Evidence that nuclear receptors are related to terpene synthases

Ligand-activated nuclear receptors (NRs) orchestrate development, growth, and reproduction across all animal lifeforms – the Metazoa – but how NRs evolved remains mysterious. Given the NR ligands including steroids and retinoids are predominantly terpenoids, we asked whether NRs might have evolved from enzymes that catalyze terpene synthesis and metabolism. We provide evidence suggesting that NRs may be related to the terpene synthase (TS) enzyme superfamily. Based on over 10,000 3D structural comparisons, we report that the NR ligand-binding domain and TS enzymes share a conserved core of seven α-helical segments. In addition, the 3D locations of the major ligand-contacting residues are also conserved between the two protein classes. Primary sequence comparisons reveal suggestive similarities specifically between NRs and the subfamily of cis-isoprene transferases, notably with dehydrodolichyl pyrophosphate synthase and its obligate partner, NUS1/NOGOB receptor. Pharmacological overlaps between NRs and TS enzymes add weight to the contention that they share a distant evolutionary origin, and the combined data raise the possibility that a ligand-gated receptor may have arisen from an enzyme antecedent. However, our findings do not formally exclude other interpretations such as convergent evolution, and further analysis will be necessary to confirm the inferred relationship between the two protein classes

Loss of hippocampal serine protease BSP1/neuropsin predisposes to global seizure activity

Serine proteases in the adult CNS contribute both to activity-dependent structural changes accompanying learning and to the regulation of excitotoxic cell death. Brain serine protease 1 (BSP1)/neuropsin is a trypsin-like serine protease exclusively expressed, within the CNS, in the hippocampus and associated limbic structures. To explore the role of this enzyme, we have used gene targeting to disrupt this gene in mice. Mutant mice were viable and overtly normal; they displayed normal hippocampal long-term synaptic potentiation (LTP) and exhibited no deficits in spatial navigation (water maze). Nevertheless, electrophysiological studies revealed that the hippocampus of mice lacking this specifically expressed protease possessed an increased susceptibility for hyperexcitability (polyspiking) in response to repetitive afferent stimulation. Furthermore, seizure activity on kainic acid administration was markedly increased in mutant mice and was accompanied by heightened immediate early gene (c-fos) expression throughout the brain. In view of the regional selectivity of BSP1/neuropsin brain expression, the observed phenotype may selectively reflect limbic function, further implicating the hippocampus and amygdala in controlling cortical activation. Within the hippocampus, our data suggest that BSP1/neuropsin, unlike other serine proteases, has little effect on physiological synaptic remodeling and instead plays a role in limiting neuronal hyperexcitability induced by epileptogenic insult

Toward homochiral protocells in noncatalytic peptide systems

The activation-polymerization-epimerization-depolymerization (APED) model of Plasson et al. has recently been proposed as a mechanism for the evolution of homochirality on prebiotic Earth. The dynamics of the APED model in two-dimensional spatially-extended systems is investigated for various realistic reaction parameters. It is found that the APED system allows for the formation of isolated homochiral proto-domains surrounded by a racemate. A diffusive slowdown of the APED network such as induced through tidal motion or evaporating pools and lagoons leads to the stabilization of homochiral bounded structures as expected in the first self-assembled protocells.Comment: 10 pages, 5 figure

Melting and homogeneity in germanium-silicon alloys and a modified micro-manufactured assembly for stable high pressure and temperature measurements

We present a modified assembly for high pressure and temperature measurements in a MAX80 press. Thedesigns include a T-shaped power coupler with a ring-shaped insulator, a precision made, all-in-one singlepiececrucible, with mirror-image located, flat-bottomed sample and pressure marker chambers, with pressfitlids and thermocouple insert in the middle of the crucible. These features facilitate assembly stability,reproducibility of in situ measurements, avoidance of chemical contamination, portability of assemblyand ease of sectioning for further analysis. These attributes are important in evaluating phase relations athigh pressure, especially where melting of the charge is investigated. While the cubic-diamond structuredsilicon–germanium system exhibits a complete solid solution, in practice, homogeneous solid solutionsare not readily accessible because of the considerable difference in temperature between the liquidusand solidus and concomitant segregation coefficients. We use our designs, for in situ X-ray diffractionmeasurements and melting of germanium–silicon alloys at high pressure for both a germanium-rich and asilicon-rich starting composition