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The temperatures needed to denature enzymes from thermophilic organisms have been measured by melting the two analogous protein domains E2(sub cd) and CenA(sub P30). The former is the isolated catalytic domain of cellulase E2 of Thermomonospora fusca while the latter is the analogous domain of the cellulase CenA from Cellulomonas fumi. Results indicate that T. fusca has a melting temperature (Tm) of 72.2 C, a van't Hoff enthalpy of unfolding (deltaH(sub VH)) of 190 kcal/mol and an entropy of unfolding (deltaS(sub u)) of 0.55 kcal/mol*K. C. fumi has a Tm of 56.4 C, a deltaH(sub VH) of 107 kcal/mol and a deltaS(sub u) of 0.32 kcal/mol*K

A study was conducted to determine the solution structure of a 110 amino acid cellulose-binding domain from Cex, a beta-1,4-glycanase from the bacterium Cellulomonas fimi. Multidimensional, multinuclear nuclear magnetic resonance spectroscopy was used in tandem with dynamic simulated annealing to determine the structure. The structures computed had an average root-mean-square deviation about the mean structure of 0.41 angstrom for backbone atoms and 0.67 angstrom for heavy atoms when superimposed on the secondary structural elements.

Determination of the high-resolution crystal structure of the Cex catalytic domain in Cellulomonas fimi reveals that the crystal structure contains 2400 protein atoms, 0.217 R-factor and 45 water molecules at a resolution of 1.8 Angstrom units. The folding of the protein into an eight-parallel-stranded alpha/beta-barrel is new for the microbial beta-glycanase Cex. While the active site exists as an open cleft on the alpha/beta-barrel carboxy-terminal, the hydrogen bonding network in the domain stabilizes the ionization states of vital residues for regulating the equilibrium of the reactions.