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Going Forward Laterally: Transmembrane Passage of Hydrophobic Molecules through Protein Channel Walls
Author(s) -
van den Berg Bert
Publication year - 2010
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.201000105
Subject(s) - barrel (horology) , chemistry , biophysics , bacterial outer membrane , lipid bilayer , membrane , transmembrane protein , bilayer , molecule , phospholipid , hydrophobic effect , biochemistry , escherichia coli , materials science , organic chemistry , biology , receptor , composite material , gene
Regular phospholipid bilayers do not pose efficient barriers for the transport of hydrophobic molecules. The outer membrane (OM) surrounding Gram‐negative bacteria is a nontypical, asymmetric bilayer with an outer layer of lipopolysaccharide (LPS). The sugar molecules of the LPS layer prevent spontaneous diffusion of hydrophobic molecules across the OM. As regular OM channels such as porins do not allow passage of hydrophobic molecules, specialized OM transport proteins are required for their uptake. Such proteins, exemplified by channels of the FadL family, transport their substrates according to a lateral diffusion mechanism. Here, substrates diffuse from the lumen of the β‐barrel laterally into the OM, through a stable opening in the wall of the barrel. In this way, the lipopolysaccharide barrier is bypassed and, by depositing the substrates into the OM, a driving force for uptake is provided. Lateral diffusion through protein channel walls also occurs in α‐helical inner membrane proteins, and could represent a widespread mechanism for proteins that transport and interact with hydrophobic substrates.