Our major goal in this work is to improve our understanding of the structural and functional adaptations of the enzymes that fit them for function in Antarctic fish and how these adaptations compare with those of related fish from more temperate waters. In the long-term we plan to examine a number of proteins so that we can produce a general picture of how low temperature affects protein structure and function. This work will also deepen our understanding of the mechanisms by which ligands interact with enzymes and will improve our knowledge of how proteins fold.
In addition to the general question of how proteins fold to allow activity at low temperatures, we are interested in the specific question of the nature of the structure of antifreeze glycopeptides. We wish to answer this question by growing crystals of these proteins and solving the structure by X-ray crystallography.
Proteins in Antarctic fish continue functioning despite being exposed to temperatures below that at which most proteins lose activity. Decreased temperatures have effects in two main areas in which we are interested; changes to ligand-binding, and the effects of temperature on overall protein stability.
Much of the reduction of enzyme activity with temperature can be ascribed to a reduction of thermal motion. At low temperatures, binding of ligands is likely to be of a higher affinity, and the enzyme itself is less likely to "breathe". The consequence of increased affinity of ligand-binding is complex. Although the substrate may well bind more readily to an enzyme (possibly associated with a reduced Km), the tightness of binding may inhibit the conformational changes necessary for the catalytic cycle to occur. Furthermore, once product is formed, it may have a higher affinity for the enzyme at lower temperatures, and thus be less likely to leave the complex, reducing the catalytic efficiency of the enzyme. We might expect then that enzymes that are adapted for activity in the cold will show reduced ligand-binding interactions; particularly binding to product. It is difficult to assess the nature of the binding interactions that are likely to be altered. Whether there is a selective loss of hydrophobic interactions, which tend to be favoured at low temperatures, hydrogen bond or van der Waals interactions, or instead a generalized reduction of binding interactions is something that can only be determined by experiment.
The general decrease in thermal motion at lower temperatures will also have important consequences for enzyme action. Catalytic activity in enzymes is almost always associated with movement of one sort or another. Indeed, the introduction of disulfide bridges into enzymes in an effort to increase their thermal stability has sometimes been associated with a loss of catalytic activity as the introduced bridges have been too effective in constraining thermal motion. Experience with proteins from thermophilic organisms where the requirement for increased thermal stability is paramount, has suggested that more efficient hydrophobic packing is an effective way to increase the thermal stability. These studies have helped to highlight the importance of hydrophobic interactions in determining protein folding.
Cold-adapted proteins are faced with the converse problem. The reduced temperature is likely to make them too stable and unable to undergo the conformational changes associated with catalysis. Determining the structure of cold-adapted LDH will allow us to determine the changes that are likely to be responsible for changing the thermal stability to allow conformational change; whether it be decreased efficiency of hydrophobic packing in the core of the protein, a reduction of hydrogen bonding or the introduction of electrostatic interactions serving to reduce the protein stability.
Anna C Seybold, David A Wharton, Michael A S Thorne, and Craig J Marshall., Establishing RNAi in a Non-Model Organism: The Antarctic Nematode Panagrolaimus sp. DAW1., PLoS ONE 2016 vol. 11 (11) p. e0166228., Link »
Craig J Marshall, Koli Basu, and Peter L Davies., Ice-Shell Purification of Ice-Binding Proteins., Cryobiology 2016., Link »
Chiara Papetti, Heidrun S Windisch, Mario La Mesa, Magnus Lucassen, Craig Marshall, and Miles D Lamare., Non-Antarctic notothenioids: Past phylogenetic history and contemporary phylogeographic implications in the face of environmental changes., Marine Genomics 2015., Link »
C W Marshall, D Chagné, O Deusch, N Gruenheit, J McCallum, D Bergin, P J Lockhart, and P L Wilcox., A DNA-based diagnostic for differentiating among New Zealand endemic Podocarpus., Tree Genetics and Genomes 2015 vol. 11 (4)., Link »
MAS Thorne, H Kagoshima, M S Clark, and C J Marshall, Molecular analysis of the cold tolerant Antarctic nematode, Panagrolaimus davidi, PLoS ONE 9(8): e104526, Link »
T. C. Hawes, C J Marshall, and D A Wharton, A 9kDa antifreeze protein from the Antarctic springtail, Gomphiocephalus hodgsoni., Cryobiology , Link »
M R Raymond, D A Wharton, and C J Marshall, Nematodes from the Victoria Land coast, Antarctica and comparisons with cultured Panagrolaimus davidi, Antarctic Science 2014 vol. 26 (1) pp. 15-22, Link »
M R Raymond, D A Wharton, and C J Marshall, Factors determining nematode distributions at Cape Hallett and Gondwana station, Antarctica, Antarctic Science 2013 vol. 25 (3) pp. 347-357, Link »
Mélianie R Raymond, David A Wharton, and Craig J Marshall, Nematodes from the Victoria Land coast, Antarctica and comparisons with cultured Panagrolaimus davidi, Antarctic Science 2013 pp. 1-8, Link »
Mélianie R Raymond, David A Wharton, and Craig J Marshall, Factors determining nematode distributions at Cape Hallett and Gondwana station, Antarctica, Antarctic Science 2013 pp. 1-11, Link »
Anton P AP Van de Putte, Karel K Janko, Eva E Kasparova, Gregory E GE Maes, Jennifer J Rock, Philippe P Koubbi, Filip A M FA Volckaert, Luká L Choleva, Keiron P P KP Fraser, Jerzy J Smykla, Jeroen K J JK Van Houdt, and Craig C Marshall, Comparative phylogeography of three trematomid fishes reveals contrasting genetic structure patterns in benthic and pelagic species., Marine Genomics 2012 vol. 8 pp. 23-34, Link »
L.A. MacKenzie, A.I. Selwood, and C Marshall, Isolation and characterization of an enzyme from the Greenshell mussel Perna canaliculus that hydrolyses pectenotoxins and esters of okadaic acid, Toxicon 2012 vol. 60 (3) pp. 406-419, Link »
T C Hawes, C J Marshall, and D A Wharton, Ultraviolet radiation tolerance of the Antarctic springtail, Gomphiocephalus hodgsoni, Antarctic Science 2012 vol. 24 (2) pp. 147-153, Link »
T. C. Hawes, C J Marshall, and D A Wharton, Antifreeze proteins in the Antarctic springtail, Gressittacantha terranova, Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 2011 vol. 181 (6) pp. 713-719, Link »
Marshall, C. J. (2012) Aspects of Protein Cold Adaptation in Antarctic Fish. In Adaptation and Evolution in Marine Environments (Verde, C., and di Prisco, G., eds.), pp 143155, Springer-Verlag, Berlin Heidelberg.
Janko, K., Marshall, C., Musilová, Z., Houdt, J. V., Couloux, A., Cruaud, C. and Lecointre, G. (2011) Multilocus analyses of an Antarctic fish species flock (Teleostei, Notothenioidei, Trematominae): Phylogenetic approach and test of the early-radiation event. Mol Phylogenet Evol, Elsevier 60, 305316.