diffraction and NMR studies to match against and build upon the models derived from gene sequences. For example, the crystal structure of citrate synthase reveals that there are indeed weaker subunit interactions but also that there is increased surface exposure of hydrophobic residues; the active site has a larger entrance and an arrangement of charged residues which may well facilitate substrate entry and binding (6). This experimental approach is being supported by site-directed mutagenesis studies, and mutants of subtilisin have been produced with improved catalytic efficiency at low temperatures (7). Undoubtedly, within the next few years more cold- active enzyme structures will be solved so that it will be possible to engineer proteins with appropriate properties for exploitation in novel biotechnological applications (2).
1. Russell, N.J. and Hamamoto, T. (1997) Chapter 2 Psychrophiles in Extremophiles: Microbial Life in extreme Environments (K. Horikoshi and W.D. Grant, eds) Wiley-Liss, New York.
2. Russell, N.J. (1997) Biochem. Engin./Biotechnol., Special Volume on Extremophiles (G. Antranikian, ed.), Springer-Verlag, Heidelberg, in press.
3. Feller, G., Narinx, E., Arpigny, J.L., Zekhnini, Z., Swings, J., and Gerday, C. (1996) FEMS Microbiol. Rev., 18, 189-202.
4. Aghajari, N., Feller, G., Gerday, C., and Haser, R. (1997) Prot. Sci., 5, 2128-2129.
5. Rentier-Delrue, F., Mande, S.C., Moyens, S., Terpstra, P., Mainfroid, V., Goraj, K., Lion, M., Hol, W.G., and Martial, J. (1993) J. Mol. Biol., 229, 85-93.
6. Gerike, U., Danson, M.J., Hough, D.W., Russell, N.J., and Taylor, G.L. Acta Crystallog., submitted.
7. Narinz, E., Blaise, E., and Gerday, C. (1997) Prot. Engin. 10, in press.
