Structural features of the G-protein/GPCR interactions

Background

The details of the functional interaction between G proteins and the G protein coupled receptors (GPCRs) have long been subjected to extensive investigations with structural and functional assays and a large number of computational studies.

Scope of review

The nature and sites of interaction in the G-protein/GPCR complexes, and the specificities of these interactions selecting coupling partners among the large number of families of GPCRs and G protein forms, are still poorly defined.

Major conclusions

Many of the contact sites between the two proteins in specific complexes have been identified, but the three dimensional molecular architecture of a receptor-Gα interface is only known for one pair. Consequently, many fundamental questions regarding this macromolecular assembly and its mechanism remain unanswered.

General significance

In the context of current structural data we review the structural details of the interfaces and recognition sites in complexes of sub-family A GPCRs with cognate G-proteins, with special emphasis on the consequences of activation on GPCR structure, the prevalence of preassembled GPCR/G-protein complexes, the key structural determinants for selective coupling and the possible involvement of GPCR oligomerization in this process.     

Vibrio madracius sp. nov. Isolated from Madracis decactis (Scleractinia) in St Peter & St Paul Archipelago,Mid-Atlantic Ridge,Brazil

Three novel isolates (A-354^T, A-328, and A-384) were retrieved from apparently healthy scleractinian Madracis decactis in the remote St Peter & St Paul Archipelago, Mid-Atlantic Ridge, Brazil. The novel isolates formed a distinct lineage based on the phylogenetic reconstruction using the 16S rRNA and pyrH gene sequences. They fell into the Mediterranei clade and their closest phylogenetic neighbour was V. mediterranei species, sharing upto 98.1 % 16S rRNA gene sequence similarity. Genomic analysis including in silico DDH, MLSA, AAI and genomic signature distinguished A-354^T from V. mediterranei LMG 19703 (=AK1) with values of 33.3, 94.2, 92 %, and 11.3, respectively. Phenotypically, the novel isolates can be differentiated from V. mediterranei based on the four following features. They do not grow at 8 % NaCl; use d-gluconic acid but not l-galactonic acid lactone as carbon source; and do not have the fatty acid C_18:0. Differentiation from both the other Mediterranei clade species (V. maritimus and V. variabilis) is supported by fifteen features. The novel species show lysine decarboxylase and tryptophan deaminase, but not gelatinase and arginine dihydrolase activity; produce acetoin; use α-d-lactose, N-acetyl-d-galactosamine, myo-Inositol, d-gluconic acid, and β-hydroxy-d,l-butyric acid; and present the fatty acids C_14:0 iso, C_15:0 anteiso, C_16:0 iso, C_17:0 anteiso, and C_17:1x8c . Whole-cell protein profiles, based on MALDI-TOF, showed that the isolates are not clonal and also distinguished them from the closes phylogenetic neighbors. The name Vibrio madracius sp. nov. is proposed to encompass these novel isolates. The G+C content of the type strain A-354^T (=LMG 28124^T=CBAS 482^T) is 44.5 mol%.     

Dietary overlap among early juvenile stages in an Antarctic notothenioid fish assemblage at Potter Cove,South Shetland Islands

To date, studies of food overlap in Antarctic fish have been performed on a mixture of late juvenile and adult stages, leaving the young immature specimens (TL ≤ 10 cm) practically unexplored. We studied diet overlap and potential competition among early juvenile individuals in a coastal notothenioid community at Potter Cove, by analysing the stomach contents of 225 fish of 5 species collected in the summer of 2009–2010. We used frequency of occurrence (F %) and the coefficient “Q” for diet evaluation and the method of Tyler and the similarity index “S” for food overlap. Amphipods of the suborder Gammaridea were the main (Q > 2.900) and most frequent (% F) prey for all species, although Notothenia coriiceps also consumed gastropods of the family Littorinidae, mostly Laevilitorina antarctica. Secondary prey were algae for Notothenia rossii and N. coriiceps, calanoid (pelagic) and harpacticoid (benthic) copepods for Trematomus newnesi and the latter copepods and isopods of the family Munnidae for Lepidonotothen nudifrons. The reoccurrence of prey among fish species was 39.6 % and food overlap between 90 % of species pairs was under 58 %. Because similarly low values of diet overlap were reported for intermediate/advanced juveniles and adults of the same species at the same site, we conclude that there is no difference in the degree of interspecific food overlap and therefore potential competition between the immature and mature fraction of the fish community. Food competition is avoided by resource partitioning along a depth gradient or by different prey species.     

