Current Research Interests

 

 

1. CLIC proteins, ezrin, radixin, moesin & the coupling of membranes to the actin cytoskeleton

CLIC proteins

CLIC1

 

Figure 1. Structural transition in CLIC1. (A) soluble monomer CLIC1 structure
compared to (B) the half dimer structure observed after oxidation.

CLIC proteins are unusual in that they exist in both globular and integral membrane states. The CLICs are highly conserved in vertebrates with homologues in most, if not all, metazoa. CLICs can form anion (chloride) channels in vitro and in vivo. Our goal is to gain a comprehensive understanding of the CLIC proteins in collaboration with Sam Breit (St. Vincent's Centre for Applied Medical Research), Michele Mazzanti (University of Milan), Louise Brown (Macquarie University) and Stella Valenzuela (University of Technology Sydney). We have determined several crystal structures of CLIC proteins in the soluble form. In addition, we have discovered a dramatic structural change in CLIC1 that is stabilised by oxidation. Our current goal is to determine the structure of the integral membrane form of a CLIC protein as well as the structures of complexes with partner proteins.

Controlling membrane remodelling in mammalian cells

We are establishing the link between CLICs, ERM proteins, Rho GTPases and the cortical actin cytoskeleton. In collaboration with Till Böcking (UNSW), we are developing single molecule approaches to probe the interactions of these proteins in artificial systems and cells. The assembly of cellular complexes may involve similar mechanisms to those we are modelling for cell division.

Metamorphic proteins

It was believed that a protein sequence would define a single, well-defined three-dimensional structure. Using X-ray crystallography, we have discovered that the protein CLIC1 can adopt several well-defined structures. Along with the concurrent discovery of two other such proteins, this has led to the concept of metamorphic proteins. Currently we are focusing on understanding the structure, function and evolution of the CLIC protein family. In particular, we aim to determine the structure of the integral membrane state of the CLIC ion channel.

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2. Does quantum mechanics play a non-trivial role in biology?

Quantum beats in the spectroscopy of light harvesting proteins

Proteins were assumed to function via classical physics with quantum effects playing trivial roles. In collaboration with Greg Scholes (University of Toronto) we have shown that certain algal light harvesting proteins show spectroscopic signatures of long-lived quantum coherence under near physiological conditions. Along with parallel discoveries, this has led to intense research activity aimed at determining the physical mechanism behind the observed long-lived oscillations in the 2D electronic spectra and whether quantum electronic coherence plays a role in photosynthetic light harvesting.

 

PE545 crystal   PE545 structure

Figure 2. PE545 crystal and structure

Cryptophyte light harvesting proteins

Cryptophytes are an unusual type of single-celled algae that have resulted from the endosymbiosis of a red algal cell inside a eukaryotic host. Like cyanobacteria and red algae, the cryptophytes have preserved a light harvesting system based on phycobiliproteins that are members of the globin fold superfamily. Unlike cyanobacteria and red algae, the cryptophyte phycobiliproteins are soluble and reside in the lumen on the thylakoid. We are using crystallography to unravel the mechanism by which these proteins trap light photons and transfer the energy to the membrane bound photosystem. We are collaborating with Greg Scholes (University of Toronto) and Jeff Davis (Swinburne University of Technology) whose groups are probing the light harvesting system via ultrafast laser spectroscopy. Our crystals of the light harvesting proteins diffract to ultra high resolution (<1Å).

Evolution of light harvesting proteins

The evolution of the cryptophyte light harvesting proteins has involved a radical rearrangement of the quaternary structure of the ancestral phycobilisome antenna complex from red algae and cyanobacteria. This rearrangement alters energy transfer within the light harvesting protein and between it and the membrane bound photosystems. We are tracking the evolution of light harvesting architectures within the cryptophytes in collaboration with Roger Hiller (Macquarie University), Beverley Green (University of British Columbia)and Kerstin Hoef-Emden(University of Cologne).Our aim is to characterise the structures of these complexes and determine the relationship between sequence, structure and spectroscopic properties.

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3. How do molecular machines work?

Protein machines function as motors, but there is no satisfactory explanation as to how they transduce energy. We are part of an international group to try and build a protein based molecular motor from non-motor components (Heiner Linke, Lund University; Dek Woolfson, University of Bristol; Nancy Fordeand Martin Zuckermann, Simon Fraser University; Beth Bromley, Durham University; Gerhard Blab, Utrecht University; and Till Böcking, UNSW). The aim is to test whether protein motors work by rectifying noise (ratchet). We have designed several candidate motors and we are currently building them using molecular biology and semi-synthetic approaches.

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4. How do proteins know where they are in cells?

The interior of any cell is far from homogeneous. What produces the patterns of protein distributions? Is there a map? Using the concept of Turing patterns, we are modelling protein systems that determine the site of cell division. We have identified a minimal set of biochemical reactions that via a reaction-diffusion mechanism create stable patterns that account for observed cell division. The model relates cell geometry to protein distributions. This is a collaboration with Chris Angstmann (UNSW). Additionally, we are collaborating with Iain Duggan and Liz Harry (University of Technology Sydney) to examine cell division in both archaea and bacteria.

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5. Archaea, nucleic acid binding proteins & cold adaptation

Most of the biosphere (>80%) is cold (permanently below 5°C), thus, a large proportion of organisms have evolved to thrive in cold environments. We are collaborating with Rick Cavicchioli (UNSW), who has established a comprehensive program to determine the mechanisms by which archaea adapts to cold environments. We are looking at factors that allow proteins to function at low temperature as well as molecular chaperones and protein folding in psychrophiles.  We have determined the crystal structure of a monomeric form of the archaeal chaperonin, Cpn60, from the Antarctic psychrophile Methanococcoides burtonii.  We have discovered that nucleic acid binding proteins play an important role in stabilising nucleic acids at low temperatures.

RNPs. 

LsmSmF

Figure 3. Archaeal Lsm and Yeast SmF

Ribonucleoprotein complexes form some of the most ancient, central machines in extant organisms. The Sm/Lsm proteins from a core ring structure that appears in many RNPs in all three domains of life. In collaboration with Bridget Mabbutt (Macquarie University), we are using X-ray crystallography to gain a better understanding of these ring complexes in both archaea and eukarya.