Samantha Ziegler

National Renewable Energy Laboratory

ABSTRACT

AdhEs are multifunctional/multidomain enzymes with alcohol and aldehyde dehydrogenase activities that form higher order structures called spirosomes in some bacteria and unicellular algae. The alcohol dehydrogenase and aldehyde dehydrogenase activities are separated onto individual domains of the AdhE, however a channel has been predicted to form between the two active sites in the extended spirosome from E. coli. Additionally, AdhEs have been shown to behave differently when heterologously expressed in different thermophiles. We aim to understand the function of the spirosome assembly in several thermophilic bacteria and the changes that occur when heterologously expressed in a different host. Here, we use electron microscopy and biochemical techniques to compare C. thermocellum and E. coli AdhE spirosomes and their levels of activity to determine how they are impacted when expressed in a different environment. We find that while E. coli and C. thermocellum AdhE form spirosomes, T. saccharolyticum AdhE lacks this ultrastructure. In addition, the native state of the protein differs between E. coli and C. thermocellum, regardless of endogenous versus exogenous expression. We hope that by furthering understanding of the complex architecture of these proteins, we can begin to decipher why AdhE-based ethanol production is better in some organisms over others.

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