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Crystal structure of the EutL shell protein of the ethanolamine ammonia lyase microcompartment.

ABSTRACT: Bacterial microcompartments (BMCs) are specialized organelles that use proteinaceous membranes to confine chemical reaction spaces. The ethanolamine ammonialyase microcompartment of Escherichia coli represents such a class of cytosolic organelles that enables bacteria to survive on small organic molecules such as ethanolamine as the sole source for carbon and nitrogen. We present here the crystal structure of the shell protein EutL at 2.2-A resolution. With 219 residues, it is the largest representative of this BMC's shell proteins. In the crystal, EutL forms a trimer that exhibits a hexagonally shaped tile structure. The tiles arrange into a tightly packed 2D array that is likely to resemble the proteinaceous membrane of the intact BMC. In contrast to other BMC shell proteins, which have only 1 pore per tile, EutL exhibits 3 pores per tile, thereby significantly increasing the overall porosity of this protein membrane. Each of the individual pores is lined with negatively charged residues and aromatic residues that are proposed to facilitate passive transport of specific solutes. The characteristic shape of the hexagonal tile, which is also found in the microcompartments of carbon-fixating bacteria, may present an inherent and fundamental building unit that may provide a general explanation for the formation of differently sized microcompartments.

SUBMITTER: Sagermann M

PROVIDER: S-EPMC2690006 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Crystal structure of the EutL shell protein of the ethanolamine ammonia lyase microcompartment.

Sagermann Martin M Ohtaki Akashi A Nikolakakis Kiel K

Proceedings of the National Academy of Sciences of the United States of America 20090518 22

Bacterial microcompartments (BMCs) are specialized organelles that use proteinaceous membranes to confine chemical reaction spaces. The ethanolamine ammonialyase microcompartment of Escherichia coli represents such a class of cytosolic organelles that enables bacteria to survive on small organic molecules such as ethanolamine as the sole source for carbon and nitrogen. We present here the crystal structure of the shell protein EutL at 2.2-A resolution. With 219 residues, it is the largest repres ...[more]

PMID: 19451619

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Project description:The adenosylcobalamin- (coenzyme B12) dependent ethanolamine ammonia-lyase (EAL) plays a key role in aminoethanol metabolism, associated with microbiome homeostasis and Salmonella- and Escherichia coli-induced disease conditions in the human gut. To gain molecular insight into these processes toward development of potential therapeutic targets, reactions of the cryotrapped (S)-2-aminopropanol substrate radical EAL from Salmonella typhimurium are addressed over a temperature (T) range of 220-250 K by using T-step reaction initiation and time-resolved, full-spectrum electron paramagnetic resonance spectroscopy. The observed substrate radical reaction kinetics are characterized by two pairs of biexponential processes: native decay to diamagnetic products and growth of a non-native radical species and Co(II) in cobalamin. The multicomponent low-T kinetics are simulated by using a minimal model, in which the substrate-radical macrostate, S?, is partitioned by a free-energy barrier into two sequential microstates: 1) S1?, a relatively high-entropy/high-enthalpy microstate with a protein configuration that captures the nascent substrate radical in the terminal step of radical-pair separation; and 2) S2?, a relatively low-enthalpy/low-entropy microstate with a protein configuration that enables the rearrangement reaction. The non-native, destructive reaction of S1? at T ? 250 K is caused by a prolonged lifetime in the substrate-radical capture state. Monotonic S? decay over 278-300 K indicates that the free-energy barrier to S1? and S2? interconversion is latent at physiological T-values. Overall, the low-temperature studies reveal two protein-configuration microstates and connecting protein-configurational transitions that specialize the S? macrostate for the dual functional roles of radical capture and rearrangement enabling. The identification of new, to our knowledge, intermediate states and specific protein-fluctuation contributions to the reaction coordinate represent an advance toward development of novel therapeutic targets in EAL.

Dataset Information

Crystal structure of the EutL shell protein of the ethanolamine ammonia lyase microcompartment.

Publications

Crystal structure of the EutL shell protein of the ethanolamine ammonia lyase microcompartment.

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