Tetracycline-modifying enzyme SmTetX from Stenotrophomonas maltophilia.

The resistance of the emerging human pathogen Stenotrophomonas maltophilia to tetracycline antibiotics mainly depends on multidrug efflux pumps and ribosomal protection enzymes. However, the genomes of several strains of this Gram-negative bacterium code for a FAD-dependent monooxygenase (SmTetX) homologous to tetracycline destructases. This protein was recombinantly produced and its structure and function were investigated. Activity assays using SmTetX showed its ability to modify oxytetracycline with a catalytic rate comparable to those of other destructases. SmTetX shares its fold with the tetracycline destructase TetX from Bacteroides thetaiotaomicron; however, its active site possesses an aromatic region that is unique in this enzyme family. A docking study confirmed tetracycline and its analogues to be the preferred binders amongst various classes of antibiotics.

A highly active S1-P1 nuclease from the opportunistic pathogen Stenotrophomonas maltophilia cleaves c-di-GMP.

A number of multidrug-resistant bacterial pathogens code for S1-P1 nucleases with a poorly understood role. We have characterized a recombinant form of S1-P1 nuclease from Stenotrophomonas maltophilia, an opportunistic pathogen. S. maltophilia nuclease 1 (SmNuc1) acts predominantly as an RNase and is active in a wide range of temperatures and pH. It retains a notable level of activity towards RNA and ssDNA at pH 5 and 9 and about 10% of activity towards RNA at 10 °C. SmNuc1 with very high catalytic rates outperforms S1 nuclease from Aspergillus oryzae and other similar nucleases on all types of substrates. SmNuc1 degrades second messenger c-di-GMP, which has potential implications for its role in the pathogenicity of S. maltophilia.

Atomic resolution studies of S1 nuclease complexes reveal details of RNA interaction with the enzyme despite multiple lattice-translocation defects.

S1 nuclease from Aspergillus oryzae is a single-strand-specific nuclease from the S1/P1 family that is utilized in biochemistry and biotechnology. S1 nuclease is active on both RNA and DNA but with differing catalytic efficiencies. This study clarifies its catalytic properties using a thorough comparison of differences in the binding of RNA and DNA in the active site of S1 nuclease based on X-ray structures, including two newly solved complexes of S1 nuclease with the products of RNA cleavage at atomic resolution. Conclusions derived from this comparison are valid for the whole S1/P1 nuclease family. For proper model building and refinement, multiple lattice-translocation defects present in the measured diffraction data needed to be solved. Two different approaches were tested and compared. Correction of the measured intensities proved to be superior to the use of the dislocation model of asymmetric units with partial occupancy of individual chains. As the crystals suffered from multiple lattice translocations, equations for their correction were derived de novo. The presented approach to the correction of multiple lattice-translocation defects may help to solve similar problems in the field of protein X-ray crystallography.

New species of Moluccan trichaline net-winged beetles, with remarks on the phylogenetic position and distribution of Schizotrichalus (Coleoptera: Lycidae: Metriorrhynchinae).

The Moluccan net-winged beetle fauna remains poorly studied and here, new species of Schizotrichalus Kleine, 1926 and Eniclases Waterhouse, 1879 are reported from Halmahera. Using morphological traits and cox1 mitochondrial DNA sequences, we propose two new species, Eniclases kusyi sp. nov. and Schizotrichalus halmaherensis sp. nov., and redescribe E. moluccanus Kleine, 1930. New molecular data confirm morphology-based sister relationships between Schizotrichalus and Eniclases and the analysis identifies the combined area of the present-day Halmahera and New Guinea as an ancestral area of these genera. Now, Halmahera and New Guinea are quite similar in respect of the number of trichaline genera. Concerning the size of islands and the recent origin of the nowadays northern Moluccas, these results are unexpected and thus the general validity of this distribution pattern should be confirmed with other groups of beetles.