Biophysical Society Thematic Meeting | Hamburg 2022

Biophysics at the Dawn of Exascale Computers

Poster Abstracts

24-POS Board 24 DEMONSTRATING THE FUNCTION OF THE SURFACE-EXPOSED LIPOPROTEIN BTUG IN EFFICIENT B 12 TRANSPORT IN ASSOCIATION WITH THE OUTER- MEMBRANE BTUB PROTEIN Kalyanashis Jana 1 ; Javier Abellón-Ruiz 2 ; Bert van den Berg 2 ; Ulrich Kleinekathöfer 1 ; 1 Jacobs University Bremen, 1Department of Physics & Earth Sciences, Bremen, Germany 2 Newcastle University, 2Biosciences Institute, Faculty of Medical Sciences, Newcastle upon Tyne, United Kingdom BtuB, a TonB-dependent transporter, is an outer membrane protein in Gram-negative bacteria that enables the active transport of cyanocobalamin (vitamin B 12 ) and essential nutrients (1). The protein consists of a channel with 22 β -strands combined with a large N-terminal domain, the luminal domain, folded back into and blocking the interior of the barrel. Substrate binding changes the conformational equilibrium in the Ton box as well as the luminal domain to favor an unfolded state that facilitates substrate translocation through BtuB (1–3). A newly determined BtuBG crystal structure purified from Bacteroides the taiotaomicron has been considered for the present computational study. The BtuG, a surface-exposed lipoprotein, adopts a seven- bladed β - propeller fold. The BtuG is strongly connected to the BtuB protein through a hinge loop and can move away from BtuB in a hinge-like fashion (4, 5). We explore how the BtuG protein moves away from BtuB protein and the role of BtuG in the transport of the large B 12 molecule. To explore the B 12 acquisition mechanism, unbiased molecular dynamics (MD) along with multiple walker well-tempered metadynamics (WTMtD) simulations have been carried out. The MD simulation results demonstrate that the BtuBG protein transports cyanocobalamin through a pedal-bin mechanism: the substrate first binds to the open BtuG lid before moving to the BtuB binding site. To this end, multiple walker WTMtD simulations have been employed to determine free energy for the anticipated B 12 transport from the BtuG to BtuB active site cavity.

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