Solution Structure and Backbone Dynamics of the Pleckstrin Homology Domain of the Human Protein Kinase B (PKB/Akt). Interaction with Inositol Phosphates

The programmed cell death occurs as part of normal mammalian development. The induction of developmental cell death is a highly regulated process and can be suppressed by a variety of extracellular stimuli. Recently, the ability of trophic factors to promote survival have been attributed, at least in part, to the phosphatidylinositide 3'-OH kinase (PI3K)/Protein Kinase B (PKB, also named Akt) cascade. Several targets of the PI3K/PKB signaling pathway have been identified that may underlie the ability of this regulatory cascade to promote cell survival. PKB possesses a N-terminal Pleckstrin Homology (PH) domain that binds specifically and with high affinity to PtIns(3,4,5)P(3) and PtIns(3,4)P(2), the PI3K second messengers. PKB is then recruited to the plasma membrane by virtue of its interaction with 3'-OH phosphatidylinositides and activated. Recent evidence indicates that PKB is active in various types of human cancer; constitutive PKB signaling activation is believed to promote proliferation and increased cell survival, thereby contributing to cancer progression. Thus, it has been shown that induction of PKB activity is augmented by the TCL1/MTCP1 oncoproteins through a physical association requiring the PKB PH domain. Here we present the three-dimensional solution structure of the PH domain of the human protein PKB (isoform beta). PKBbeta-PH is an electrostatically polarized molecule that adopts the same fold and topology as other PH-domains, consisting of a beta-sandwich of seven strands capped on one top by an alpha-helix. The opposite face presents three variable loops that appear poorly defined in the NMR structure. Measurements of (15)N spin relaxation times and heteronuclear (15)N[(1)H]NOEs showed that this poor definition is due to intrinsic flexibility, involving complex motions on different time scales. Chemical shift mapping studies correctly defined the binding site of Ins(1,3,4,5)P(4) (the head group of PtIns(3,4,5)P(3)), as was previously proposed from a crystallographic study. More interestingly, these studies allowed us to define a putative alternative low-affinity binding site for Ins(1,4,5)P(3). The binding of this sugar to PKBbeta-PH might also involve non-specific association that could explain the stabilization of the protein in solution in the presence of Ins(1,4,5)P(3).     

Crystallization and preliminary X-ray crystallographic analysis of Plasmodium falciparum S-adenosyl-L-homocysteine hydrolase

S-adenosyl-l-homocysteine hydrolase from a malaria parasite Plasmodium falciparum (PfSAHH) has been crystallized by the vapor diffusion method. The crystals belong to an orthorhombic space group P212121 with the cell dimensions of a = 76.66 A, b = 86.31 A, and c = 335.6 A. There are four subunits (one tetramer) per asymmetric unit. X-ray diffraction data have been collected up to 2.8 A resolution. Self-rotation function studies suggest that the tetrameric PfSAHH molecule has the 222 point group symmetry.     

Blood-brain barrier disruption in the hypothalamus of young adult spontaneously hypertensive rats

Vascular permeability and endothelial glycocalyx were examined in young adult spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP), and Wistar Kyoto rats (WKY) as a control, in order to determine earlier changes in the blood-brain barrier (BBB) in the hypothalamus in chronic hypertension. These rats were injected with horseradish peroxidase (HRP) as an indicator of vascular permeability. Brain slices were developed with a chromogen and further examined with cationized ferritin, a marker for evaluating glycocalyx. Staining for HRP was seen around vessels in the hypothalamus of SHR and SHRSP, but was scarce in WKY. The reaction product of HRP appeared in the abluminal pits of endothelial cells and within the basal lamina of arterioles, showing increased vascular permeability in the hypothalamus of SHR and SHRSP, whereas there were no leaky vessels in the frontal cortex of SHR and SHRSP, or in both areas of WKY. The number of cationized ferritin particles binding to the capillary endothelial cells was decreased in the hypothalamus of SHR and SHRSP, while the number decreased in the frontal cortex of SHRSP, compared with those in WKY. Cationized ferritin binding was preserved in some leaky arterioles, while it was scarce or disappeared in other leaky vessels. These findings suggest that BBB disruption occurs in the hypothalamus of 3-month-old SHR and SHRSP, and that endothelial glycocalyx is markedly damaged there without a close relationship to the early changes in the BBB.     

