CymA of Klebsiella oxytoca, is a porin essential for growth on cyclodextrins, but it can also complement the deficiency of a LamB (maltoporin) mutant of Escherichia coli for growth on linear maltodextrins, indicating that both cyclic and linear oligosaccharides are accepted as substrates. This protein forms ion-permeable channels, which exhibit a substantial current noise. CymA-induced membrane conductance decreased considerably upon addition of alpha-cyclodextrin, whereas the affinity was lower for beta-cyclodextrin and even lower for gamma-cyclodextrin. Unlike most bacterial porins, cymA does not form trimeric complexes in lipid membranes and shows no tendency to trimerise in solution. However, it seems to form homotetramers with a central pore, and therefore lacks the typical trimeric structure of most porins. It is also speculated it be distantly related to OmpG. A recently published structure shows that members of this family have 14 TM segments.

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