David L. Thurlow
Biochemistry, Molecular Biology
Office S229, Sackler Sciences Center
Postdoctoral Fellow, Strasbourg, France
Ph.D. University of Massachusetts
B.A. Bowdoin College
Director of Medical Careers Advising Program
As Director of Clark’s Medical Careers Advising Program and Chair of the Premedical and Predental Advisory Committee, Dr. Thurlow advises students interested in health related professions including medical doctors (MD, DO), dentistry, optometry, podiatry, veterinary medicine, physician assistant, nurse practioner, physical therapy, occupational therapy, public health, and many others. Many new features of our program help students find their own “right path” into medicine and assist the Premedical and Predental Advisory Committee in preparing personalized letters of recommendation for Clark students applying to medical and dental schools.
Adding "CCA" to tRNAs
For nearly 20 years, our group investigated the molecular basis underlying interactions between transfer RNA (tRNA) and the processing enzyme ATP,CTP:tRNA nucleotidyltransferase ("NT"). NT catalyzes joining of CMP and AMP onto the 3'end of tRNA molecules that lack all or part of the universally conserved sequence CCA. We are trying to understand how this enzyme adds only the CCA sequence without using a nucleic acid template.
- Chemical modification experiments identified bases essential for interaction with NT that are located at the “corner” of a tRNA’s three dimensional structure, where the T- and D-loops come together. These results suggested a model in which NT interacts along the “top” of a tRNA, with one end binding to the tRNA’s corner and the other end binding the nucleotide substrates and adding them to the 3’end of the tRNA.
- Mini RNA helices, structural analogs of the “top” of a tRNA, were shown to be effective substrates for NT – thereby confirming our model for the interaction based on chemical modification experiments.
- Site-directed mutagenesis of NT genes created enzymes with altered amino acid sequences, or large deletions. The mutants, as anticipated, exhibited decreased enzymatic activity – some because they reduced the ability of the tRNA to bind and some because they reduced binding of the nucleotides.
- Computer modeling of interactions between NT and its substrates ATP, CTP, and tRNA revealed possible differences among the many ways in which ATP and CTP could bind.
Hypothetical model for NT interacting with the top of a tRNA (left), based on chemical modification experiments - sketched by Fred LaRivere’94, while working in our lab as an undergraduate in 1993, compared to crystal structure (right) published over ten years later (Xiong and Steitz (2004), Nature 430:640):
Computer-based predicted model for the catalytic region of a Class I NT constructed by our group (Megan Albert '02) in collaboration with a lab in Poland (Janusz Bujnicki) (left), just prior to the publishing of the first crystal structure of a Class I NT (right; by Okabe et al. (2003) EMBO J. 22:5918-5927).
Bujnicki J.M., *Albert M.A., Nelson D.J., Thurlow D.L. (2003). “Fold recognition, homology modeling, docking simulations, kinetics analysis and mutagenesis of ATP/CTP:tRNA nucleotidyltransferase from Methanococcus jannaschii."Proteins: Structure, Function and Genetics, 52(3): 349-59.
M. Seth, D.L. Thurlow and Hou, Y.M. (2002). "Poly(C) Synthesis by Class I and Class II CCA-Adding Enzymes." Biochemistry, 41: 4521-32.
A.S. Reichert, D.L. Thurlow, and M. Mörl (2001). "A eubacterial origin for thehuman tRNA nucleotidyltransferase?" J. Biol. Chem, 382: 1431-1438.
D.L. Thurlow, G.M. *Pulido and K.J. *Millar (1997). "Unidentified open reading frames in the genome of Methanococcus jannaschii are similar in sequence to an archaebacterial gene for tRNA nucleotidyltransferase." Journal of Molecular Evolution, 44: 686-689.
Z. Li, Y. Sun and D.L. Thurlow (1997). "RNA minihelices as model substrates for ATP/CTP:tRNA nucleotidyltransferase." Biochem. J., 327: 847-851.
Z. Li, K.A. Gillis, L.A. Hegg, J. Zhang and D.L. Thurlow (1996). "Effects of nucleotide substitutions within the T-loop of precursor tRNAs on interaction with ATP/CTP:tRNA nucleotidyltransferases from Escherichia coli and yeast." Biochem J., 314: 49-53.