Properties of transmembrane helix TM1 of the DcuS sensor kinase of Escherichia coli, the stator for TM2 piston signaling

The sensor kinase DcuS of Escherichia coli perceives extracellular fumarate by a periplasmic PAS_P sensor domain. Transmembrane (TM) helix TM2, present as TM2-TM2' homo-dimer, transmits fumarate activation in a piston-slide across the membrane. The second TM helix of DcuS, TM1, is known to lack piston movement. Structural and functional properties of TM1 were analyzed. Oxidative Cys-crosslinking (CL) revealed homo-dimerization of TM1 over the complete membrane, but only the central part showed α-helical +3/+4 spacing of the CL maxima. The GALLEX bacterial two-hybrid system indicates TM1/TM1' interaction, and the presence of a TM1-TM1' homo-dimer is suggested. The peripheral TM1 regions presented CL in a spacing atypical for α-helical arrangement. On the periplasmic side the deviation extended over 11 AA residues (V32-S42) between the α-helical part of TM1 and the onset of PAS_P. In the V32-S42 region, CL efficiency decreased in the presence of fumarate. Therefore, TM1 exists as a homo-dimer with α-helical arrangement in the central membrane region, and non-α-helical arrangement in the connector to PAS_P. The fumarate induced structural response in the V32-S42 region is suggested to represent a structural adaptation to the shift of TM2 in the TM1-TM1'/TM2-TM2' four-helical bundle.

Polar localization of a tripartite complex of the two-component system DcuS/DcuR and the transporter DctA in Escherichia coli depends on the sensor kinase DcuS

The C4-dicarboxylate responsive sensor kinase DcuS of the DcuS/DcuR two-component system of E. coli is membrane-bound and reveals a polar localization. DcuS uses the C4-dicarboxylate transporter DctA as a co-regulator forming DctA/DcuS sensor units. Here it is shown by fluorescence microscopy with fusion proteins that DcuS has a dynamic and preferential polar localization, even at very low expression levels. Single assemblies of DcuS had high mobility in fast time lapse acquisitions, and fast recovery in FRAP experiments, excluding polar accumulation due to aggregation. DctA and DcuR fused to derivatives of the YFP protein are dispersed in the membrane or in the cytosol, respectively, when expressed without DcuS, but co-localize with DcuS when co-expressed at appropriate levels. Thus, DcuS is required for location of DctA and DcuR at the poles and formation of tripartite DctA/DcuS/DcuR sensor/regulator complexes. Vice versa, DctA, DcuR and the alternative succinate transporter DauA were not essential for polar localization of DcuS, suggesting that the polar trapping occurs by DcuS. Cardiolipin, the high curvature at the cell poles, and the cytoskeletal protein MreB were not required for polar localization. In contrast, polar localization of DcuS required the presence of the cytoplasmic PAS(C) and the kinase domains of DcuS.

[Gardner's syndrome: report of a case]

Gardner's syndrome consists of multiple polyposis of the large intestine and soft and hard tissue tumors. The syndrome should be considered in case of supernumerary teeth, odontomas, osteoma and soft tissue tumors. These findings often precede colonic involvement. Careful attention should be directed towards the family history. The importance of this syndrome lies in the great tendency of the polyps to become malignant. Dentist and oral surgeon play an important role in the early detection of this syndrome and thus prevention of malignant degeneration of the intestinal polyps.

[Orbital cellulitis after a dental infection]

Blindness as a complication of a dental infection is rare. A nineteen-year-old male is presented with an apical abscess, leading to a maxillary sinusitis, orbital cellulitis and an imminent cavernous sinus thrombosis.