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Characterization of interactions for BtuB, Colicin E3, and HslT Mills, Allan

Abstract

The outer membrane of Gram-negative bacteria acts as a physical barrier against the dangers of the extracellular environment. The outer membrane contains a number of porins and transporters to facilitate the import of nutrients while simultaneously protecting cells from extracellular assault. How these proteins transport nutrients and how they can be subverted are still areas of investigation. In the first study the mechanisms of transport through the vitamin B₁₂ transporter BtuB is investigated. BtuB was found to interact in a 1:1 molar ratio with the inner membrane protein TonB, which is required for transport of vitamin B₁₂ (cobalamin). Binding of TonB, in turn, alters the binding dynamics of the ligand with BtuB and slows the dissociation of ligand. In the second study transport of the antimicrobial protein colicin E3 across the outer membrane was investigated. Colicin E3 is a ribosomal nuclease that exists in a complex with an inhibitor, immunity protein Im3. Denaturation of colicin E3 was found to facilitate the interaction of the colicin with its outer membrane binding partners by dissociation of Im3. Release of Im3 from colicin E3 allows the nuclease domain of colicin E3 to interact with lipopolysaccharide as part of the transport process. Finally, OmpC and HslT from the Gram-negative Salmonella enterica serovar Typhimurium are hypothesized to interact to protect persistent infectious cells from the oxidizing assault of the immune system. No direct interaction between OmpC and HslT was detectable, possible explanations for this lack of interaction are discussed. These results are discussed in the context of how both ligands and antimicrobial compounds are transported across the outer membrane.

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