Free energy profile of sugar transport through maltoporin of Escherichia Coli

Abstract

The purpose of my project is to investigate molecular (glucose and maltodextrin) transport in the sugar selective, highly asymmetric maltoporin (LamB) outer membrane channel from E. coli by employing all atom molecular dynamics (MD) simulations. The choice to study maltoporin is motivated by the following facts: (i) it is well characterized experimentally; (ii) it has a highly asymmetric structure as inferred from its high resolution crystal structure (PDB entry 1MPM); and (iii) this is the first all atom MD simulation for this system.

Maltoporin is a trimer of three identical 18-stranded antiparallel β-barrel monomers. In each monomer, the L3 loop folds into the β-barrel to form an hourglass-shaped constriction region with a helical twist that mimics the shape of maltodextrin. This allows maltodextrin to slide through the constriction without any energetically expensive conformational changes. Furthermore, a sequence of aromatic residues, referred to as the "greasy slide", aligned by polar track residues form a specific sugar translocation pathway within the constriction region of the channel.

Our equilibrium MD simulations provided valuable information about the conformational stability of maltoporin, while nonequilibrium SMD simulations revealed the microscopic details of glucose permeation in maltoporin.