Warwick Hillier

Photobioenergetics
Research School of Biological Sciences
Australian National University
Canberra ACT 0200
Australia
Ph: (02) 6125 5894
Fax: (02) 6125 8056

	My Molecular Oxygen site

Information for prospective students

Current position

Fellow

Research Interests:

An overview of the areas of interest to me

• Use of light energy by plants for photochemistry
• Chemistry and catalysis of photosynthetic water oxidation by Photosystem II.
• The molecular organisation of proton pumping in Cytochrome c Oxidase.
• Molecular Biofuels

Photosynthesis:

Is a process that describes the complex biological processes by which solar energy is converted into chemical energy. Central to this function are the photosynthetic reactions centres which reside at the true interface between the physical and biological worlds. The photosynthetic reaction centres (along with the rhodopsin ion pumps) are the only bio-molecular machinery capable of converting light energy into chemical intermediates for biosynthetic reactions. Without such energy conversion life would be limited to chemotropic activity about hydrothermal vents and pools of reductants.

Photosystem II (PSII) is one type reaction centre with pivotal importance to life on earth. PSII is the principle means by which molecular oxygen is generated on earth. The consequences of PSII and its O₂ by-product have had profound influences for the evolution of life. The light-induced formation of O₂ in PSII can be summarized as follows:

2H₂O + 4 hν --(to)---> O₂ + 4H⁺ + 4e^-

This reaction is simple enough to chemically render, however, the chemistry has several remarkable features. In particular, PSII catalyses the most oxidising chemistry in all of biology (>1 volt oxidation) and it does so in a rapid way (>1000 turnovers / s), while maintaining a low thermodynamic barriers, and minimising the generation of reactive oxygen intermediates. This chemistry has evolved over billions of years and “mother nature’s little secrets” are tightly guarded, yet we are slowly learning these.

I am actively involved in understanding of several of these aspects.

• The chemical structure of the enzymatic cofactors that catalyse water oxidation.
• Movement (channelling) of water within proteins.
• Oxidation sequence of a 4 electron oxidation involving 4 metal ions.
• Structure of the PSII and use of pigments for photochemistry.
• Construction and design of model protein (maquette) systems.
• Evolution of this system on earth and exobiology (astrobiology) considerations.

Respiration

Is another fundamental process in biology. All living things respire by reducing complex molecules to simple ones (down the electrochemical gradient) and in the process releasing energy for what ultimately is converted into ATP. Much of the respiration on the planet operates in the presence of oxygen (aerobic respiration) and is therefore intimately dependent on the photosynthesis reaction pathways.

One protein complex which gains a free (thermodynamic) ride from O₂ is the respiratory Cytochrome c Oxidase (CCO) protein - also called complex IV. This enzyme is able to use O₂ as a powerful reductant to drive electron transfer reactions and concomitantly pump H⁺ s. This is a true molecular machine. This protein is particularly important enzymatically and at a chemical level operates in a highly efficient manner with rapid turn over rates, O₂ is reduced with very low over-potentials, the catalysis uses non-precious metals (Fe and Cu) at a bimolecular site, and there is minimal generation of reactive oxygen intermediates in the 4-electron reduction chemistry.

I am actively involved in understanding of several of these aspects.

• The redox titration of the cofactors.
• Oxygen chemistry.
• Proton pathways and substrate channels.
• Oxygen binding affinity (Km).
• Feedback mechanisms for H⁺ coupling.

A variety of techniques are employed emphasising spectroscopy and a biodiversity of biological material. Principle studies involve stable isotope mass spectrometry, vibrational spectroscopy, optical spectroscopy and kinetics. Along the way we dabble in molecular biology, protein expression, protein chromatography, spectroscopy, electrochemistry, and….other things as needed.

Selected Publications

Richard J. Debus, Melodie A. Strickler, Lee M. Walker, and Warwick Hillier (2005) No Evidence from FTIR Difference Spectroscopy that Aspartate-170 of the D1 Polypeptide Ligates a Mn Ion that Undergoes Oxidation During the S0 to S1, S1 to S2, or S2 to S3 Transitions in Photosystem II. Biochemistry, 44, 1367-1374. (pdf)

Chu , H.-A., Hillier, W, & Debus, R. T. (2004) FTIR assignment of D1-Ala 244 at the C-terminus as a ligand to the Mn4 cluster of the of oxygen evolving complex of Photosystem II. Biochemistry, 43, 3152-3166. (pdf)

Hillier, W, & Wydrzynski, T. (2004) Substrate Water Interactions Within the Photosystem II Water Oxidising Complex. Phys. Chem. Chem. Phys., 6, 4882-4889. (pdf)

Hillier, W., & Babcock, G. T. (2001) Photosynthetic Reaction Centres. Plant Physiology 125, 33-37. (pdf)

Hillier, W., & Wydrzynski, T. (2000) The Affinities For The Two Substrate Water Binding Sites In The O2 Evolving Complex of Photosystem II Vary Independently During S-State Turnover. Biochemistry 39, 4399-4405. (pdf)

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