Centre for Cellular & Molecular Biology, Hyderabad

SEMINAR

Chiral Proofreading During Translation of the Genetic Code

Abstract
Editing or proofreading domains of aminoacyl-tRNA synthetases (AaRSs) hydrolyze misaminoacylated-tRNAs thereby maintaining a high fidelity during translation. Archaeal threonyl-tRNA synthetases (ThrRSs) possess an editing domain that is unrelated to its bacterial/eukaryotic counterparts. The domain bears a striking structural homology to D-aminoacyl-tRNA deacylases (DTDs), which remove D-amino acids charged on tRNA. We earlier suggested that the ThrRS editing domain from Pyrococcus abyssi (Pab-NTD) does not use any specific side chains for catalysis but employs a RNA-assisted water mediated catalytic mechanism. Our recent findings with three distinct archaea have shown that the domain does not use specific side chains not only for catalysis but also for substrate specificity (1). We have also elucidated a crucial 'chiral proofreading' mechanism by which D-amino acids are prevented by DTD from infiltrating the translational machinery (2). Further work on DTD suggests a mechanistic design problem that might lead to cross-reaction with a couple of other aminoacyl-tRNAs in the cell. The striking functional consequences of the above misacylation reactions will be presented.

References:
1) Ahmad et al. Nature Communications (2015) 6,7552, 1-12.
2) Ahmad et al. eLife (2013) 2, e0159, 1-18.

BIOGRAPHY

2002-present: Scientist at CCMB, Hyderabad.
1986-2002: Post-doctoral associate at IGBMC, Strasbourg, France.
1996: PhD, Indian Institute of Science, Bangalore.

Research Fields and Interests:
A major focus of Dr. Rajan Sankaranarayanan’s laboratory is on understanding how a high accuracy is achieved using editing/proofreading mechanisms during translation of the genetic code. His laboratory has contributed significantly to our understanding of chirality based proofreading mechanisms and their functional implications. In addition, his laboratory has shown the structural and functional basis of several enzymes from Mycobacterium tuberculosis involved in complex lipid synthesis.

Selected Publications:

Ahmad, S., Muthukumar, S., Kuncha, S. K., Routh, S. B., Yerabham, A. S. K., Hussain, T., Kamarthapu, V., Kruparani, S. P. and Sankaranarayanan, R. (2015) Specificity and catalysis hardwired at the RNA-protein interface in a translational proofreading enzyme. Nature Commun. 6:7552 doi: 10.1038/ncomms8552.

Ahmad, S., Routh, S. B., Kamarthapu, V., Chalissery, J., Muthukumar, S., Hussain, T., Kruparani, S. P., Deshmukh, M. V. and Sankaranarayanan, R. (2013) Mechanism of chiral proofreading during translation of the genetic code. eLife 2, e01519. (#Highlighted as Science Editor's Choice article: 'Chirality Check' Science Vol. 343, p119; 10th January, 2014)

Chhabra, A., Haque, A. S., Pal, R. K., Goyal, A., Rai, R., Joshi, S., Panjikar, S., Pasha, S., Sankaranarayanan, R.* and Gokhale, R. S.* (2012) Nonprocessive [2+2]e- off-loading reductase domains from mycobacterial nonribosomal peptide synthetases. Proc. Natl. Acad. Sci. (USA) 109, 5681-5686.

Hussain, T., Kamarthapu, V., Kruparani, S. P., Deshmukh, M. V. and Sankaranarayanan, R. (2010) Mechanistic insights into cognate substrate discrimination during proofreading in translation. Proc. Natl. Acad. Sci. (USA)107, 22117-22121. (#Covered by an accompanying Commentary article in the same PNAS issue titled 'Proofreading in translation: Dynamics of the double-sieve model' p21949-50)

Arora, P., Goyal, A., Natarajan, V. T., Rajakumara, E., Verma, P., Gupta, R., Yousuf, M., Trivedi, O. A., Mohanty, D., Tyagi, A., Sankaranarayanan, R.* and Gokhale, R. S.* (2009) Mechanistic and functional insights into fatty acid activation in Mycobacterium tuberculosis. Nature Chem. Biol. 5, 166-173.