Ion channels and receptors: molecular targets for behavioral evolution

Ion channels and receptors play critical roles in shaping neuronal activity, and thus are appropriate targets for evolutionary change to generate new behaviors. In this review, the evolution and differentiation of the many voltage-gated ion channels and transmitter-activated receptors is summarized; these channels and receptors evolved very early, and with some exceptions all species with nervous systems use similar sets of channels and receptors. Several examples are given of mechanisms for species-specific behavioral evolution that arise from mutations involving the structure, alternative splicing, level of expression, targeting and modulation of these important neural proteins.     

昆虫几丁质酶及其在害虫防治中的应用

几丁质是昆虫重要的结构性组分,在昆虫生长发育的各个时期都需要一定量的几丁质来维持其代谢平衡.昆虫几丁质酶可以降解昆虫体壁和围食膜中的几丁质,作为一种潜在的生物杀虫剂在害虫防治方面具有广阔的应用前景.随着对昆虫几丁质酶研究的不断深入,目前已克隆到了30余种昆虫几丁质酶,并应用于转基因作物和基因工程微生物中,对害虫具有一定...     

Insect pest control agents: Novel chiral butanoate esters (juvenogens)

During the investigation of ester derivatives (juvenogens, biochemically activated insect hormonogenic compounds) of biologically active alcohols with potential application in insect pest control, a need for availability of all existing stereoisomers of ethyl N-{2-[4-(2-butanoyloxycyclohexyl)methyl]phenoxy}ethyl carbamate occurred. They were synthesized from their chiral precursors, the corresponding stereoisomers of 2-(4-methoxybenzyl)cyclohexyl butanoate, by removing their protecting group (methyl), and by subsequent condensation of the aromatic hydroxyl moiety with ethyl N-(2-bromoethyl) carbamate. The requested enantiomers of 2-(4-methoxybenzyl)cyclohexyl butanoate were obtained by a Candida antarctica lipase-mediated transesterification and chiral resolution of the respective racemic cis- and trans-isomers of 2-(4-methoxybenzyl)cyclohexanol either directly or after a subsequent chemical esterification of the chiral precursor. In this synthesis, two convenient butanoic acid activating esters, vinyl butanoate and 2,2,2-trifluoroethyl butanoate, were employed, and the chiral precursors in the synthesis of the target molecules were obtained in 41-48% yields (i.e., 82-96% conversion), and with enantiomeric purity ee=96-98%, respectively. The enantiomeric purity of the products was determined by chiral HPLC analysis, and their absolute configuration was assigned on the basis of analyzing the (1)H and (19)F NMR spectra of their diastereoisomeric Mosher acid (3,3,3-trifluoromethyl-2-methoxy-2-phenylpropanoic acid) esters.     

CB1 and CB2 receptors are novel molecular targets for Tamoxifen and 4OH-Tamoxifen

Tamoxifen (Tam) is classified as a selective estrogen receptor modulator (SERM) and is used for treatment of patients with ER-positive breast cancer. However, it has been shown that Tam and its cytochrome P450-generated metabolite 4-hydroxy-Tam (4OH-Tam) also exhibit cytotoxic effects in ER-negative breast cancer cells. These observations suggest that Tam and 4OH-Tam can produce cytotoxicity via estrogen receptor (ER)-independent mechanism(s) of action. The molecular targets responsible for the ER-independent effects of Tam and its derivatives are poorly understood. Interestingly, similar to Tam and 4OH-Tam, cannabinoids have also been shown to exhibit anti-proliferative and apoptotic effects in ER-negative breast cancer cells, and estrogen can regulate expression levels of cannabinoid receptors (CBRs). Therefore, this study investigated whether CBRs might serve as novel molecular targets for Tam and 4OH-Tam. We report that both compounds bind to CB1 and CB2Rs with moderate affinity (0.9–3 μM). Furthermore, Tam and 4OH-Tam exhibit inverse activity at CB1 and CB2Rs in membrane preparations, reducing basal G-protein activity. Tam and 4OH-Tam also act as CB1/CB2R-inverse agonists to regulate the downstream intracellular effector adenylyl cyclase in intact cells, producing concentration-dependent increases in intracellular cAMP. These results suggest that CBRs are molecular targets for Tam and 4OH-Tam and may contribute to the ER-independent cytotoxic effects reported for these drugs. Importantly, these findings also indicate that Tam and 4OH-Tam might be used as structural scaffolds for development of novel, efficacious, non-toxic cancer drugs acting via CB1 and/or CB2Rs.     

