Abstracts
By Prof Susan A. Martinis:
A new class of antimicrobial boron-containing compounds called the oxaboroles was discovered as a potent inhibitor of an enzyme called leucyl-tRNA synthetase (LeuRS) that is essential to setting the genetic code for protein synthesis in all living organisms. Kerydin has just been marketed by Anacor Pharmaceuticals, start-up biotechnology company, to treat fungal infections of the toenail. Significantly, its novel mechanism of action has been capitalized upon broadly by the pharmaceutical industry as a powerful lead to develop whole new families of drugs to treat spectra of bacterial, fungal, and parasitic infections, as well as other diseases. Kerydin inactivates LeuRS by effectively crosslinking its bound tRNA substrate to form a tight protein:RNA:small molecule complex that can not turnover to reactivate. Resistance mutations to Kerydin or its derivatives have been localized in a secondary editing site of LeuRS that is designed to clear mistakes that would undermine the genetic code. These resistance mutations provide a unique opportunity to define drug mechanisms, as well as critical mechanisms to maintain quality control for protein synthesis. Investigation of these resistance sites has uncovered a tyrosine amino acid three-state “switch” that is important to editing, as well as a peptide “lid” that sequesters the editing site in fungal LeuRS. The drug’s mechanism of action relies upon a specific conformation of one of these fungal LeuRS states. Mechanistic distinctions of fungal and bacterial LeuRSs could also be capitalized upon for development of the oxaborole family as a broad spectrum antibiotic.
By Prof Karin Musier-Forsyth:
All retroviruses use specific host cell tRNAs to prime reverse transcription of their retroviral RNA genomes into DNA. The primer for reverse transcription in HIV-1, human tRNALys, is selectively incorporated into virions during viral assembly. Surprisingly, the speaker finds that a specific tRNALys binding protein, human lysyl-tRNA synthetase (LysRS), is also specifically packaged into HIV-1 leading to the enrichment of tRNALys in virions. A highly conserved region of the HIV-1 RNA genome is responsible for regulating many steps of the retroviral lifecycle. The speaker shows that part of this region mimics the L-shaped fold of tRNA, providing a structural basis for understanding how this genomic RNA coordinates interactions with a tRNA-binding host factor to facilitate initiation of reverse transcription. Cytoplasmic LysRS is normally localized to a dynamic mammalian multisynthetase complex (MSC). In addition to their normal function in translation, many tRNA synthetases have been shown to be mobilized from the MSC and to function in a wide variety of non-translational pathways including inflammation, immune activation, and metastasis. Using immunofluorescence and confocal microscopy the speaker finds that LysRS localization is dramatically altered upon HIV-1 infection. In uninfected cells, the majority of LysRS is in the MSC, as expected, whereas LysRS is released from the MSC and traffics to the nucleus following HIV-1 infection. These findings have implications for the potential development of novel anti-retroviral therapies.
About the speakers
Prof Susan A. Martinis earned her PhD at the University of Illinois in 1990, and then trained at the Massachusetts Institute of Technology as an American Cancer Society Postdoctoral Fellow. She was hired in 1993 at a start-up biotechnology company Cubist Pharmaceuticals as its third employee, before moving to academia at the University of Houston in 1997. Cubist Pharmaceuticals grew to over 600 people, developed the life-saving drug Cubicin, and was recently acquired by Merck Pharmaceuticals. Professor Martinis received tenure in University of Houston where she received the University’s Enron Teaching Excellence Award, College Teaching Excellence Award, and Houston Alumni Organization Outstanding Faculty Award. She moved to the University of Illinois in 2005, where she is currently a University Scholar and has held the position of Head of the Department of Biochemistry for 5 years. Her research program on the aminoacyl-tRNA synthetases is currently supported by the National Institutes of Health, National Science Foundation, and W.M. Keck Foundation.
Prof Karin Musier-Forsyth obtained her PhD in Chemistry from Cornell University in 1989. She was an American Cancer Society Postdoctoral Fellow in the laboratory of Prof Paul Schimmel at Massachusetts Institute of Technology from 1989-92. She joined the faculty at the University of Minnesota in 1992, where she served on the faculty for 14 years. She was named Merck Professor of Chemistry in 2003 and Distinguished McKnight University Professor in 2006. In 2007, she moved to her current position at the Ohio State University, where she is the Ohio Eminent Scholar in Biological Macromolecular Structure and Professor of Chemistry and Biochemistry. Prof Musier-Forsyth’s research group currently uses a wide variety of chemical and biophysical approaches to answer fundamental questions focusing on nucleic acids (RNA and DNA) and proteins that are involved in translation of the genetic code and viral replication.
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