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Department of Chemistry Seminar
April 22, 2019 @ 4:10 pm - 5:00 pm
Dr. Martin Lawrence, Professor of Biochemistry, Structural Biology, Virology, CRISPER/Cas at Montana State University
Hosted by ChulHee Kang
Easy Peasy, Lemon Squeezy; A New Structural Paradigm for Viral Assembyans Genone Delivery
Archaea constitute more than 20% of the biomass on earth and viruses infecting Archaea make significant contributions to global biogeochemical cycles. For example, virus-induced lysis of archaea in sea floor sediments accounts for up to one-third of the total microbial biomass killed, resulting in the release of ~0.3 to 0.5 gigatons of carbon per year globally. Many archaeal viruses are constructed of lemon-shaped heads with long tubular tails extending from one or both ends. This morphology is not seen in eukaryotic viruses or bacteriophage. Until now, however, structural heterogeneity intrinsic to these viruses has hindered efforts to elucidate their molecular architecture. We have utilized a combination of cryo-electron microscopy and X-ray crystallography to study Acidianus tailed spindle virus (ATSV). Cryo-electron tomography shows a smooth transition from the lemon-shaped head into the tubular-shaped tail, and allows low resolution structural modeling of individual virions. Remarkably, higher dose 2D micrographs reveal a helical surface lattice in the lemon-shaped head. Consistent with this, crystallographic studies of the major capsid protein reveal a decorated four-helix bundle that packs within the crystal to form a four-start super-helical assembly with structural similarity to the tube-shaped tail. Combined, this suggests that the lemon-shaped capsid is formed by a multi-start helical assembly with a smoothly varying radius and allows construction of a pseudo-atomic model for the lemon-shaped capsid that extends into a tubular tail. The potential advantages that this novel architecture conveys to the evolution and life cycle of spindle-shaped viruses, including a role in DNA ejection, will be discussed.