Phosphorylation-dependent regulation of ryanodine receptors: a novel role for leucine/isoleucine zippers

Ryanodine receptors (RyRs), intracellular calcium release channels required for cardiac and skeletal muscle contraction, are macromolecular complexes that include kinases and phosphatases. Phosphorylation/dephosphorylation plays a key role in regulating the function of many ion channels, including RyRs. However, the mechanism by which kinases and phosphatases are targeted to ion channels is not well understood. We have identified a novel mechanism involved in the formation of ion channel macromolecular complexes: kinase and phosphatase targeting proteins binding to ion channels via leucine/isoleucine zipper (LZ) motifs. Activation of kinases and phosphatases bound to RyR2 via LZs regulates phosphorylation of the channel, and disruption of kinase binding via LZ motifs prevents phosphorylation of RyR2. Elucidation of this new role for LZs in ion channel macromolecular complexes now permits: (a) rapid mapping of kinase and phosphatase targeting protein binding sites on ion channels; (b) predicting which kinases and phosphatases are likely to regulate a given ion channel; (c) rapid identification of novel kinase and phosphatase targeting proteins; and (d) tools for dissecting the role of kinases and phosphatases as modulators of ion channel function.     

Regulatory roles of microRNAs in insect pests: prospective targets for insect pest control

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Tamoxifen molecular targets different from estrogen receptors

Experimental studies showing ever new biological effects of tamoxifen on tumor cells, both expressing and nonexpressing estrogen receptors, are providing a novel conception of the drug, likely well known at present. The review describes tamoxifen targets, whose blocking induces inhibition of tumor cell growth and angiogenesis, stimulation of the programmed cell death (apoptosis, autophagia and necrosis), inhibition of multiple drug resistance mechanism and inhibition of invasion and metastasizing. In all the events, the results of the tamoxifen interaction with the cells are prognostically favourable from the viewpoint of both the inhibition of the tumor growth and metastasizing and the susceptibility to the medicinal therapy, that is considered by some authors as an extremely important addition to the tamoxifen antiestrogenic effect. The strategy of long-term tamoxifen adjuvant therapy of breast cancer with positive status of the estrogen reseptors was developed by Craig V. Jordan as far back as in the seventies of the XXth century, however there are arguments allowing to consider it also useful for the treatment of other tumors. First of all it is the fact described lately in regard to expression of estrogen beta-reseptors in solid tumors of practically all known localization and histological types, that are also the targets of tamoxifen. Apart from estimation of estrogen receptors, it is believed by some authors that molecular and biological choice of patients is necessary with an account of expression of other cell targets of antiestrogen for complete realization of all the aspects of tamoxifen biological activity in long-term adjuvant therapy of malignant tumors of various localization.     

Epidermal stem cells: targets for carcinogenic chemicals

Epidermal stem cells long have been considered a target for carcinogenic chemicals, but these stem cells have never been identified or isolated. Toward this goal, this report examines two-stage carcinogenesis in light of the stem cell model for cellular replacement in the epidermis and considers characteristics that may be useful in the identification and the isolation of epidermal stem cells. Firstly, the carcinogenesis experiments in mice have indicated that the population of target cells normally remains in the epidermis for the life of the animal despite the continual cellular turnover. Hence, the slowly cycling (label-retaining) keratinocytes from the epidermis and hair follicles are potential targets. Secondly, the results of carcinogenesis experiments have also indicated that the target cells are necessarily ones with a high potential for proliferation relative the most of the proliferative population. The keratinocyte colony forming units (kCFU) from the epidermis of normal and treated adult mice are consequently a quantifiable indicator of proliferative potential and another possible target. Further application of the stem cell concepts of quiescence and of self-renewal is expected to yield additional tools for the identification and isolation of the epidermal targets for chemical carcinogens.     

