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Host entry mechanisms of Salmonella and Shigella phages

RIT College of Science
Event organized by RIT College of Science

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SPEAKER: Kristin N. Parent, Michigan State University

LOCATION: A300 Thomas Gosnell Hall
Reception to follow in the Bruce and Nora James Atrium

The molecular mechanisms that govern Podoviridae genome delivery are not completely understood. Productive infection requires precise docking to a designated location on the cell surface to enable delivery of the viral genome through several steps that may include: initial specific recognition of the cell surface through interaction with a host receptor, followed by coordinated conformational changes in viral proteins, and ultimately genome transfer into the target cell. Such transfer is a universal phenomenon among viruses and must be highly regulated since evolutionary pressures demand that errors leading to premature or inappropriate release be avoided.

Bacterial outer membrane proteins (Omp) A and C co-purify have been identified as important for Podoviridae entry into Salmonella and Shigella [1-4]. We performed a combination of in vivo studies with three omp null mutants of Shigella flexneri, including classic phage plaque assays and time-lapse fluorescence microscopy to monitor genome ejection at the single virion level [2]. We also performed cryo-electron tomography of phage “infecting” outer membrane vesicles and have shown the tail contacts and indents the outer membrane. Mutagenesis work has demonstrated key regions in Omp A that mediate infection [3]. Furthermore, experimental evolution studies have elucidated the proteins within Sf6 that likely interact with Omps A & C.

Furthermore, we isolated Shigella phages from environmental samples, and found they were highly abundant and easy to isolate from water samples. We found 18 novel phages, 16 of which infected various Shigella species. Some have the innate ability to utilize Omp A and/ or Omp C, indicating that the innate ability to utilize multiple receptors is a not only a trend in Shigella phages, but also extends to long-tailed phages as well.

Recently, we expanded our studies to include transposon and single gene deletion libraries to screen over 5,400 non-essential genes in Salmonella to identify additional gene products that play a role during phage infection. We identified over 200 gene products that either protect the host against the phage or facilitate phage entry. This study elucidated a novel inner membrane protein, YajC, that is critical for facilitating genome ejection across the inner membrane during Podoviridae infection.

Kristin Parent is a professor of biochemistry and molecular biology at Michigan State University. Her research focuses on underlying mechanisms that control virus infection, including the giant Samba virus from the Brazilian Amazon, and phages from the diarrhea causing Shigella flexneri.

Parent is also doing pioneering research to advance the use of electron cryo-microscopy (cryoEM) and three-dimensional image reconstruction methods when applied to large and challenging biological specimens that are currently outside cryoEM imaging limitations.

Her work includes combination of biochemistry, molecular biology, biophysics and structural biology. She has over 30 research papers and several of these have been featured in designs as journal covers. For example, she was first author on a 2010 paper that appeared in Structure that was highlighted on the journal cover.

Another one of her 2010 first author papers appeared in a special issue of Physical Biology and was also highlighted on the journal cover. Other notable cover designs include a 2012 Virology article on bacteriophage Sf6, a 2013 featured image in mBio on the structure of Trichomonas vaginalis virus, and a 2014 Virology cover on the bacteriophage CUS-3.

The most recent cover design published in 2017 features work from graduate student Jason Schrad on the characterization of the giant Samba virus in the journal Viruses.

Parent received her B.S. degree in Molecular and Cell Biology and her Ph.D. degree in Biochemistry from the University of Connecticut and served as a postdoctoral fellow at the University of California, San Diego.

Her doctoral studies were partially supported by National Institutes of Health (NIH) Predoctoral Fellowship Program and she also received an NIH Postdoctoral Fellowship. Her lab includes undergraduate and graduate students, postdoctoral fellows and visiting researchers.

Dr. Parent has brought and developed the revolutionary technique of cryo-electron microscopy (cryo-EM) to Michigan State University, and continues to be an emerging national leader in this field. When Parent was hired at MSU in 2013, she retrofitted an old microscope on campus to become cryo-capable, added a state-of-the-art direct detection device camera, and established a computational pipeline to allow cryo-EM studies to be conducted in-house.

These efforts earned her an award from AAAS for Women in the Chemical Sciences, and as part of this award Parent attended a leadership and professional development workshop in Washington DC. Parent also became part of an NIH-sponsored Midwest consortium to gain access to high-resolution cryo-EM facilities with Purdue University.

Lastly, she was the co-organizer of a 2016 symposium on cryo-EM at the Microscopy Society of America national conference. Parent continues to assume myriad leadership roles within the field of cryo-EM.