PRELIMINARY CRYSTALLOGRAPHIC STUDIES OF TRIOSEPHOSPHATE ISOMERASE FROM THE HYPERTHERMOPHILIC ARCHAEON PYROCOCCUS WOESEI. Graeme S. Bell, Rupert J.M. Russell, David W. Hough, Michael J. Danson and Garry L. Taylor. School of Biology and Biochemistry, University of Bath, Bath, BA2 7AY, U.K.

Structural studies on triosephosphate isomerase (TIM), isolated from P. woesei, are being carried out to further our knowledge of archaeal enzymes. In addition, as P. woesei exhibits an optimal growth temperature of 100^oC, elucidation of enzymes from this organism will hopefully highlight structural features which could confer hyperthermostability.

The 8-stranded [[alpha]]/[[beta]] barrel, first discovered in chicken TIM, is the most frequently occurring motif found in proteins , and is a common structural scaffold for enzymes which perform a diverse range of functions. For this reason it is a good model enzyme to select for comparative study ; there are now six known 3-D structures of TIM from both bacterial and eukaryal sources (both mesophilic and thermophilic), however, there is no data yet on the structure of archaeal TIMs.

The gene of P. woesei TIM has been cloned and sequenced and the enzyme has been overexpressed in Escherichia coli, with subsequent purification to homogeneity. (Prof. Reinhardt Hensel, University of Essen - private communication). The derived protein sequence, comprising 224 residues, is the shortest TIM sequence known yet. In addition, TIM from P. woesei has been found to exist as a homotetramer of 100kDa, contrary to all known bacterial and eukaryal TIMs, which are homodimeric.

To extend this work further, crystallisation studies have been carried out on the recombinant protein, and preliminary crystallographic data will also be presented.