Group of Prof. Dr.
coworkers: Melanie Surma, PD Dr. Winfried Hausner
is a hyperthermophilic archaeon that is able to utilize carbohydrates
like maltose, trehalose, and maltodextrins as carbon and energy source
(Fiala & Stetter, 1986). The uptake of these substrates is mediated
by binding protein dependent ABC-transporters which consist of three
different kinds of proteins: two permeases, that form the translocation
pore, two ATPase domains, that provide energy for the translocation
by hydrolysis of ATP, and a binding protein with high affiniy to its
substrate (Konig et al., 2002).
The genes encoding the different transport proteins are clustered in an operon and their expression is regulated together. They are induced only in the presence of specific substrates, i.e. maltose and trehalose for the maltose/trehalose transporter, and maltodextrins for the maltodextrin transporter.
In both cases the expression of the transport proteins is controlled by the regulator TrmB (transcriptional factor of the mal operon; Lee et al. 2005). TrmB is a repressor of transcription. In the absence of appropriate substrates it binds to the promoter region of the respective gene complex and thus inhibits transcription. In the presence of an inducer, however, causes a conformational change in the repressor, it looses contact of the promoter and transcription can take place again.
TrmB has a unique
characteristic: it recognizes different DNA-sequences on different promoters,
takes up different conformations upon binding to them, and thus recognizes
different inducers for different promoters. So TrmB shows a different
sugar specificity that depends on the nucleotide sequence of the TrmB
binding site (Figure 2). As a consequence one and the same sugar can
act as an inducer or as an anti-inducer, depending on the promoter TrmB
is bound to.
Besides TrmB three other TrmB orthologues have been found in Pyrococcus furiosus, called TrmBL1, TrmBL2, and TrmBL3. These are also repressors of transcription and are involved in the regulation of glycolytic genes. In vitro transcription assays showed that TrmB also recognizes the target promoters of TrmBL1-3, and vice versa. This leads to the conclusion that the sugar metabolism in Pyrococcus furiosus is controlled by a cross regulatory network of homologue repressor proteins. Furthermore, recent experiments using gluconeogenesis genes indicate that TrmBL1 does not act as an repressor or these promoters, but as an activator.