Partitioning-defective protein 6 (Par-6) activates atypical protein kinase C (aPKC) by pseudosubstrate displacement

Atypical protein kinase C (aPKC) controls cell polarity by modulating substrate cortical localization. Aberrant aPKC activity disrupts polarity, yet the mechanisms that control aPKC remain poorly understood. We used a reconstituted system with purified components and a cultured cell cortical displacement assay to investigate aPKC regulation. We find that aPKC is autoinhibited by two domains within its NH(2)-terminal regulatory half, a pseudosubstrate motif that occupies the kinase active site, and a C1 domain that assists in this process. The Par complex member Par-6, previously thought to inhibit aPKC, is a potent activator of aPKC in our assays. Par-6 and aPKC interact via PB1 domain heterodimerization, and this interaction activates aPKC by displacing the pseudosubstrate, although full activity requires the Par-6 CRIB-PDZ domains. We propose that, along with its previously described roles in controlling aPKC localization, Par-6 allosterically activates aPKC to allow for high spatial and temporal control of substrate phosphorylation and polarization.     

Effects of hydrological forcing on the structure of a tropical estuarine food web

River flow can impact which sources of particulate organic matter (POM) fuel estuarine food webs. Here, we used stable carbon (C) and nitrogen (N) isotope analyses to compare how contributions of different POM sources (terrestrial, estuarine, and marine) to the diets of zooplankton and juvenile fishes differed between low and high river flow conditions, as well as spatially across a tropical estuary, Hilo Bay, Hawaii, USA. Diets of zooplankton and juvenile fishes were affected by river flow conditions, but the magnitude and the change in the basal resources depended on the location of the station in the estuary relative to the ocean and the river mouths. Consumers from the station most isolated from the ocean and with groundwater and overland flow inputs, utilized a combination of estuarine and terrestrial POM during both low and high river flow conditions and exhibited less variability in their basal resources than stations with direct ocean exchange. Consumers from stations in the Bay most affected by ocean exchange and river inputs utilized a combination of estuarine, terrestrial, and marine POM during low flow conditions, but shifted to marine and terrestrial POM during high river flow conditions. This shift to using terrestrial POM during high river flow conditions was substantial and up to 40% higher than values measured in other estuaries. Factors suspected to be affecting which POM source(s) consumers use in Hilo Bay are gross primary production, biological availability of exported terrestrial OM, and estuarine bacteria biomass, all of which are affected by river flow. Overall, our results suggest that Hilo Bay's food web and possibly those from other tropical estuaries are vulnerable to changes in hydrology, which may be further enhanced by global climate change.     

Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer's disease transgenic mice.

Inhibition of neocortical beta-amyloid (Abeta) accumulation may be essential in an effective therapeutic intervention for Alzheimer's disease (AD). Cu and Zn are enriched in Abeta deposits in AD, which are solubilized by Cu/Zn-selective chelators in vitro. Here we report a 49% decrease in brain Abeta deposition (-375 microg/g wet weight, p = 0.0001) in a blinded study of APP2576 transgenic mice treated orally for 9 weeks with clioquinol, an antibiotic and bioavailable Cu/Zn chelator. This was accompanied by a modest increase in soluble Abeta (1.45% of total cerebral Abeta); APP, synaptophysin, and GFAP levels were unaffected. General health and body weight parameters were significantly more stable in the treated animals. These results support targeting the interactions of Cu and Zn with Abeta as a novel therapy for the prevention and treatment of AD.     

Magnification: gene amplification by an inducible system of sister chromatid exchange

Magnification, an increase in 18S + 28S ribosomal RNA genes, occurs in germ-line cells of rDNA-defecient Drosophila and resilts in a chromosomal change in rRNA gene number. Although differing hypotheses have been advanced, current evidence favors unequal sister chromatid exchange as the basis of this system of gene amplification. Genetic studies implicate repair activities in the process of magnification.     

Catalysis by imidazolium ion and metal ions in the reaction of a phosphate diester

The rates of reaction of catechol cyclic phosphate in water and in acetonitrile-water demonstrate that imidazolium ion and metal ions (Na⁺, Mg²⁺, Zn²⁺) cause significant accelerations. These studies provide models for the potential role of cations in catalysis of reactions of phosphate anions by enzymes. In catalysis by Zn²⁺, we find that two to three imidazoles are required for coordination to Zn²⁺ for most effective catalysis. Enough water must be present to solvate imidazole and coordinate to Zn²⁺, indicating that a coordinated H₂O is the nucleophile in Zn²⁺ catalysis. Product analysis also supports this conclusion.