How Old are Colonizing Hypothenemus hampei (Ferrari) Females When They Leave the Native Coffee Fruit?

The age of colonizing Hypothenemus hampei (Ferrari) females when they leave the native coffee fruit was determined under laboratory conditions. This biological parameter might be useful for planning experiments with this species because certain physiological statuses are expressed from or until a determined age, which in turn may determine the response of individuals to different treatments. An experimental device was used to simulate the conditions inside a coffee berry and to permit the observation of the abandonment behavior of the beetles. Virgin and mated females with or without melanized cuticles were used in the experiments. On average, colonizing coffee berry borers were 15-days-old at the moment of host abandonment. Females at this age were mated, had full dark cuticles, and were able to display flight and lay viable eggs. Interestingly, H. hampei females that mated before they acquire a fully dark cuticle abandoned the host 1.7 times faster than females that mated after they reach this physiological status. Further studies into food conditions and their impacts on the pre- abandonment of H. hampei females are encouraged.     

96-well microtiter plates for biofouling simulation in biomedical settings

Microtiter plates with 96 wells are routinely used in biofilm research mainly because they enable high-throughput assays. These platforms are used in a variety of conditions ranging from static to dynamic operation using different shaking frequencies and orbital diameters. The main goals of this work were to assess the influence of nutrient concentration and flow conditions on biofilm formation by Escherichia coli in microtiter plates and to define the operational conditions to be used in order to simulate relevant biomedical scenarios. Assays were performed in static mode and in incubators with distinct orbital diameters using different concentrations of glucose, peptone and yeast extract. Computational fluid dynamics (CFD) was used to simulate the flow inside the wells for shaking frequencies ranging from 50 to 200?rpm and orbital diameters from 25 to 100?mm. Higher glucose concentrations enhanced adhesion of E. coli in the first 24?h, but variation in peptone and yeast extract concentration had no significant impact on biofilm formation. Numerical simulations indicate that 96-well microtiter plates can be used to simulate a variety of biomedical scenarios if the operating conditions are carefully set.     

Composition and Activity against Oral Pathogens of the Essential Oil of Melampodium divaricatum (Rich.) DC.

The chemical composition of the essential oil isolated from the aerial parts of Melampodium divaricatum (Rich .) DC. (Asteraceae) was characterized by GC‐FID and GC/MS analyses. (E)‐Caryophyllene (56.0%), germacrene D (12.7%), and bicyclogermacrene (9.2%) were identified as the major oil components. The antimicrobial activity of the oil against seven standard strains of oral pathogens from the American Type Culture Collection (ATCC) was evaluated by determining minimum inhibitory concentrations (MICs) using the microdilution method. MIC Values below 100 μg/ml were obtained against Streptococcus sobrinus (90 μg/ml), Lactobacillus casei (30 μg/ml), S. mutans (20 μg/ml), and S. mitis (18 μg/ml). In contrast, the MIC values of the major oil compound (E)‐caryophyllene were higher than 400 μg/ml against all pathogens, suggesting that the activity of the oil might depend on minor oil components and/or on synergistic effects. The M. divaricatum essential oil is a promising agent to include in anticariogenic oral rinse formulations for the control of oral pathogens.     

Predators and livestock reduce bird nest survival in intensive Mediterranean farmland

High nest predation is one of the factors potentially driving farmland bird declines, particularly in the case of ground-nesting species. Accordingly, recent calls have been made to address predation in agri-environment schemes, but this is hindered by limited understanding of how processes operating at different scales affect predation patterns and how additional factors such as livestock trampling contribute to reduced nest survival. Using an artificial nest experiment, we assessed how field management, landscape composition and configuration, and the abundance of potential avian predators and mammalian carnivores affected predation and trampling rates in grassland fields (pastures and fallows) embedded in intensive Mediterranean farmland. Mean predation and trampling rates per field were 0.18?±?0.23 SD and 0.12?±?0.17 SD, respectively. However, there was strong spatial variation, with high nest losses (>50 %) occurring in about one quarter of the fields. Variation in failure rates was mainly related to livestock grazing and predator abundances, while the effects of landscape context were negligible. Predation and trampling rates were highest in fields with short swards. Predation rate was positively related to the abundance of Egyptian mongooses and dogs. To increase nest survival, agri-environment schemes designed for ground-nesting birds should contribute for maintaining low stocking density. Further evaluation is required on the need for controlling populations of fast-expanding generalist predators such as mongooses.