Ej. Jervis et al., SURFACE-DIFFUSION OF CELLULASES AND THEIR ISOLATED BINDING DOMAINS ONCELLULOSE, The Journal of biological chemistry, 272(38), 1997, pp. 24016-24023
The surface diffusion rate of bacterial cellulases from Cellulomonas f
imi on cellulose was quantified using fluorescence recovery after phot
obleaching analysis. Studies were performed on an exo-beta-1-4-glycana
se (Cex), an endo-beta-1-4-glucanase (CenA), and their respective isol
ated cellulose-binding domains (CBDs). Although these cellulose-bindin
g domains hind irreversibly to microcrystalline cellulose, greater tha
n 70% of bound molecules are mobile on the cellulose surface. Surface
diffusion rates are dependent on surface coverage and range from a low
of 2 x 10(-11) to a maximum of 1.2 x 10(-10) cm(2)/s. The fraction of
mobile molecules increases only slightly with increasing fractional s
urface coverage density. Results demonstrate that the packing of C. fi
mi cellulases and their isolated binding domains onto the cellulose su
rface is a dynamic process. This suggests that the exclusion of potent
ial CBD binding sites on the cellulose due to steric effects of neighb
oring bound CBDs may not fully explain the apparent negative cooperati
vity exhibited in CBD adsorption isotherms. Comparison with the kineti
cs of cellulase hydrolysis of crystalline substrate suggests that surf
ace diffusion rates do not limit cellulase activity.