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Histidyl-tRNA Synthetase

Histidyl tRNA Synthetase (HisRS) is a 94kD 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^[1]. Class I and Class II differ mainly with respect to the topology of the catalytic fold and site of esterification on cognate tRNA^[1]. Class II enzymes have a 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, comprising the tetrameric PheRS and GlyRS class II synthetases>PMID: 1852601</ref>.

spinqualitylabelsall models Structure of Histidyl-tRNA Synthetase (PDB entry 1KMM) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image 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[2]. 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[2].

Mechanism

tRNA

3D Structures of Histidyl-tRNA Synthetase

1KMN

1KMM

1HTT

2EL9

References

1. ↑ ^{1.0 1.1} Eriani G, Delarue M, Poch O, Gangloff J, Moras D. Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs. Nature. 1990 Sep 13;347(6289):203-6. PMID:2203971 doi:http://dx.doi.org/10.1038/347203a0
2. ↑ ^{2.0 2.1} Francklyn, C., and Arnez, J.G. (2004) in Aminoacyl-tRNA Synthetases (Ibba, M.,Francklyn, C.,Cusack, S.. Eds.) Landes Publishing, Austin, TX