Structural analysis of the substrate recognition mechanism in O-phosphoserine sulfhydrylase from the hyperthermophilic archaeon Aeropyrum pernix K1

L-Cysteine is synthesized from O-acetyl-L-serine (OAS) and sulfide by O-acetylserine sulfhydrylase (OASS; EC 2.5.1.47) in plants and bacteria. O-phosphoserine sulfhydrylase (OPSS; EC 2.5.1.65) is a novel enzyme from the hyperthermophilic aerobic archaeon Aeropyrum pernix K1 (2003). OPSS can use OAS or O-phospho-L-serine (OPS) to synthesize L-cysteine. To elucidate the mechanism of the substrate specificity of OPSS, we analyzed three-dimensional structures of the active site of the enzyme. The active-site lysine (K127) of OPSS forms an internal Schiff base with pyridoxal 5'-phosphate. Therefore, crystals of the complexes formed by the K127A mutant with the external Schiff base of pyridoxal 5'-phosphate with either OPS or OAS were prepared and examined by X-ray diffraction analysis. In contrast to that observed for OASS, no significant difference was seen in the overall structure between the free and complexed forms of OPSS. The side chains of T152, S153, and Q224 interacted with the carboxylate of the substrates, as a previous study has suggested. The side chain of R297 has been proposed to recognize the phosphate group of OPS. Surprisingly, however, the position of R297 was significantly unchanged in the complex of the OPSS K127A mutant with the external Schiff base, allowing enough space for an interaction with OPS. The positively charged environment around the entrance of the active site including S153 and R297 is important for accepting negatively charged substrates such as OPS.     

Artificial ladder-shaped polyethers that inhibit maitotoxin-induced Ca2+ influx in rat glioma C6 cells

Maitotoxin (MTX) is a ladder-shaped polyether produced by the epiphytic dinoflagellate Gambierdiscus toxicus. It is known to elicit potent toxicity against mammals and induce influx of Ca(2+) into cells. An artificial ladder-shaped polyether possessing a 6/7/6/6/7/6/6 heptacyclic ring system, which was designed for elucidating interactions with transmembrane proteins, was found to be the most potent inhibitor against MTX-induced Ca(2+) influx that has ever been reported.     

Effects of systemic sitafloxacin on periodontal infection control in elderly patients

doi: 10.1111/j.1741‐2358.2011.00605.x
Effects of systemic sitafloxacin on periodontal infection control in elderly patients Objective: To evaluate the microbiological and clinical effects of the systemic administration of sitafloxacin (STFX) on periodontal pockets in elderly patients receiving supportive periodontal therapy (SPT). Background: Periodontitis is a risk factor for atherosclerosis. Better periodontal health contributes to reduce atherosclerosis‐related diseases in elderly population. Materials and methods: Forty‐four patients undergoing SPT were randomly assigned to two groups: a test group took 100 mg/day of STFX for five consecutive days, or a control group received scaling and root planing (SRP) under local anaesthesia. Microbiological and clinical parameters were examined at baseline and at 1 and 3 months after therapy. Results: The presence of Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia was significantly reduced at 1 month after treatment in both groups. The median reductions of the bacteria between the baseline and 1 month were 3.08 and 2.54% in the STFX‐ and SRP‐treated groups, respectively. Both treatments significantly decreased the probing depth at 1 and 3 months compared to the baseline. Conclusion: The systemic administration of STFX is effective at improving periodontal health during SPT and could be an alternative to SRP for elderly patients who cannot undergo anaesthesia or are at risk of tissue injury.     

Catastrophic shifts in vertical distributions of phytoplankton The existence of a bifurcation set

A model of phytoplankton dynamics within a water column was analyzed with special consideration on the existence of a bifurcation set in the parameter space. We considered two resources, light and a limiting nutrient, for phytoplankton growth and assumed that the water column is separated into two layers by thermal and/or density stratification. It was shown that there exists a bifurcation set in the parameter space when the growth function meets several conditions that are general for growth functions of two essential resources. Specifically, these conditions include that a less abundant of the two resources limits the growth while the effect of the other is sufficiently small. Folded structure with two stable states separated by one unstable state appears in the catastrophe manifold when parameters move to a certain direction with a certain curvature from a point in the bifurcation set. These results suggest that occurrence of discontinuous transition between two alternative vertical patterns is possible nature of phytoplankton dynamics within a stratified water column.     

Coagulation of soy proteins induced by thermolysin and comparison of the coagulation reaction with that induced by subtilisin Carlsberg

It is known that coagula are formed when soy proteins are treated by subtilisin Carlsberg. Time-course of the coagulation can be monitored by measuring the turbidity (OD₆₆₀) of soy protein isolates (SPI) solution [Inouye K, Nagai K, Takita T. Coagulation of soy protein isolates induced by subtilisin Carlsberg. J Agric Food Chem 2002;50:1237–42]. In this study, we examined the coagulation of the digests produced in the digestion of SPI with thermolysin. SPI treated at 80 °C coagulated by hydrolysis with either of thermolysin and subtilisin Carlsberg, but that treated at 37 °C did not. The velocities of the coagulation were almost the same between the digestions with thermolysin and subtilisin Carlsberg, while the amount of the coagula in the former was 50–80% of that in the latter. With increasing the thermolysin concentration from 0.1 to 5 μM, the velocity of the coagulation increased while the amount of the coagula was constant. With increasing the reaction temperature from 37 to 70 °C, the velocity increased while the amount decreased. The digests from 11S soy proteins coagulated drastically compared to those from either of SPI, 7S soy proteins, and the mixture of 7S and 11S soy proteins (1:2 for w/v), suggesting that the coagulation of the digests from 11S soy proteins might be suppressed by those from 7S soy proteins.     

Optical coherence tomography for dynamic investigation of mammalian reproductive processes

The biological events associated with mammalian reproductive processes are highly dynamic and tightly regulated by molecular, genetic, and biomechanical factors. Implementation of live imaging in reproductive research is vital for the advancement of our understanding of normal reproductive physiology and for improving the management of reproductive disorders. Optical coherence tomography (OCT) is emerging as a promising tool for dynamic volumetric imaging of various reproductive processes in mice and other animal models. In this review, we summarize recent studies employing OCT-based approaches toward the investigation of reproductive processes in both, males and females. We describe how OCT can be applied to study structural features of the male reproductive system and sperm transport through the male reproductive tract. We review OCT applications for in vitro and dynamic in vivo imaging of the female reproductive system, staging and tracking of oocytes and embryos, and investigations of the oocyte/embryo transport through the oviduct. We describe how the functional OCT approach can be applied to the analysis of cilia dynamics within the male and female reproductive systems. We also discuss the areas of research, where OCT could find potential applications to progress our understanding of normal reproductive physiology and reproductive disorders.     

Identification of an internal cavity in the PhoQ sensor domain for PhoQ activity and SafA-mediated control

The PhoQ/PhoP two-component signal transduction system is conserved in various Gram-negative bacteria and is often involved in the expression of virulence in pathogens. The small inner membrane protein SafA activates PhoQ in Escherichia coli independently from other known signals that control PhoQ activity. We have previously shown that SafA directly interacts with the sensor domain of the periplasmic region of PhoQ (PhoQ-SD) for activation, and that a D179R mutation in PhoQ-SD attenuates PhoQ activation by SafA. In this study, structural comparison of wild-type PhoQ-SD and D179R revealed a difference in the cavity (SD (sensory domain) pocket) found in the central core of this domain. This was the only structural difference between the two proteins. Site-directed mutagenesis of the residues surrounding the SD pocket has supported the SD pocket as a site involved in PhoQ activity. Furthermore, the SD pocket has also been shown to be involved in SafA-mediated PhoQ control.