Maltoporin, a protein residing in the outer membrane of Gram negative bacteria, facilitates the diffusion of linear maltooligosaccharides across the membrane. At equilibrium maltohexaose is bound at the channel constriction as revealed by crystallography. A multitude of hydrophobic and hydrogen-bonding interactions with the protein are observed. During sugar translocation these interactions have to be broken. The movement of the sugar maltohexaose (composed of 6 glucose moeities) through the pore has been studied by computer simulations, using the Conjugate Peak Refinement(CPR) algorithm. The figure on the right shows 4 successive frames taken along the reaction path.  The sugar is colored in yellow (with one glucose unit colored in cyan), the protein residues of the pore are shown in green.

 The following video shows a trajectory of the 'register shift', the movement of the sugar by one glucose moeity towards the periplasm. The arrangement of the polar groups in the channel allows a continuous breaking and reforming of hydrogen-bonds. Thus the sugar is at any instance well bound to the channel and no high energy barriers are encountered.

 Download the movie , ~3Mb
(depending on the MPEG-viewer declared in your WEB-brower, you may have to click on the black box that will appear).

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