This family includes the well characterized maltoporins of Escherichia coli and Salmonella typhimurium as well as the sucrose-specific porin of Salmonella typhimurium, whose 3D structures have been resolved by X-ray diffraction. These porins form trimers but, in contrast to proteins belonging to other bacterial porin families which consist of 16 beta-stranded ß-barrels, they consist of an 18 beta-stranded ß-barrel. Despite the wider barrel compared to other porins, sugar-specific porins exhibit a narrower channel, showing only a small fraction of the ionic conductance of the latter porins. There is also evidence that in most cases, the N-terminal residues form a coiled-coil of alpha helices facilitating low-affinity sugar binding and supramolecular stabilisation.

Representative image: