Ya-Ming Hou, PhD

Mechanisms of tRNA functions and protein synthesis by the ribosome

Functions of tRNA in protein synthesis. My research focuses on understanding the structure-function activities of tRNAs, which are the L-shaped adaptors between mRNA and protein sequences during genetic decoding. During decoding, a tRNA is charged with a specific amino acid to form an aminoacyl-tRNA, which enters the ribosome at a codon position cognate to the anticodon. In the ribosome, the charged tRNA donates its amino acid to peptide bond formation and then transits through. The entire process is complex, dynamics, and includes different tRNA activities and functions that are achieved by interactions with various protein partners.

Perturbation of protein synthesis leads to neurodegenerate diseases. In neurons, the protein synthesis machinery can occur near the cell body or in distal and local neuronal processes. The local protein synthesis has been implicated in many aspects of neuronal development and functions, such as axon guidance, dendritic elaboration, synaptic plasticity, and long-term memory formation. Dysfunction of protein synthesis has been implicated in human neurological disorders, such as fragile X syndrome, Charcot-Marie-Tooth disease, spinal muscular atrophy, and various mitochondrial dysfunctions.

What determines successful protein synthesis? The key determinant for successful protein synthesis is a delicate balance between speed (~10 amino acids per sec) and specificity (at an error rate of 10-4). To ensure this balance, we are studying four key steps. The first is aminoacylation of tRNA catalyzed by aminoacyl-tRNA synthetases. Mutations in the aminoacylation reaction can lead to protein misfolding and neuro-degeneration as manifested in the Charcot-Marie-Tooth neuropathy. Second, we are studying the m1G37 methyl transferase, which uses the methyl group of S-adenosyl methionine to form the m1G37 modification adjacent to the anticodon of a subset of tRNAs, which is essential for the decoding specificity. Mutations that perturb this modification lead to cell death. Third, we are studying the tRNA 3' end maturation reaction, catalyzed by the CCA-adding enzyme, which renders tRNA eligible for protein synthesis. We have shown that this CCA maturation provides a kinetic quality control that rejects damaged tRNA from protein synthesis. Fourth, we are investigating how tRNA-ribosome communicates during translocation to understand the basis of specificity.

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