Kvansakul - Structural biology of cell death and host-pathogen interactions
All life is shaped by the constant struggle between hosts and microbial threats. The interface between host and pathogens represents a major frontier for biomedical and biotechnological applications. We aim to understand at the atomic level two such molecular battlefields. We hope to understand how viruses hijack cellular defence systems to ensure their own proliferation and survival. Our second major area of interest centers on the role of small proteins that act as a first line of defence against microbial targets such as fungi, and the mechanism that these molecules use to destroy target cell membranes.
Our primary tool to help us understand these processes is X-ray crystallography, a technique that is able to reveal in exquisite detail the molecular mechanisms operating at both these host-pathogen interfaces. We aim to use our insights to ultimately design new therapeutics against a range of diseases including microbial infections and cancer.
Viral subversion of host cell apoptosis
The programmed death of cells (apoptosis) is a critically important mechanism that enables multicellular organisms to eliminate damaged, infected or unwanted cells during development, growth and tissue homeostasis. Failure to regulate apoptosis leads to a number of diseases including arthritis, autoimmune diseases and cancer. Viruses have evolved a powerful ability to inhibit host cell apoptosis in response to viral invasion to ensure their own survival and proliferation.
We are interested in understanding the molecular mechanism underlying virus-mediated inhibition of apoptosis using X-ray crystallography, a technique that allows us to visualise the molecules responsible for apoptosis inhibition at the atomic level.
Tumour viruses: The ability of pathogenic viruses to disable the cell death machinery of invaded host cells is of critical importance for viral infectivity, persistence and replication. Viral infections, such as those by gamma-herpesviruses including Kaposi's sarcoma-associated herpesvirus (KSHV) or Epstein-Barr virus (EBV), have been shown to be intimately linked to malignancies including Kaposi's sarcoma or Burkitt's lymphoma. A key group of virulence factors that allows gamma herpesviruses to overcome the apoptotic machinery of host cells and persist in the host are viral Bcl-2 proteins.
We are currently investigating how viral Bcl-2 proteins contribute to the development and maintenance of virus-associated tumours such as Burkitt's lymphoma and Kaposi's sarcoma.
Poxviruses: Viruses have a powerful ability to inhibit host cell apoptosis in response to viral invasion. The importance of Bcl-2 proteins for controlling apoptosis is highlighted by the number of viruses that express identifiable homologs of Bcl-2. However, a number of poxviruses do not contain obvious Bcl-2 homologs, despite repressing host cell apoptosis after infection.
Using X-ray crystallography, we showed that the two poxviral proteins M11L (myxoma virus) and F1L (vaccinia virus) adopt a Bcl-2 fold, despite lacking sequence similarity to any other cell-death inhibitor. More importantly, they inhibit apoptosis using a mechanism similar to mammalian Bcl-2 proteins. This suggests that many other anti-apoptotic viral proteins exist that are not readily identifiable on a primary amino acid sequence level.
Structural basis for membrane attack by defensins
Defensins are small cationic proteins that are involved in innate immune processes in plants as well as humans. In plants, defensins have been shown to deliver significant resistance against plant pathogens such as fungi, however their precise molecular mechanism of action is currently not fully understood. Furthermore, defensins are also able to target cancer cells.
We are currently investigating how defensins are able to attack and perforate cell membranes of pathogens as well as cancer cells. Recognition of phospholipids has been shown to be critical for the ability of defensins to attack target cells, and we are interested in understanding the structural basis for phospholipid recognition as well as membrane attack. Using X-ray crystallography we recently showed that defensins form large oligomeric complexes with phospholipids, thus for the first time shedding light onto the detailed molecular mechanism employed by defensins during innate defence.
Molecular control of cell polarity
The establishment of cell polarity, and correct definition of where top and bottom, front and back as well as left and right are in a cell, is critically important for the formation of tissues in multicellular organisms. Dysregulation of this process is associated with the development of birth defects, more mobile and aggressive cancers as well as viral infections. Correct establishment of the different polarity axis is controlled by a network of scaffolding proteins that integrate signals from a host of cellular signalling pathways. We are interested in understanding the molecular mechanism underlying cell polarity regulation using a range of structural biology techniques including X-ray crystallography, cryo-electron microscopy and small-angle X-ray scattering.
Scribble: Scribble is a large multi-domain scaffold protein that is a key regulator of apico-basal (or top and bottom) polarity, and uses four PDZ domains to interact with a diverse range of proteins to control processes such as tight junction formation and the growth of epithelial tissues. We have now shown that Scribble PDZ domains are highly selective, and discriminate amongst Scribble interacting proteins to finely modulate Scribble signalling. With this information in hand, we are now embarking on studies to understand how different complexes of Scribble with partner proteins influences polarity signalling. Understanding these processes would allow us to tackle dysregulation of Scribble signalling during diseases such as cancer and viral infections, and may provide new avenues for the development of therapeutics that exploit polarity signalling.
Meet the team
Ivan How (co-supervised with Dr Patrick Humbert)
Yang Zhanzhao (co-supervised with Dr Mark Hulett)
Niccolay Madiedo Soler (co-supervised with Dr Ivan Poon)
Bryce Zachary Stewart (co-supervised with Dr Patrick Humbert)
Kimberley Trisann Sequeira
Airah Joyce Javorsky