Crystal structure of the photosensory module from a PAS-less cyanobacterial phytochrome as Pr shows a mix of dark-adapted and photoactivated features.

Phytochromes (Phys) are a diverse collection of photoreceptors that regulate numerous physiological and developmental processes in microorganisms and plants through photointerconversion between red-light-absorbing Pr and far-red light-absorbing Pfr states. Light is detected by an N-terminal photo-sensing module (PSM) sequentially comprised of Period/ARNT/Sim (PAS), cGMP-phosphodiesterase/adenylyl cyclase/FhlA (GAF), and Phy-specific (PHY) domains, with the bilin chromophore covalently-bound within the GAF domain. Phys sense light via the Pr/Pfr ratio measured by the light-induced rotation of the bilin D-pyrrole ring that triggers conformational changes within the PSM, which for microbial Phys reaches into an output region. A key step is a ß-stranded to α-helical reconfiguration of a hairpin loop extending from the PHY domain to contact the GAF domain. Besides canonical Phys, cyanobacteria express several variants, including a PAS-less subfamily that harbors just the GAF and PHY domains for light detection. Prior 2D-NMR studies of a model PAS-less Phy from Synechococcus_sp._JA-2-3B'a(2-13) (SyB-Cph1) proposed a unique photoconversion mechanism involving an A-pyrrole ring rotation while magic-angle-spinning NMR probing the chromophore proposed the prototypic D-ring flip. To help solve this conundrum, we determined the crystallographic structure of the GAF-PHY region from SyB-Cph1 as Pr. Surprisingly, this structure differs from canonical Phys by having a Pr ZZZsyn,syn,anti bilin configuration but shifted to the activated position in the binding pocket with consequent folding of the hairpin loop to α-helical, an architecture common for Pfr. Collectively, the PSM of SyB-Cph1 as Pr displayed a mix of dark-adapted and photoactivated features whose co-planar A-C pyrrole rings support a D-ring flip mechanism.

Antimicrobial Activity of Bark from Four North American Tree Species.

INTRODUCTION: Although many backcountry first aid kits contain antibiotic ointment, the supply can be quickly exhausted if a patient has extensive wounds or if there are multiple patients. METHODS: We assessed the antibacterial properties of bark extract from four North American woody plant species known to native Missourians as medicinal plants (Quercus macrocarpa, Salix humilis, Pinus echinata, and Hamamelis vernalis). We tested their antimicrobial properties, with the disc diffusion technique, against four common pathogenic bacterial species: Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterobacter aerogenes (now known as Klebsiella aerogenes). RESULTS: We report evidence of antibacterial activity of bark extract from all four plant species. CONCLUSIONS: Our results confirm that traditional uses of these species may be useful in fighting infection and could be especially useful in a wilderness setting when modern antibiotics are exhausted.