Department of Biochemistry

Tijana Ivanovic

Assistant Professor of Biochemistry

 

Research Description

Uncovering fundamental molecular mechanisms of virus translocation across biological membranes

Research in the Ivanovic Laboratory focuses on uncovering fundamental molecular mechanisms of virus translocation across biological membranes, in the distinct contexts of enveloped-virus membrane fusion and nonenveloped-virus membrane penetration. We apply and develop advanced biophysical and biochemical approaches and combine them with those of virology, molecular biology and cell biology.

Membrane fusion is at the heart of many essential biological processes, including intracellular transport, neurotransmission, gamete union, and cell entry by enveloped viruses. At least the main features of the mechanism of fusion can be generalized to all membrane fusion systems. The apparent parallels between different systems help drive the research forward, as many mechanistic observations, as well as technologies or approaches to addressing them, can often be extended to related systems. Although our current molecular picture is incomplete for any membrane fusion mechanism, it is now possible to achieve complete understanding of viral membrane fusion through advanced microscopy techniques that allow the study of biological processes at the single-molecule level.

Nonenveloped viruses are not enclosed in a cell-derived membrane bilayer, and, thus, cannot enter cells with benefit of membrane fusion. They serve as an extreme example of direct (not fusion assisted) macromolecular translocation because of the requirement to transport exceptionally large cargos to the target cell during initiation of infection. These cargos consist of viral genome-nucleoprotein complexes that may even include a protein coat (the viral capsid). Mechanisms of nonenveloped virus membrane penetration remain poorly understood because of the current inability to reconstitute this process in vitro.

Single-molecule approaches are enabling direct studies of molecular mechanisms by allowing measurements of individual molecular “trajectories” within a population. They obviate the need for synchronization and indirect inferences inherent in ensemble-averaged approaches. We build custom laser microscopes and apply Total Internal Reflection Fluorescence (TIRF) microscopy to follow in real time hundreds of influenza virions undergoing various molecular transitions that precede productive cell entry. Statistical analyses of individual-virion data – combined with structure-based mutagenesis and computer simulations that verify experimentally derived models – have led to a detailed molecular description capturing the sequence of events at the virus-target membrane interface that induce fusion of the participating membranes. By answering questions about what is fundamental about the viral fusion mechanism and what available options a virus has to change, it is becoming possible to think a step ahead of the virus to devise novel treatment approaches. The newly enabled level of mechanistic appreciation is further likely to be vital in aiding universal vaccine development and efforts seeking to understand the barriers to cross-species transmission and adaptation. Our laboratory further works on developing a novel set of methodologies that will recapitulate in vitro the entire process of membrane penetration by nonenveloped viruses, as well as enable the studies of this process at the single-virion level.

Our research aims to bring this new, multidisciplinary technology and approach in the study of biological systems to address some of the challenging questions both about the general character of virus systems, and to bring about discoveries and advances in understanding of important human pathogens.