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Structural basis for sugar translocation through maltoporin channels at 3.1 A resolution
T Schirmer1, T A Keller, Y F Wang
1Department of Structural Biology, University of Basel, Switzerland.
Science (New York, N.Y.)
|January 27, 1995
Summary
Trimeric maltoporin (LamB protein) from E. coli forms a beta-barrel channel. This structure facilitates maltodextrin diffusion, with aromatic residues guiding sugars through a constriction.
Area of Science:
- Structural biology
- Microbiology
- Biochemistry
Background:
- Gram-negative bacteria outer membranes possess porin channels for nutrient transport.
- Maltoporin (LamB protein) is a key trimeric porin facilitating maltodextrin diffusion.
- Understanding porin structure-function is crucial for bacterial physiology.
Purpose of the Study:
- To elucidate the high-resolution crystal structure of Escherichia coli maltoporin.
- To identify structural features responsible for maltodextrin translocation.
- To propose a mechanism for sugar transport across the outer membrane.
Main Methods:
- X-ray crystallography of trimeric maltoporin from E. coli.
- Determination of crystal structure at 3.1 angstrom resolution.
- Crystallographic soaking experiments with maltotriose.
Main Results:
- The maltoporin structure reveals an 18-stranded antiparallel beta-barrel.
- Inwardly folded loops create a constriction within the channel.
- Six aromatic residues line the channel, forming a hydrophobic translocation path.
- Maltotriose binding was observed along this path at the constriction site.
Conclusions:
- The E. coli maltoporin structure provides a detailed framework for porin-mediated transport.
- Aromatic residues and channel constriction are critical for guided diffusion of maltodextrins.
- This mechanism suggests how maltose and linear oligosaccharides cross the bacterial outer membrane.