18 research outputs found
New insights into the photochemistry of carotenoid spheroidenone in light-harvesting complex 2 from the purple bacterium Rhodobacter sphaeroides
Light-harvesting complex 2 (LH2) from the
semi-aerobically grown purple phototrophic bacterium
Rhodobacter sphaeroides was studied using optical (static
and time-resolved) and resonance Raman spectroscopies.
This antenna complex comprises bacteriochlorophyll
(BChl) a and the carotenoid spheroidenone, a ketolated
derivative of spheroidene. The results indicate that the
spheroidenone-LH2 complex contains two spectral forms
of the carotenoid: (1) a minor, ââblueââ form with an S2
(11
Bu
?) spectral origin band at 522 nm, shifted from the
position in organic media simply by the high polarizability
of the binding site, and (2) the major, ââredââ form with the
origin band at 562 nm that is associated with a pool of
pigments that more strongly interact with protein residues,
most likely via hydrogen bonding. Application of targeted
modeling of excited-state decay pathways after carotenoid
excitation suggests that the high (92%) carotenoid-to-BChl
energy transfer efficiency in this LH2 system, relative to
LH2 complexes binding carotenoids with comparable
double-bond conjugation lengths, derives mainly from
resonance energy transfer from spheroidenone S2 (11
Bu
?)
state to BChl a via the Qx state of the latter, accounting for
60% of the total transfer. The elevated S2 (11
Bu
?) ? Qx
transfer efficiency is apparently associated with substantially
decreased energy gap (increased spectral overlap)
between the virtual S2 (11
Bu
?) ? S0 (11
Ag
-) carotenoid
emission and Qx absorption of BChl a. This reduced
energetic gap is the ultimate consequence of strong carotenoidâprotein
interactions, including the inferred hydrogen
bondin
Regulatory (pan-)genome of an obligate intracellular pathogen in the PVC superphylum.
Like other obligate intracellular bacteria, the Chlamydiae feature a compact regulatory genome that remains uncharted owing to poor genetic tractability. Exploiting the reduced number of transcription factors (TFs) encoded in the chlamydial (pan-)genome as a model for TF control supporting the intracellular lifestyle, we determined the conserved landscape of TF specificities by ChIP-Seq (chromatin immunoprecipitation-sequencing) in the chlamydial pathogen Waddlia chondrophila. Among 10 conserved TFs, Euo emerged as a master TF targeting >100 promoters through conserved residues in a DNA excisionase-like winged helix-turn-helix-like (wHTH) fold. Minimal target (Euo) boxes were found in conserved developmentally-regulated genes governing vertical genome transmission (cytokinesis and DNA replication) and genome plasticity (transposases). Our ChIP-Seq analysis with intracellular bacteria not only reveals that global TF regulation is maintained in the reduced regulatory genomes of Chlamydiae, but also predicts that master TFs interpret genomic information in the obligate intracellular α-proteobacteria, including the rickettsiae, from which modern day mitochondria evolved
Solubility and stability of melatonin in propylene glycol and 2-hydroxypropyl-ÎČ-cyclodextrin vehicles
Application of fluorescent in situ hybridisation for demonstration of Coxiella burnetti in placentas from ruminant abortions
Intraflagellar Transport and Functional Analysis of Genes Required for Flagellum Formation in Trypanosomes
Intraflagellar transport (IFT) is the bidirectional movement of protein complexes required for cilia and flagella formation. We investigated IFT by analyzing nine conventional IFT genes and five novel putative IFT genes (PIFT) in Trypanosoma brucei that maintain its existing flagellum while assembling a new flagellum. Immunostaining against IFT172 or expression of tagged IFT20 or green fluorescent protein GFP::IFT52 revealed the presence of IFT proteins along the axoneme and at the basal body and probasal body regions of both old and new flagella. IFT particles were detected by electron microscopy and exhibited a strict localization to axonemal microtubules 3â4 and 7â8, suggesting the existence of specific IFT tracks. Rapid (>3 ÎŒm/s) bidirectional intraflagellar movement of GFP::IFT52 was observed in old and new flagella. RNA interference silencing demonstrated that all individual IFT and PIFT genes are essential for new flagellum construction but the old flagellum remained present. Inhibition of IFTB proteins completely blocked axoneme construction. Absence of IFTA proteins (IFT122 and IFT140) led to formation of short flagella filled with IFT172, indicative of defects in retrograde transport. Two PIFT proteins turned out to be required for retrograde transport and three for anterograde transport. Finally, flagellum membrane elongation continues despite the absence of axonemal microtubules in all IFT/PIFT mutant