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| - | == Human protein phosphatase 2C == | + | <table width="95%" border="0"><tr><td> |
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| - | <Structure load='2IQ1' size='350' frame='true' align='right' caption='Quartenary structure of human protein phosphatase PP2Cm with Mg(II) (PDB ID 4DA1)' scene='Insert optional scene name here' /> Protein Phosphatases 2C are essencial enzymes involved in the regulation of several signaling pathways of branched-chain α-ketoacid dehydrogenase complex (BCKDC) by phosphorylation/dephosphorylation. The PP2C Family are Mg<sup>2+</sup> and Mn<sup>2+</sup> dependent monomeric proteins with two characteristic structural domains: a catalytic domain N-terminal with six alpha-helices, and a C-terminal region with three alpha-helices. The multienzyme complex uses numerous copies of three enzymes as major building blocks E1, E2 and E3. A dihydrolipoyl transacylase (E2) forms the core of the complex with 24 copies in octahedral symmetry. | + | <span style="font-size:160%"><b>Structural basis for regulation of rhizobial nodulation and symbiosis gene expression by the regulatory protein NolR </b></span> |
| - | The human branched-chain α-ketoacid dehydrogenase complex ser/thr phosphatase, PP2Cm, (BDP) is attached to the E2 core through non-covalent bonds. PP2Cm is distinguished from other groups of phosphatases by its structural distinction, absolute requirement for divalent cation, the <scene name='32/32/Protein_pp2cm_with_mgii/7'>beta-sheet sandwich</scene> catalytic domain and shows Mn<sup>2+</sup>/Mg<sup>2+</sup> dependent phosphatase activity. PP2Cm structure has two central antiparallel beta sheets that are flanked by alpha helices and the <scene name='32/32/Protein_pp2cm_with_mgii/4'>active site</scene> is located at one end of the beta-sheet sandwich containing two <scene name='32/32/Protein_pp2cm_with_mgii/6'>magnesium ions</scene> coordenated by <scene name='32/32/Protein_pp2cm_with_mgii/5'>Asp-109, Asp-208, Asp-298, and Asp-337</scene> residues.
| + | </td></tr><tr><td> |
| - | At high levels of branched-chain ketoacids PP2Cm dephosphorylates Ser-337 and activates mitochondrial BCKDC complex by associating with the E2 component of the complex.
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| - | The water molecules at the binuclear metal centre coordinate the phosphate group of the substrate, each ion is hexa-coordinated by <scene name='32/32/Protein_pp2cm_with_mgii/8'>oxygen atoms</scene> from water, providing a nucleophile and general acid in the dephosphorylation reaction, and Arg33 creates a local positive electrostatic potential on the protein for recognition of the phosphate group of the substrate. The nucleophile is the metal-bridging water molecule which could attack the phosphorus atom in an S<sub>N</sub>2 mechanism. Coordination to two Mg<sup>2+</sup> ions may stabilize the morenucleophilic hydroxide ion species. Other ions such as Ca<sup>2+</sup>, Zn<sup>2+</sup> and Ni<sup>2+</sup> inactivate the enzyme by competitively inhibiting Mn<sup>2+</sup> or Mg<sup>2+</sup> binding.
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| - | == branched-chain α-ketoacid dehydrogenase complex == | + | <span style="font-size:120%"> |
| | + | Soon Goo Lee, Hari B.Krishnan and Joseph M.Jez |
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| - | The human branched-chain α-ketoacid dehydrogenase (BCKD) complex is part of the mitochondrial α-ketoacid dehydrogenase complex family. Their structure consists of numerous copies of three enzymes E1, E2 and E3. A <scene name='32/32/E2b/1'> dihydrolipoyl transacylase (E2)</scene> forms the core
| + | PNAS, April 29, 2014, Vol. 111, No.17[https://doi.org/10.1073/pnas.1402243111] |
| - | of the complex with 24 copies in octahedral symmetry. Copies of the <scene name='32/32/E1/1'> α-ketoacid dehydrogenase (E1)</scene>, and copies of the<scene name='32/32/E3/2'> dihydrolipoamide dehydrogenase (E3)</scene>. In some types of (BCKDC) that are two regulatory enzymes proteins <scene name='32/32/Kinase/1'> protein kinase</scene> and <scene name='32/32/Phosphatase/1'> protein phosphatase</scene> that are attached to the E2 core through non-covalent bonds.
| + | </span> |
| | + | </td></tr></table> |
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| - | ==References, for further information on PP2Cm== | + | ==Structure Tour== |
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| - | * Ævarsson, A. ''et all'' "Crystal structure of human branched-chain α-ketoacid dehydrogenase and the molecular basis of multienzyme complex deficiency in maple syrup urine disease", CellPress. [https://www.sciencedirect.com/science/article/pii/S0969212600001052].
| + | <StructureSection load='4omz' size='350' side='right' caption='Crystal Structure of NolR from Sinorhizobium fredii (PDB entry [[4omz]])' scene=''> |
| - | * Wynn, R. M. ''et all'' "Structure, function and assembly of mammalian branched-chain α-ketoacid dehydrogenase complex", Alpha-Keto Acid Dehydrogenase Complexes. [https://link.springer.com/chapter/10.1007/978-3-0348-8981-0_7]
| + | ==Structural and Biological Significance== |
| - | * Lu, G. ''et all'' "Protein phosphatase 2Cm is a critical regulator of branched-chain amino acid catabolism in mice and cultured cells", The Journal of clinical investigation 119(6):1678-87. [https://www.researchgate.net/publication/24398300_Protein_phosphatase_2Cm_is_a_critical_regulator_of_branched-chain_amino_acid_catabolism_in_mice_and_cultured_cells].
| + | ===Global Regulation of Nitrogen Fixation Symbiosis=== |
| - | * Pan, B. F ''et all'' "Regulation of PP2Cm expression by miRNA-204/211 and miRNA-22 in mouse and human cells [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4816230/]
| + | NolR is a transcriptional regulator that fine-tunes the expression of nodulation (nod) and symbiosis genes across diverse Rhizobium species. Despite its critical ecological importance, the molecular basis of NolR's regulatory mechanism remained largely unknown until the comprehensive structural characterization presented in this paper. |
| | + | === Structural Architecture and DNA-Binding Mechanism=== |
| | + | The crystallographic structures of NolR reveal a homodimeric winged '''helix-turn-helix''' transcription factor, comprising two α-helical regions ('''α1 and α5''') forming the dimerization interface and a triangular configuration of helices ('''α2–α4''') that positions the conserved helix-turn-helix motif ('''α3–α4''') for DNA major groove binding. Notably, a distinctive "wing" composed of antiparallel β-sheets extends into the DNA minor groove. This architectural arrangement enables NolR to recognize '''asymmetric operator sequences'''—a remarkable feature that confers specificity and versatility in binding diverse target genes. |
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| | + | </StructureSection> |
