Identifizierung eines Maltodextrintransporters in der äußeren Membran von Caulobacter crescentus (English shop)

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TonB-dependent membrane receptors in bacteria have so far been characterized for the uptake of iron and vitamin B12. The genome sequence of the Gram-negative bacterium Caulobacter crescentus predicts 65 TonB-dependent membrane receptors, which cannot all be responsible for the iron supply. In this work, an attempt was made to identify a membrane protein in C. crescentus to which a transport function for substrates other than iron can be assigned.

After cultivation of C. crescentus in various media, two-dimensional gel electrophoresis made it possible to identify a protein in the outer membrane whose expression was induced by maltose. MALDI-TOF analyses of the protein, designated MalA, indicated that it should be a TonB-dependent protein whose function has not been described in detail so far.

For the characterization of MalA, a chromosomal malA deletion mutant was generated in C. crescentus. The growth behaviour of this mutant with maltodextrins as the sole carbon source demonstrated that MalA is responsible for the uptake of maltodextrins. Smaller maltodextrins such as maltose, maltotriose and maltotetraose can still enter the cell by diffusion through simple porins, whereas the larger maltodextrins such as maltopentaose and maltohexaose are taken up in a MalA-dependent manner.
Furthermore, it could be shown that maltodextrin uptake occurs in an ExbB- and ExbD-dependent manner.