Translocation mechanism of long sugar chains across the maltoporin membrane channel

Structure. 2002 Sep;10(9):1273-84. doi: 10.1016/s0969-2126(02)00811-0.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism
  • Biological Transport
  • Cell Membrane / metabolism*
  • Cell Membrane Permeability
  • Hydrogen Bonding
  • Kinetics
  • Models, Molecular
  • Oligosaccharides / chemistry
  • Oligosaccharides / metabolism
  • Point Mutation / genetics
  • Polysaccharides / chemistry*
  • Polysaccharides / metabolism*
  • Porins
  • Protein Binding
  • Protein Conformation
  • Receptors, Virus / chemistry
  • Receptors, Virus / genetics
  • Receptors, Virus / metabolism*
  • Structure-Activity Relationship
  • Thermodynamics


  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • Oligosaccharides
  • Polysaccharides
  • Porins
  • Receptors, Virus
  • maltoporins
  • maltohexaose