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{{Sandbox_ESBS}}<!-- PLEASE ADD YOUR CONTENT BELOW HERE --> | {{Sandbox_ESBS}}<!-- PLEASE ADD YOUR CONTENT BELOW HERE --> | ||
==Structure of the Mouse RNase H2 Complex== | ==Structure of the Mouse RNase H2 Complex== | ||
<StructureSection load='3kio' size='400' side='right' caption='mouse RNase H2 complex, (PDB code [[3kio]])> | <StructureSection load='3kio' size='400' side='right' caption='mouse RNase H2 complex, (PDB code [[3kio]])> | ||
'''The RNase H2 ribonuclease complex''' is a heterotrimeric endoribonuclease responsible for the major ribonuclease H activity in mammalian cells. In mouse, the complex is encoded by 3 genes located on chromosomes 8 (''Rnaseh2a''), 14 (''Rnaseh2b'') and 19 (''Rnaseh2c'')<ref> http://genome-euro.ucsc.edu/cgi-bin/hgTracks?clade=mammal&org=Mouse&db=mm10&position=RnaseH2&hgt.positionInput=RnaseH2&hgt.suggestTrack=knownGene&Submit=submit&hgsid=201143152_yP1Xd4bMnHS7DV0d3VcqpDSxzzuQ&pix=1563</ref>. This enzyme specifically cleaves the 3’O-Phosphate bond of RNA in a DNA/RNA hybrids to produce 5’ phosphate and 3’hydroxyl ends. | '''The RNase H2 ribonuclease complex''' is a heterotrimeric endoribonuclease responsible for the major ribonuclease H activity in mammalian cells. In mouse, the complex is encoded by 3 genes located on chromosomes 8 (''Rnaseh2a''), 14 (''Rnaseh2b'') and 19 (''Rnaseh2c'')<ref> http://genome-euro.ucsc.edu/cgi-bin/hgTracks?clade=mammal&org=Mouse&db=mm10&position=RnaseH2&hgt.positionInput=RnaseH2&hgt.suggestTrack=knownGene&Submit=submit&hgsid=201143152_yP1Xd4bMnHS7DV0d3VcqpDSxzzuQ&pix=1563</ref>. This enzyme specifically cleaves the 3’O-Phosphate bond of RNA in a DNA/RNA hybrids to produce 5’ phosphate and 3’hydroxyl ends. | ||
== Biological role == | == Biological role == | ||
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The first domain structure of the complex, H2A, contains 301 amino acids, almost as H2B protein which computes 308 amino acids. H2C protein is the smallest subunit: it only has 166 amino acids. | The first domain structure of the complex, H2A, contains 301 amino acids, almost as H2B protein which computes 308 amino acids. H2C protein is the smallest subunit: it only has 166 amino acids. | ||
Each of these proteins adopts various secondary structures with β-strands and α-helices: | Each of these proteins adopts various secondary structures with β-strands and α-helices: | ||
H2A protein has 12 α-helices, 11 β-strands and 3 turns<ref> http://www.uniprot.org/uniprot/Q9CWY8</ref>, | *H2A protein has 12 α-helices, 11 β-strands and 3 turns<ref> http://www.uniprot.org/uniprot/Q9CWY8</ref>, | ||
H2B molecule computes 8 α-helices, 7 β-strands and 3 turns<ref> http://www.uniprot.org/uniprot/Q80ZV0</ref>, | *H2B molecule computes 8 α-helices, 7 β-strands and 3 turns<ref> http://www.uniprot.org/uniprot/Q80ZV0</ref>, | ||
H2C subunit consists of 5 α-helices, 8 β-strands and 2 turns<ref> http://www.uniprot.org/uniprot/Q9CQ18</ref>. | *H2C subunit consists of 5 α-helices, 8 β-strands and 2 turns<ref> http://www.uniprot.org/uniprot/Q9CQ18</ref>. | ||
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H2C protein is found in the middle of the elongated complex structure, flanked by H2A and H2B proteins on the ends. | H2C protein is found in the middle of the elongated complex structure, flanked by H2A and H2B proteins on the ends. | ||
The complex is stabilized by the intimately interwoven architecture of H2B and H2C: The N-terminal region of H2B protein (amino acids 1-92) weaves together with H2C domain to form 3 β-barrels, also called “triple barrel”<ref name ="ref9"> Nicholson, Allen W. Ribonucleases. Springer Science & Business Media, 2011.</ref>. This triple barrel is formed from a total of 18 β-sheets and produces a pseudo-2-fold axis of symmetry along the central barrel. Also, it permits to leave the mostly α-helical C-terminal region of H2B available for potential interactions with other protein (for example the PCNA protein). Finally, it has been found that the motif provides a platform for securely binding the H2A protein: the side and end of the first barrel in the subcomplex H2B/H2C form a <scene name='60/604486/Tight_interface_h2ah2c/2'>tight interface</scene> with amino acids 197-258 in the C-terminal region of H2A protein. This interface is composed mainly of hydrophobic residues<ref name="ref5">. | The complex is stabilized by the intimately interwoven architecture of H2B and H2C: The N-terminal region of H2B protein (amino acids 1-92) weaves together with H2C domain to form 3 β-barrels, also called “triple barrel”<ref name ="ref9"> Nicholson, Allen W. Ribonucleases. Springer Science & Business Media, 2011.</ref>. This triple barrel is formed from a total of 18 β-sheets and produces a pseudo-2-fold axis of symmetry along the central barrel. Also, it permits to leave the mostly α-helical C-terminal region of H2B available for potential interactions with other protein (for example the PCNA protein). Finally, it has been found that the motif provides a platform for securely binding the H2A protein: the side and end of the first barrel in the subcomplex H2B/H2C form a <scene name='60/604486/Tight_interface_h2ah2c/2'>tight interface</scene> with amino acids 197-258 in the C-terminal region of H2A protein. This interface is composed mainly of hydrophobic residues <ref name="ref5">. | ||
== Interactions with nucleic acids == | === Interactions with nucleic acids === | ||
It has been proved that the position of RNA/DNA complex in the active site cleft is determined by several favorable electrostatic interactions between the nucleic acid and positively charged amino acids of the protein<ref name = "ref2">. | It has been proved that the position of RNA/DNA complex in the active site cleft is determined by several favorable electrostatic interactions between the nucleic acid and positively charged amino acids of the protein<ref name = "ref2">. | ||
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== Activity == | === Activity === | ||
The RNase H2 recognize 2’OH group of ribonucleotides in RNA at RNA/DNA junction and cannot cleave unhybridized RNA. The phosphodiester hydrolysis catalysed by the RNase H2 is likely following a two-metal ion-dependent mechanism quite common for phosphoryl hydrolases like RNase H enzymes. | The RNase H2 recognize 2’OH group of ribonucleotides in RNA at RNA/DNA junction and cannot cleave unhybridized RNA. The phosphodiester hydrolysis catalysed by the RNase H2 is likely following a two-metal ion-dependent mechanism quite common for phosphoryl hydrolases like RNase H enzymes. | ||
