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An RND-Type Efflux System in Borrelia burgdorferi Is Involved in Virulence and Resistance to Antimicrobial Compounds

Figure 4

Comparison of the periplasmic tunnel entrance of E. coli TolC with the modeled structure of Borrelia BesC and a model of the Borrelia efflux pump.

The backbone of the peptide chains of the three monomers are colored differently. Side chains are omitted except those lining the tunnel entrance. These are D371 and D374 in TolC (A) and D363 and K366 in BesC (B) or those involved in forming the circular network in TolC - D153, Y362, and R367. (C) The channel-tunnel BesC is colored red, the adaptor protein BesA is shown in yellow and the RND transporter in green. Structures of all three components are modeled and formed according to existing models [28],[82],[83]. The model of the adaptor protein BesA shows just residues 38–219 of the mature chain. The remaining parts of the protein are not modeled because of the missing template. In this model the complex is comprised of three adaptor protein protomers. It should be mentioned that there are other models proposed suggesting six adaptor protein protomers per efflux apparatus [31],[59]. Note that the adaptor proteins do not have the alpha-helical domain, which is thought to interact with the helices of the tunnel region of the outer membrane component in other bacterial efflux pumps.

Figure 4