Online

Guth, Ethan C.

Biochemistry

2008

PhD

The aminoacyl-tRNA synthetases (aaRSs) are the universal set of enzymes responsible for attaching amino acids to tRNA to be used as substrates in the process of protein translation. As these enzymes act at the transition between nucleic acids and proteins, their specificity of action is critical for maintaining the fidelity of the genetic code. From a mechanistic standpoint, aaRS specificity is enforced by a complex series of tRNA structural and chemical elements that collectively make up its identity set and serve to distinguish one tRNA from another. Based on sequence, structure, and oligomeric differences, the aaRS family has been partitioned into two classes, each of which is responsible for roughly half of the 22 genetically encoded amino acids.
In the studies presented here, pre-steady-state kinetic methods were employed to measure individual events that collectively make up the catalytic cycle of the class I1 Escherichia coli Histidyl-tRNA Synthetase (HisRS) in order to elucidate the nature of its enzymatic activity and determine how these events contribute to the exquisite specificity between enzyme and tRNA. The results presented here indicate indentiy elements of tRNA[superscript His] regulate the activity of the amino acid activation and aminoacyl transfer half reactions. Additional evidence suggests communication between active sites of the HisRS homodimer plays a role in establishing an alternating cycle of catalysis in the steady state.