A novel and rapid approach to isolating functional ryanodine receptors

Conventional methods of isolating and reconstituting ryanodine receptors (RyRs) from native membranes into proteoliposomes take a minimum of 2 days to complete. We have developed an alternative strategy that can be used to isolate and reconstitute functional RyRs in just 3 h with a similar degree of purification. RyRs isolated by this method display characteristic functional behaviour as assessed by radioligand binding and single channel analyses.     

Insect clocks: implication in an effective pest management

Abstract

Circadian rhythms are endogenous, and synchronize biological functions at the most suited time of the day. Insects like other organism display a wide array of circadian functions, which are controlled by a central timing system, in coordination with the peripheral clocks found in many tissues. Many insect behaviours including locomotion, courtship, mating, egg laying and photoperiodism, are influenced by the circadian systems. In this mini-review, we briefly describe the involvement of circadian clocks in various physiological processes and correlate their functions in insect life, focusing on lepidopteran pests (major group of Indian crop pests) and discuss their role(s) in the development of effective pest management strategy.     

Insect odorant receptors: channeling scent

Odorant detection in insects involves heterodimers between an odorant receptor (OR) and a conserved seven-transmembrane protein called Or83b, but the exact mechanism of OR signal transduction is unclear. Two recent studies in Nature (Sato et al., 2008; Wicher et al., 2008) now reveal that these OR-Or83b heterodimers form odorant-gated ion channels, revealing a surprising new mode of olfactory transduction.     

昆虫共生微生物在病虫害和疾病控制上的应用前景

昆虫与微生物之间的互利共生关系是自然界中一种常见的互作形式。昆虫的种类丰富多样并且在自然界中分布广泛,在一定程度上得益于共生微生物的帮助。随着生物技术的不断发展,越来越多的共生微生物和互利共生模式得以发现并深入研究。微生物不仅能够为昆虫的生长发育提供营养,还能合成很多生物活性物质、调节宿主的免疫、对抗捕食者和抵御病原微生物感染,成为宿主昆虫健康和适应的守护者。鉴于共生微生物与昆虫生理生态的密切联系,以及昆虫对人类经济与健康的重要影响,利用共生微生物对昆虫及虫媒病进行生物控制已经成为一个热点研究方向,并展现了良好的应用前景。本文对昆虫共生微生物的多样性、生物学功能、与宿主相互作用机制及其在病虫害和虫媒病防治中的研究进展进行综述和展望。     

Activation of skeletal ryanodine receptors by two novel scorpion toxins from Buthotus judaicus

Buthotus judaicus toxin 1 (BjTx-1) and toxin 2 (BjTx-2), two novel peptide activators of ryanodine receptors (RyR), were purified from the venom of the scorpion B. judaicus. Their amino acid sequences differ only in 1 residue out of 28 (residue 16 corresponds to Lys in BjTx-1 and Ile in BjTx-2). Despite a slight difference in EC(50), both toxins increased binding of [(3)H]ryanodine to skeletal sarcoplasmic reticulum at micromolar concentrations but had no effect on cardiac or liver microsomes. Their activating effect was Ca(2+)-dependent and was synergized by caffeine. B. judaicus toxins also increased binding of [(3)H]ryanodine to the purified RyR1, suggesting that a direct protein-protein interaction mediates the effect of the peptides. BjTx-1 and BjTx-2 induced Ca(2+) release from Ca(2+)-loaded sarcoplasmic reticulum vesicles in a dose-dependent manner and induced the appearance of long lived subconductance states in skeletal RyRs reconstituted into lipid bilayers. Three-dimensional structural modeling reveals that a cluster of positively charged residues (Lys(11) to Lys(16)) is a prominent structural motif of both toxins. A similar structural motif is believed to be important for activation of RyRs by imperatoxin A (IpTx(a)), another RyR-activating peptide (Gurrola, G. B., Arevalo, C., Sreekumar, R., Lokuta, A. J., Walker, J. W., and Valdivia, H. H. (1999) J. Biol. Chem. 274, 7879-7886). Thus, it is likely that B. judaicus toxins and imperatoxin A bind to RyRs by means of electrostatic interactions that lead to massive conformational changes in the channel protein. The different affinity and structural diversity of this family of scorpion peptides makes them excellent peptide probes to identify RyR domains that trigger the channel to open.     

