Crystallization and preliminary X-ray characterization of a PaaX-like protein from Sulfolobus solfataricus P2

Microbial degradation of aromatic compounds - from one strategy to four

Aromatic compounds are both common growth substrates for microorganisms and prominent environmental pollutants. The crucial step in their degradation is overcoming the resonance energy that stabilizes the ring structure. The classical strategy for degradation comprises an attack by oxygenases that hydroxylate and finally cleave the ring with the help of activated molecular oxygen. Here, we describe three alternative strategies used by microorganisms to degrade aromatic compounds. All three of these methods involve the use of CoA thioesters and ring cleavage by hydrolysis. However, these strategies are based on different ring activation mechanisms that consist of either formation of a non-aromatic ring-epoxide under oxic conditions, or reduction of the aromatic ring under anoxic conditions using one of two completely different systems.

Crystallization and preliminary X-ray diffraction studies of the transcriptional repressor PaaX, the main regulator of the phenylacetic acid degradation pathway in Escherichia coli W

PaaX is the main regulator of the phenylacetic acid aerobic degradation pathway in bacteria and acts as a transcriptional repressor in the absence of its inducer phenylacetyl-coenzyme A. The natural presence and the recent accumulation of a variety of highly toxic aromatic compounds owing to human pollution has created considerable interest in the study of degradation pathways in bacteria, the most important microorganisms capable of recycling these compounds, in order to design and apply novel bioremediation strategies. PaaX from Escherichia coli W was cloned, overexpressed, purified and crystallized using the sitting-drop vapour-diffusion method at 291 K. Crystals grew from a mixture of 0.9 M Li(2)SO(4) and 0.5 M sodium citrate pH 5.8. These crystals, which belonged to the monoclinic space group C2 with unit-cell parameters a = 167.88, b = 106.23, c = 85.87 Å, β = 108.33°, allowed the collection of an X-ray data set to 2.3 Å resolution.