Fig. 4

Cel7A molecules display diminishing processive behavior on cellulose with increasing lignification. Qdot-labeled Cel7A enzymes were imaged using total internal reflection microscopy at 1 frame/second and positions were fit using a Gaussian point-spread function. A X–Y positions over time for three different Cel7A enzymes on lignin-free cellulose. B Distance from origin versus time for the same three Cel7A enzymes on lignin-free cellulose shown in A. C X–Y positions over time for three different Cel7A enzymes on lignocellulose prepared using 9 mM CA. D Distance from origin versus time for the same three Cel7A enzymes on lignocellulose prepared using 9 mM CA shown in C. For all traces, blue represents the start of the binding event and red indicates the end of the binding event. E Percentage of the total Cel7A enzymes imaged that displayed processive behavior. F Average run length of processive segments; runs less than 10 nm long were excluded from analysis. G Average velocity of processive segments; velocities less than 0.1 nm/s were excluded from analysis. Run lengths and velocities are presented as mean ± SEM. The number of enzymes tracked for each sample were: 0 mM CA, N = 224; 0.11 mM CA, N = 172; 0.33 mM CA, N = 154; 1 mM CA, N = 93; 3 mM CA, N = 88; 9 mM CA, N = 56