Non-ribosomal peptide synthetases constitute a class of modular multi-domain enzymes found in the cytoplasm of bacteria and fungi that synthesize a large variety of highly diverse peptides. Many of these peptides have been used as antibiotics, anti-inflammatory, anti-tumor or immunosuppressive drugs, making the investigation of the structure and function of NRPS and the related polyketide synthetase (PKS) systems of high medical relevance. NRPS systems are organized in multi-subunit clusters and each subunit in turn is composed of modules, capable of carrying out one cycle of chain elongation. A typical module consists of an adenylation (A) domain, a peptidyl carrier protein (PCP) domain and a condensation(C) domain. A domains (~550 residues) and C domains (~450 residues) are responsible for loading PCP domains with the cognate amino acid and catalyzing the peptide bond formation between the upstream aminoacyl or peptidyl PCP and downstream peptidyl PCP, respectively. During the entire process, the growing peptide chain is covalently linked to a phosphopantetheine cofactor which itself is attached to a conserved serine by a dedicated Ppan transferase (Pptase). As an example the organization of the surfactin synthetase is shown below.
The modular design of NRPS assembly lines combined with the use of many of their products as antibiotics, anti-cancer or anit-inflammatory drugs has sparked hopes that new and potentially medically relevant peptides could be obtained by designing new assembly lines from the individual modules of naturally occurring NRPS systems. These attempts, however, so far have demonstrated that even small changes in the assembly lines lead to considerable reductions in product yield. One interpretation of these failures to design a new assembly line is that the individual domains are not merely beads on string which only pass the intermediates to different reaction centers, but rather that there must be specific inter domain or even inter subunit contacts within these huge clusters which are vital to the completion of the final products. We are investigating the interaction between the different components of several NRPS systems. In particular, we have found that the PCP domains adopt several conformations that are importnat for selecting the interaction partners. Currently, we are focusing on structural investigaton of teh interaction of PCPs with several other domains.
- Koglin, A., Mofid. M. R., Löhr, F., Schäfer. B., Rogov, V. V. , Blum, M. M., Mittag, T., Marahiel, M.A., Bernhard, F.& Dötsch, V. Conformational switches modulate protein interactions in peptide antibiotic synthetases. Science 312, 273–276 (2006)
- Koglin, A., Löhr, F., Bernhard, F., Rogov, V. R., Frueh, D. P., Strieter, E. R., Mofid, M. R., Güntert, P., Wagner, G., Walsh, C. T., Marahiel, M. A. & Dötsch, V. Structural basis for the selectivity of the external thioesterase of the surfactin synthetase. Nature 454, 907–911 (2008)