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Journal of Bacteriology, March 2001, p. 1974-1982, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1974-1982.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Effects of Ribosomes and Intracellular Solutes on Activities and Stabilities of Elongation Factor 2 Proteins from Psychrotolerant and Thermophilic Methanogens

Torsten Thomas,1 Naresh Kumar,2 and Ricardo Cavicchioli1,*

School of Microbiology and Immunology1 and School of Chemistry,2 The University of New South Wales, Sydney, UNSW, 2052, Australia

Received 15 September 2000/Accepted 21 December 2000

Low-temperature-adapted archaea are abundant in the environment, yet little is known about the thermal adaptation of their proteins. We have previously compared elongation factor 2 (EF-2) proteins from Antarctic (Methanococcoides burtonii) and thermophilic (Methanosarcina thermophila) methanogens and found that the M. burtonii EF-2 had greater intrinsic activity at low temperatures and lower thermal stability at high temperatures (T. Thomas and R. Cavicchioli, J. Bacteriol. 182:1328-1332, 2000). While the gross thermal properties correlated with growth temperature, the activity and stability profiles of the EF-2 proteins did not precisely match the optimal growth temperature of each organism. This indicated that intracellular components may affect the thermal characteristics of the EF-2 proteins, and in this study we examined the effects of ribosomes and intracellular solutes. At a high growth temperature the thermophile produced high levels of potassium glutamate, which, when assayed in vitro with EF-2, retarded thermal unfolding and increased catalytic efficiency. In contrast, for the Antarctic methanogen adaptation to growth at a low temperature did not involve the accumulation of stabilizing organic solutes but appeared to result from an increased affinity of EF-2 for GTP and high levels of EF-2 in the cell relative to its low growth rate. Furthermore, ribosomes greatly stimulated GTPase activity and moderately stabilized both EF-2 proteins. These findings illustrate the different physiological strategies that have evolved in two phylogenetically related but thermally distinct methanogens to enable EF-2 to function satisfactorily.

* Corresponding author. Mailing address: School of Microbiology and Immunology, The University of New South Wales, Sydney, UNSW, 2052, Australia. Phone: 61-2-9385-3516. Fax: 61-2-9385-2742. E-mail: r.cavicchioli{at}unsw.edu.au.

Journal of Bacteriology, March 2001, p. 1974-1982, Vol. 183, No. 6
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.6.1974-1982.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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