Sam Maurer

Graduate Student, Ph.D. Program

MIT, Cambridge, MA.
B.S. Chemical Engineering, 2007

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Research Interest:

Surface Kinetic Mechanisms of Cellulose Destruction

 


sam_butterbull
”Would you rather…eat this entire butter sculpture in one sitting, or be force-fed airline food for 3 months?”

 

sammaurer@gmail.com

 

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Research Summary:

 

 

Here is my thesis research, described using only the 1,000 most common words in the English language.

 

We want to make cars go all the time but we don't want to buy the stuff that makes cars go from far away places. The tall things that we grow in big green fields are made of long trains of stuff that we can turn into some stuff that makes cars go. First, we have to break down the long trains of stuff into small pieces. Then we can make tiny animals (too small to see) eat the small pieces, and some stuff that makes cars go will pop out of their back ends (...kind of). The problem is that no one understands how quickly we can break down the long trains of stuff into small pieces, and this is the most important part. I tried to make a new way of understanding this break-down using numbers.

 

 

 

Here is my thesis research, described using only the three abstracts from my publications.

 

Surface kinetics for cooperative fungal cellulase digestion of cellulose from quartz crystal microgravimetry
J Colloid Interface Sci. 2013 Mar 15, 394, pp 498-508

The kinetic behavior of aqueous cellulase on insoluble cellulose is best quantified through surface-based assays on a well-defined cellulose substrate of known area. We use a quartz crystal microbalance (QCM) to measure the activity of binary mixtures of Trichoderma longibrachiatum cellobiohydrolase I (Cel7A) and endoglucanase I (Cel7B) on spin-coated cellulose films. By extending a previous surface kinetic model for cellulase activity, we obtain rate constants for competitive adsorption of Cel7A and Cel7B, their irreversible binding, their complexation with the cellulose surface, and their cooperative cellulolytic activity. The activity of the two cellulases is linked through the formation of cellulose chain ends by Cel7B that provide complexation sites from which Cel7A effects cellulose chain scission. Although the rate-limiting step in Cel7A activity is complexation, Cel7B activity is limited by adsorption to the cellulose surface. A 2:1 bulk mass ratio of aqueous Cel7A:Cel7B, corresponding to a 4:1 surface mass ratio, effects the greatest rate of cellulose degradation across a range of cellulase concentrations at 25 °C. We find that surface chain-end concentration is a major predictor of Cel7A activity. Disruption of the hydrogen-bonding structure of cellulose by Cel7B enhances the activity of Cel7A on the cellulose surface.

Competitive Sorption Kinetics of Inhibited Endo- and Exoglucanases on a Model Cellulose Substrate
Langmuir, 2012, 28 (41), pp 14598–14608

For the first time, the competitive adsorption of inhibited cellobiohydrolase I (Cel7A, an exoglucanase) and endoglucanase I (Cel7B) from T. longibrachiatum is studied on cellulose. Using quartz crystal microgravimetry (QCM), sorption histories are measured for individual types of cellulases and their mixtures adsorbing to and desorbing from a model cellulose surface. We find that Cel7A has a higher adsorptive affinity for cellulose than does Cel7B. The adsorption of both cellulases becomes irreversible on time scales of 30–60 min, which are much shorter than those typically used for industrial cellulose hydrolysis. A multicomponent Langmuir kinetic model including first-order irreversible binding is proposed. Although adsorption and desorption rate constants differ between the two enzymes, the rate at which each surface enzyme irreversibly binds is identical. Because of the higher affinity of Cel7A for the cellulose surface, when Cel7A and Cel7B compete for surface sites, a significantly higher bulk concentration of Cel7B is required to achieve comparable surface enzyme concentrations. Because cellulose deconstruction benefits significantly from the cooperative activity of endoglucanases and cellobiohydrolases on the cellulose surface, accounting for competitive adsorption is crucial to developing effective cellulase mixtures.

Cellulase Adsorption and Reactivity on a Cellulose Surface from Flow Ellipsometry
Ind. Eng. Chem. Res., 2012, 51 (35), pp 11389–11400

Enzymatic deconstruction of cellulose occurs at the aqueous/cellulose interface. Most assays to explore cellulase activity, however, are performed in bulk solution and, hence, fail to elucidate surface-reaction kinetics. We use flow ellipsometry to quantify the adsorption and surface reactivity of aqueous cellulase on a model cellulose film substrate. The rate of cellulose digestion at the aqueous/solid interface increases with increasing bulk concentration of enzyme, but only up to a plateau corresponding to the maximum adsorption density of cellulase. Kinetic data are analyzed according to a modified Langmuir–Michaelis–Menten framework including both reversible adsorption of cellulase to the cellulose surface and complexation of surface cellulose chains with adsorbed cellulase. At ambient temperature, the molar turnover number is 0.57 ± 0.08 s–1, commensurate with literature values, and the Langmuir adsorption equilibrium constant, characterizing the binding strength of the cellulase, is 0.086 ± 0.026 ppm–1. The rate-determining step in the surface-reaction sequence is complexation of adsorbed cellulase with the solid-cellulose surface. Simultaneous knowledge of sorption and digestion kinetics is necessary to quantify cellulose deconstruction.

 

 

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