Translocation mechanism of long sugar chains across the maltoporin membrane channel.
Maltoporin allows permeation of long maltodextrin chains. It tightly binds the amphiphilic sugar, offering both hydrophobic interactions with a helical lane of aromatic residues and H bonds with ionic side chains. The minimum-energy path of maltohexaose translocation is obtained by the conjugate peak refinement method, which optimizes a continuous string of conformers without applying constraints. This reveals that the protein is passive while the sugar glides screw-like along the aromatic lane. Near instant switching of sugar hydroxyl H bond partners results in two small energy barriers (of approximately 4 kcal/mol each) during register shift by one glucosyl unit, in agreement with a kinetic analysis of experimental dissociation rates for varying sugar chain lengths. Thus, maltoporin functions like an efficient translocation "enzyme," and the slow rate of the register shift (approximately 1/ms) is due to high collisional friction.
Dutzler
Raimund
R
Department of Structural Biology, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
Schirmer
Tilman
T
Karplus
Martin
M
Fischer
Stefan
S
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability; D006860:Hydrogen Bonding; D007700:Kinetics; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D011134:Polysaccharides / Q000737:chemistry* / Q000378:metabolism*; D018272:Porins; D011485:Protein Binding; D011487:Protein Conformation; D011991:Receptors, Virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D009844:Oligosaccharides; D011134:Polysaccharides; D018272:Porins; D011991:Receptors, Virus; C016532:maltoporins; C016549:maltohexaose