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Hou Research

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Professor

233 South 10th Street
BLSB 220
Philadelphia, PA 19107

215-503-4480

The tRNA molecules are essential for the specificity of decoding, which is the key determinant in the speed and quality of cell growth. Elevated levels of tRNAs can lead to cancer, while deficiency in tRNAs can lead to cell toxicity.

Our research provides the basis to gain biochemical, structural, and bioinformatic insights into tRNAs in evolution. These insights are important for understanding the origins of the genetic code and for developing new strategies for drug targeting against diseases arising from errors of tRNA functions.

We have developed a variety of methods, including biochemical, structural, kinetic, and genetic approaches. We focus on one representative enzyme in each case and build a framework of information by examining the enzyme in the larger biological context. Because tRNAs are ancient and enzymes that interact and recognize tRNAs are also ancient, we have a large database to search for related and homologous enzymes in evolution. The tRNA-interacting network is broad and include enzymes and proteins that are in pathways unrelated to protein synthesis. Some of our work published in various journals is mentioned in our publications page.

Research Projects

How does tRNA methylation regulate gene expression?

Methylation of tRNA is the most common form of post-transcriptional modification. With the addition of just one methyl group to a nucleobase or a backbone group, tRNA can gain structural stability in a particular region or decoding specificity upon pairing with an mRNA codon. However, how each methylation confers a unique strength to tRNA is poorly understood.

Recent advance in tRNA biology has opened a new era, in which the primary challenge is no longer to simply know what methylation is expressed and where, but rather to determine how each methylation impacts translation of codons and expression of genomes. We have focused on the m1G37-tRNA methylation, which is necessary to maintain protein synthesis reading frame. Loss of m1G37-tRNA leads to accumulation of +1 frameshift errors, resulting in pre-mature termination of translation and cell death. We are interested in the biology of this methylation and how it regulates gene expression.

How is a tRNA specifically methylated?

The active site of TrmD, the bacteria-specific m1G37-tRNA methyl transferase, uses a knotted protein fold to catalyze methyl transfer. Christian et al., NSMB (2016). The specificity of anticodon-codon base pairing cannot be achieved simply by 3 base pairs. Methylation and modifications of bases adjacent to the anticodon-codon region are necessary.

The m1G37-tRNA methylation is essential for bacterial cell growth. The TrmD enzyme that synthesizes the methylation is unrelated to its human counterpart Trm5, suggesting that TrmD is an attractive target for high throughput screening of novel antibiotics. Other methylation and modifications are essential to protect against oxidative damage on tRNA.

How is a tRNA specifically charged with an amino acid?

While all tRNA molecules are similar in both the secondary and tertiary structure, how is each specifically charged with an amino acid?

How does impaired tRNA charging and aminoacylation cause human disease? Human Charcot-Marie-Tooth disease is an example where mutations in charging enzymes cause peripheral neuropathy. Other examples involving mutations in tRNA charging enzymes include epileptic encephalopathy. What is the molecular basis that links impaired tRNA charging to these disease phenotypes?

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