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 <scene name='User:Jamie_Abbott/Sandbox2/Hisa_loop/1'>HisA Loop</scene> ) 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 <scene name='User:Jamie_Abbott/Sandbox2/Motif_iii/4'>motif III</scene>) comprises the histidine binding pocket floor and wall. Finally, conserved side chains that make direct contact with histidine are Glu83 and Gly127 (<scene name='User:Jamie_Abbott/Sandbox2/Motif_ii/2'>motif II</scene>), 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>

----

----

== Mechanism ==

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

----

== 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]

----

== References ==

<references/>