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Understanding the mechanism by which cellulases from bacteria, fungi, and protozoans catalyze the digestion of lignocellulose is important for developing cost-effective strategies for bioethanol production. Cel7A from the fungus Trichoderma reesei is a model exoglucanase that degrades cellulose strands from their reducing ends by processively cleaving individual cellobiose units. Despite being one of the most studied cellulases, the binding and hydrolysis mechanisms of Cel7A are still debated. Here, we used single-molecule tracking to analyze the dynamics of 11,116 quantum dot-labeled TrCel7A molecules binding to and moving processively along immobilized cellulose. Individual enzyme molecules were localized with a spatial precision of a few nanometers and followed for hundreds of seconds. Most enzyme molecules bound to cellulose in a static state and dissociated without detectable movement, whereas a minority of molecules moved processively for an average distance of 39 nm at an average speed of 3.2 nm/s. These data were integrated into a three-state model in which TrCel7A molecules can bind from solution into either static or processive states and can reversibly switch between states before dissociating. From these results, we conclude that the rate-limiting step for cellulose degradation by Cel7A is the transition out of the static state, either by dissociation from the cellulose surface or by initiation of a processive run. Thus, accelerating the transition of Cel7A out of its static state is a potential avenue for improving cellulase efficiency., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Quality of life considerations may be an important factor in medical decisions, but it is not known how well physician's assessments match those of their patients. The authors studied the assessments of elderly inpatients (n = 65) and their physicians (n = 50) concerning patient quality of life and resuscitation decisions for the patients' current health situations and for two hypothetical situations. Physicians rated current patient quality of life more negatively than did patients; differences ranged from 0.35 to 0.80 on a 5-point scale with end points labeled "very poor quality of life" and "possible to have good quality of life." Physicians were also less likely to favor resuscitation in the two hypothetical scenarios (p less than 0.01); differences ranged from 0.66 to 1.40 on a 5-point scale with end points labeled "definitely yes" and "definitely no." In both patient and physician groups, quality of life assessments were significantly correlated with resuscitation decisions for some situations but not for others. These results indicate that elderly patients and their physicians may differ on patient quality of life assessments and that these assessments may be associated with resuscitation decisions.