Methotrexate enhances prostaglandin D2-stimulated heat shock protein 27 induction in osteoblasts

As for the pathogenesis of rheumatoid arthritis (RA), prostaglandins (PGs) act as important mediators of inflammation and joint destruction. Among them, PGD2 is well recognized as a potent regulator of osteoblastic functions. We previously showed that PGD2 stimulates the induction of heat shock protein 27 (HSP27) via protein kinase C (PKC)-dependent p38 mitogen-activated protein (MAP) kinase and p44/p42 MAP kinase in osteoblast-like MC3T3-E1 cells. Therefore, it is a current topic to clarify how HSP27 plays a role for regulating osteoblastic functions in the lesion of RA. On the other hand, methotrexate (MTX) is one of the most effective medicines for the treatment of RA. Here, we examined the effect of MTX on PGD2-stimulated HSP27 induction in MC3T3-E1 cells. The cells were pretreated with various doses of MTX including therapeutic dosage for RA, and then stimulated by PGD2. MTX significantly enhanced the PGD2- increased levels of HSP27 in a dose-dependent manner, although MTX alone had no effect on the levels of HSP27. In addition, MTX amplified the PGD2-increased levels of HSP27 mRNA. On the contrary, MTX had little effect on PGD2-induced formation of inositol phosphates, PKC activation and phosphorylations of MAP kinases. Our results strongly suggest that MTX enhances PGD2-stimulated HSP27 induction at a point downstream from MAP kinases in osteoblasts.     

Aroma sensing and indoor air monitoring by quartz crystal resonators with sensory films prepared by sputtering of biomaterials and sintered polymers

Thickness shear mode quartz-crystal resonator coated with plasma polymer films (PPFs) produced by radio-frequency sputtering of biomaterials and synthetic polymers were examined with respect to their abilities to continuously monitor indoor air. We confirmed the sensory capabilities of an array of PPF sensors to aromas emitted from essential oils at concentrations as low as the detection threshold of human olfaction. Changes in humidity induced a drift in the response curves of PPF sensors. On the contrary, volatile compounds exhibited pulse signals. The pulse signals of a D-phenylalanine sensor and a polyethylene sensor were synchronous, but the direction of the peaks was inverted in most cases. Compared with a photo-ionization detector sensor, the PPF sensors were able to detect subtle changes in the concentrations of volatile compounds in indoor air.     

A specific receptor site for glycerol, a new sweet tastant for Drosophila: structure-taste relationship of glycerol in the labellar sugar receptor cell

Glycerol, a linear triol, is a sweet tastant for mammals but it has not previously been recognized to stimulate the sense of taste in insects. Here we show by electrophysiological experimentation that it effectively stimulates the labellar sugar receptor cell of Drosophila. We also show that in accord with the electrophysiological observations, the behavioral feeding response to glycerol is dose dependent. 3-Amino-1,2-propanediol inhibited the response of the sugar receptor cell to glycerol, specifically and competitively, while it had almost no effect on responses to sucrose, D-glucose, D-fructose and trehalose. In the null Drosophila mutant for the trehalose receptor (DeltaEP19), the response to glycerol showed no change, in sharp contrast with a characteristic drastic decrease in the response to trehalose. The glycerol concentration-response curves for I-type and L-type labellar hairs were statistically indistinguishable, while those for sucrose, D-glucose, D-fructose and trehalose were clearly different. These all indicate the presence of a specific receptor site for glycerol. The glycerol site was characterized by comparing the effectiveness of various derivatives of glycerol. Based on this structure-taste relationship of glycerol, a model is proposed for the glycerol site including three subsites and two steric barriers, which cannot accommodate carbon-ring containing sugars such as D-glucose.     

Baby-transfer and other interactions between its mother and grandmother in a captive social group of lowland gorillas

This report describes the responses of an experienced gorilla mother to inappropriate maternal behavior displayed by her young adult daughter toward a newborn baby and repeated acts of baby-transfer between these two females in a captive social group of lowland gorillas (Gorilla g. gorilla). The quality of infant care by the young adult daughter clearly improved during the first 4 days after birth, and this improvement was at least partly based on her mothers encouragement. Thus, the mothers activities can be considered scaffolding for her daughter with regard to maternal infant care.