belongs to the haloacid dehalogenase (HAD) superfamily of hydrolases with hydrolyze a wide variety of substrates<ref name=Seifried>DOI: 10.1111/j.1742-4658.2012.08633.x</ref>. LHPP, specifically, hydrolyzes both oxygen-phosphorous bonds in inorganic phosphate and nitrogen-phosphorous bonds in 6-phospholysine, 3-phosphohistidine, and imidodiphosphate. LHPP has been of particular interest to researchers in recent years due to its hypothesized function as a tumor suppressor and thus its role in various cancers<ref name=Hindupur>DOI: 10.1038/nature26140</ref>. |
== The HAD Superfamily == | == The HAD Superfamily == | ||
| - | The haloacid dehalogenase superfamily contains over 79,000 unique sequences of enzymes and is largely made up of enzymes that catalyze phosphoryl transfer<ref name=Gohla/>. | + | The haloacid dehalogenase superfamily contains over 79,000 unique sequences of enzymes and is largely made up of enzymes that catalyze phosphoryl transfer<ref name=Gohla/>. <scene name='84/842888/Calcineurin/1'>Phosphatases</scene> (phosphate monoester hydrolases) make up the majority of these enzymes at ~79%, with many of the rest being <scene name='84/842888/Atp_synthase/1'>ATPases</scene> (phosphoanhydride hydrolases)<ref name=Seifried/>. While many members of the enzyme family are found predominantly in prokaryotes, 183 human HAD enzymes have been identified, with at least 40 HAD-type phosphatases. This ancient group of enzymes has evolved over time to dephosphorylate a wide variety of substituents including carbohydrates, lipids, DNA, and various amino acid-phosphorylated proteins in humans, though many target small metabolites in intermediary metabolic reactions. These enzyme were originally thought to carry out simple regulatory tasks, but recent research has shown that some of these enzymes play roles in various genetic disorders<ref name=Gohla/>. |
| - | Sequentially, there is very low similarity across the HAD phosphatases, so members of the family are instead identified using alignments of amino acid sequences that are based on the presence of | + | Sequentially, there is very low similarity across the HAD phosphatases, so members of the family are instead identified using alignments of amino acid sequences that are based on the presence of four short signature motifs that contain conserved catalytic residues present in HAD enzymes. Another similarity between the HAD phosphatase superfamily is that all the enzymes share the same active core structural arrangement, consisting of catalytic machinery residues positioned in a Rossmann fold. This super-secondary structure is characterized by an alternating motif of repeating β-α units arranged in three stacked α/β sandwiches. The Rossmann fold of HAD phosphatases also contains three unique structural signatures including the squiggle, flap, and cap domains. These domains allow HAD phosphatases to form different conformational states as well as influence substrate specificity<ref name=Seifried/>. |
== HAD Phosphatases: Mechanism & Structure == | == HAD Phosphatases: Mechanism & Structure == | ||
| - | The catalysis mechanism of HAD phosphatases is unique in comparison to other phosphatases and requires the use of an | + | The catalysis mechanism of HAD phosphatases is unique in comparison to other phosphatases and requires the use of an aspartate residue in the <scene name='84/842888/Binding_residues/1'>active site</scene>. This residue facilitates a nucleophilic attack and also contributes to these enzymes' lack of sensitivity to common phosphatase inhibitors. This attack is carried out in a two-step phosphoaspartyl transferase mechanism. As previously mentioned, the aspartate residue initiates the nucleophilic attack on the substrate's phosphoryl group, displacing the substrate's leaving group and forming a phosphoaspartyl enzyme intermediate. In the second step, a water molecule initiates a nucleophilic attack on the previously formed intermediate, releasing free phosphate and regenerating the aspartate catalyst. There is also a second Asp residue, designate Asp + 2, which functions as a general acid/base to protonate the leaving group of the substrate in the first reaction and deprotonate the water molecule in the second reaction<ref name=Seifried/>. |
| - | It is also important to mention that all HAD phosphoaspartyl transferases require | + | It is also important to mention that all HAD phosphoaspartyl transferases require <scene name='84/842888/Mg2/1'>Mg2+</scene> as an obligatory cofactor. This cofactor has multiple functions, including positioning of the substrate phosphoryl group in relation to the Asp nucleophile, providing electrostatic stabilization and charge neutralization in the transition state<ref name=Seifried/>. |
== LHPP-Specific Mechanisms & Structure == | == LHPP-Specific Mechanisms & Structure == | ||
| - | LHPP is a phosphoramidase that forms a homodimer in solution and is involved in the cleavage of P-N and O-P bonds. This protein contains a Ser residue where other members of the HAD family contain Asp or Thr residues. It also contains a Ser + 2 residue, which is unique to mammalian HAD-type hydrolases. LHPP is a capped HAD phosphatase (meaning it contains a cap domain) with a | + | LHPP is a phosphoramidase that forms a homodimer in solution and is involved in the cleavage of P-N and O-P bonds. This protein contains a Ser residue where other members of the HAD family contain Asp or Thr residues. It also contains a Ser + 2 residue, which is unique to mammalian HAD-type hydrolases. LHPP is a capped HAD phosphatase (meaning it contains a cap domain) with a C2a-type cap domain. Cap domains of HAD phosphatases are integral to controlling access to the active site via shielding and determining substrate specificity. Some capped HAD phosphatases, like LHPP, are able to act on <scene name='84/842888/Phosphoprotein/1'>phosphoproteins</scene> in addition to their other functions. This is particularly interesting due to the occluded nature of the active sites of phosphoproteins, making them difficult to access. LHPP, along with other C2a-capped HAD phosphatases, has been shown to act on serine-, tyrosine-, and histidine-phosphorylated proteins. The subcellular localization of LHPP is currently unknown, but proposed locations are the nucleus and cytosol. The enzyme is also predicted to interact with ATP synthase subunits and theorized to play a role in oxidative phosphorylation<ref name=Gohla/>. |
== Role in Disease == | == Role in Disease == | ||
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'''Thyroid Diseases''' | '''Thyroid Diseases''' | ||
| - | One study has implicated increased nuclear expression of LHPP in association with hyperthyroidism, though it is unclear is these results have since been replicated. This study looked at the intranuclear expression of LHPP thyrocytes and showed enhanced expression in Graves' disease, though it concluded that LHPP expression may not actually be regulated by disease-derived serum factors. | + | One study has implicated increased nuclear expression of LHPP in association with hyperthyroidism, though it is unclear is these results have since been replicated. This study looked at the intranuclear expression of LHPP thyrocytes and showed enhanced expression in Graves' disease, though it concluded that LHPP expression may not actually be regulated by disease-derived serum factors<ref>DOI: 10.1016/j.bbrc.2006.01.016</ref>. |
== References == | == References == | ||
<references/> | <references/> | ||
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