User:Jamie Abbott/Sandbox2

== Histidyl-tRNA Synthetase ==

Histidyl tRNA Synthetase (HisRS) is a 94kD <scene name='User:Jamie_Abbott/Sandbox2/Hisrsdimer/2'>homodimer</scene> that belongs to the Class II of aminoacyl-tRNA synthetases (aaRS). Aminoacyl-tRNA synthetases have been partitioned into two classes, containing 10 members, on the basis of sequence comparisons<ref name="Eriani">PMID: 2203971</ref>. Class I and Class II differ mainly with respect to the topology of the catalytic fold and site of esterification on cognate tRNA<ref name="Eriani" />. Class II enzymes have a <scene name='User:Jamie_Abbott/Sandbox2/Catalytic_domain/1'>catalytic domain</scene> composed of anti-parallel β-sheets and α-helices (residues 1-325). Additionally, class II enzymes can be further divided into three subgroups: class IIa, distinguished by an N-terminal catalytic domain and C-terminal accessory domain (later shown to be anticodon binding domain); class IIb, whose anticodon binding domain is located on the N-terminal side of the fold; and class IIc, encompassing the tetrameric PheRS and GlyRS class II synthetases.<ref name="Cusack91">PMID: 1852601</ref>

'''Function and Catalysis'''<StructureSection load='1KMM' size='500' side='right' caption='Structure of Histidyl-tRNA Synthetase (PDB entry [[1KMM]])' scene=''>Class II aminoacyl-tRNA synthetases aminoacylate the 3'OH of their cognate tRNAs.

The active site to HisRS contains a histidine binding pocket composed of highly conserved residues found in distinct sequences motifs. First, the LV/AAGGGLDYY loop (or HisA loop) forms one wall of the binding pocket. This HisA loop is highly conserved and extends over a part of the active site<ref name="aaRSbk">Francklyn, C., and Arnez, J.G. (2004) in ''Aminoacyl-tRNA Synthetases'' (Ibba, M.,Francklyn, C.,Cusack, S.. Eds.) [http://www.landesbioscience.com/books/iu/id/810/?nocache=145477703 Landes Publishing, Austin, TX]</ref>. Second, the glycine-rich β-strand (sequence AGGRYDGL preceding motif III) comprises the histidine binding pocket floor and wall. Finally, conserved side chains that make direct contact with histidine are Glu83 and Gly127 (motif II), which contact the α-amino and α-carbonyl functional groups, respectively, and Glu131 (motif II) and Tyr264, which make hydrogen bonds to the Nδ and Nε, respectively, of the imidazole ring<ref name="aaRSbk" />.</StructureSection>

<scene name='User:Jamie_Abbott/Sandbox2/Hisrsdimer_to_monomer/2'>Monomer</scene>

<scene name='User:Jamie_Abbott/Sandbox2/Motif_i/3'>Motif I</scene>

<scene name='User:Jamie_Abbott/Sandbox2/Motif_ii/2'>Motif II</scene>

<scene name='User:Jamie_Abbott/Sandbox2/Motif_iii/4'>Motif III</scene>

<scene name='User:Jamie_Abbott/Sandbox2/Hisa_loop/1'>HisA Loop</scene>

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== Mechanism ==

[http://proteopedia.org/wiki/index.php/TRNA tRNA]

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== Evolutionary Conservation ==

=== Structural Homology ===

== 3D Structures of Histidyl-tRNA Synthetase ==

[http://www.pdb.org/pdb/explore/explore.do?structureId=1KMN 1KMN]

[http://www.pdb.org/pdb/explore/explore.do?structureId=1KMM 1KMM]

[http://www.pdb.org/pdb/explore/explore.do?structureId=1HTT 1HTT]

[http://www.pdb.org/pdb/explore/explore.do?structureId=2EL9 2EL9]

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== References ==

<references/>