Circuit architecture explains functional similarity of bacterial heat shock responses

Heat shock response is a stress response to temperature changes and a consecutive increase in amounts of unfolded proteins. To restore homeostasis, cells upregulate chaperones facilitating protein folding by means of transcription factors (TF). We here investigate two heat shock systems: one characteristic to gram negative bacteria, mediated by transcriptional activator sigma32 in E. coli, and another characteristic to gram positive bacteria, mediated by transcriptional repressor HrcA in L. lactis. We construct simple mathematical model of the two systems focusing on the negative feedbacks, where free chaperons suppress sigma32 activation in the former, while they activate HrcA repression in the latter. We demonstrate that both systems, in spite of the difference at the TF regulation level, are capable of showing very similar heat shock dynamics. We find that differences in regulation impose distinct constrains on chaperone-TF binding affinities: the binding constant of free sigma32 to chaperon DnaK, known to be in 100 nM range, set the lower limit of amount of free chaperon that the system can sense the change at the heat shock, while the binding affinity of HrcA to chaperon GroE set the upper limit and have to be rather large extending into the micromolar range.Comment: 17 pages, 5 figure

A Bacillus megaterium plasmid system for the production, export, and one-step purification of affinity-tagged heterologous levansucrase from growth medium

A multiple vector system for the production and export of recombinant affinity-tagged proteins in Bacillus megaterium was developed. Up to 1 mg/liter of a His(6)-tagged or Strep-tagged Lactobacillus reuteri levansucrase was directed into the growth medium, using the B. megaterium esterase LipA signal peptide, and recovered by one-step affinity chromatography

Alkynyl-functionalized gold NHC complexes and their coinage metal clusters

Phenylpropynyl-functionalized imidazolium salts, as well as their gold complexes, were prepared in excellent yields affording suitable starting materials for metal cluster synthesis. The reactions of these gold complexes with coinage metal phenylacetylides [M(CCPh)]x (M = Cu, Ag) resulted in the formation of novel heterometallic hexanuclear clusters which exhibit mixed metallophillic interactions and intense white photoluminescence at low temperature