Glucokinase and glucokinase regulatory proteins as molecular targets for novel antidiabetic drugs

Molecular Biology - The impairment of glucose homeostasis leads to hyperglycemia and type-2 diabetes mellitus. Glucokinase (GK), an enzyme that catalyzes the conversion of glucose to...     

The Trojan female technique: a novel,effective and humane approach for pest population control

Humankind''s ongoing battle with pest species spans millennia. Pests cause or carry disease, damage or consume food crops and other resources, and drive global environmental change. Conventional approaches to pest management usually involve lethal control, but such approaches are costly, of varying efficiency and often have ethical issues. Thus, pest management via control of reproductive output is increasingly considered an optimal solution. One of the most successful such ‘fertility control’ strategies developed to date is the sterile male technique (SMT), in which large numbers of sterile males are released into a population each generation. However, this approach is time-consuming, labour-intensive and costly. We use mathematical models to test a new twist on the SMT, using maternally inherited mitochondrial (mtDNA) mutations that affect male, but not female reproductive fitness. ‘Trojan females’ carrying such mutations, and their female descendants, produce ‘sterile-male’-equivalents under natural conditions over multiple generations. We find that the Trojan female technique (TFT) has the potential to be a novel humane approach for pest control. Single large releases and relatively few small repeat releases of Trojan females both provided effective and persistent control within relatively few generations. Although greatest efficacy was predicted for high-turnover species, the additive nature of multiple releases made the TFT applicable to the full range of life histories modelled. The extensive conservation of mtDNA among eukaryotes suggests this approach could have broad utility for pest control.     

Regulation of cardiac excitation-contraction coupling by sorcin, a novel modulator of ryanodine receptors

Activation of Ca2+ release channels/ryanodine receptors (RyR) by the inward Ca2+ current (I(Ca)) gives rise to Ca(2+)-induced Ca2+ release (CICR), the amplifying Ca2+ signaling mechanism that triggers contraction of the heart. CICR, in theory, is a high-gain, self-regenerating process, but an unidentified mechanism stabilizes it in vivo. Sorcin, a 21.6 kDa Ca(2+)-binding protein, binds to cardiac RyRs with high affinity and completely inhibits channel activity. Sorcin significantly inhibits both the spontaneous activity of RyRs in quiescent cells (visualized as Ca2+ sparks) and the I(Ca)-triggered activity of RyRs that gives rise to [Ca2+]i transients. Since sorcin decreases the amplitude of the [Ca2+]i transient without affecting the amplitude of I(Ca), the overall effect of sorcin is to reduce the "gain" of excitation-contraction coupling. Immunocytochemical staining shows that sorcin localizes to the dyadic space of ventricular cardiac myocytes. Ca2+ induces conformational changes and promotes translocation of sorcin between soluble and membranous compartments, but the [Ca2+] required for the latter process (ED50 = approximately 200 microM) appears to be reached only within the dyadic space. Thus, sorcin is a potent inhibitor of both spontaneous and I(Ca)-triggered RyR activity and may play a role in helping terminate the positive feedback loop of CICR.     

Symbiotic microorganisms: untapped resources for insect pest control

Symbiotic microorganisms offer one route to meet the anticipated heightened demand for novel insect pest management strategies created by growing human populations and global climate change. Two approaches have particular potential: the disruption of microbial symbionts required by insect pests, and manipulation of microorganisms with major impacts on insect traits contributing to their pest status (e.g. capacity to vector diseases, natural enemy resistance). Specific research priorities addressed in this article include identification of molecular targets against which highly specific antagonists can be designed or discovered, and management strategies to manipulate the incidence and properties of facultative microorganisms that influence insect pest traits. Collaboration with practitioners in pest management will ensure that the research agenda is married to agricultural and public health needs.