Flight behavior of methyl-parathion-resistant and -susceptible western corn rootworm (Coleoptera: Chrysomelidae) populations from Nebraska

Relative flight behavior of methyl-parathion-resistant and -susceptible western corn rootworm, Diabrotica virgifera virgifera LeConte populations, was studied as part of a larger effort to characterize the potential impact of insecticide resistance on adult life history traits and to understand the evolution and spread of resistance. A computer interfaced actograph was used to compare flight of resistant and susceptible individuals, and flight of resistant individuals with and without prior exposure to methyl-parathion. In each case, mean trivial and sustained flight durations were compared among treatments. In general, there were few differences in trivial or sustained flight characteristics as affected by beetle population, insecticide exposure, sex, or age and there were few significant interactions among variables. Tethered flight activity was highly variable and distributions of flight duration were skewed toward flights of short duration. Tethered flight activity was similar among resistant and susceptible beetles with the exception that susceptible beetles initiated more flights per beetle than resistant beetles. After sublethal exposure to methyl-parathion, total flight time, total trivial flight time, and mean number of flights per resistant beetle declined significantly. Because long-range flight was uncommon, short- to medium-duration flights may play an important role in determining gene flow and population spread of resistant D. v. virgifera. These results suggest that organophosphate-resistant beetles can readily move and colonize new areas, but localized selection pressure (e.g., management practices) and exposure to methyl-parathion may contribute to the small-scale differences in resistance intensity often seen in the field.     

Solution structural study of a DNA duplex containing the guanine-N7 adduct formed by a cytotoxic platinum-acridine hybrid agent

[PtCl(en)(ACRAMTU-S)](NO(3))(2) (PT-ACRAMTU; en = ethane-1,2-diamine, ACRAMTU = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) is a dual metalating/intercalating DNA binding drug conjugate that shows cytotoxicity at micromolar to nanomolar concentrations in a wide range of solid tumor cell lines. In approximately 80% of its adducts, PT-ACRAMTU binds to guanine-N7 in the major groove, selectively at 5'-CG sites [Budiman, M. E. et al. (2004) Biochemistry 43, 8560-8567]. Here, we report the synthesis, physical characterization, and NMR solution structure of a site-specifically modified octamer containing this adduct, 5'-CCTCGTCC-3'/3'-GGAGCAGG-5', where the asterisk indicates the [Pt(en)ACRAMTU)](3+) fragment. The structure was determined by a combination of high-resolution 2-D NMR spectroscopy and restrained molecular dynamics/molecular mechanics (rMD/MM) calculations using 179 NOE distance restraints and refined to an r(6) weighted residual (R(x)) of 9.2 x 10(-)(2) using the complete relaxation matrix approach. An average structure was calculated from the final ensemble of 19 rMD geometries showing pairwise root-mean-square deviations of <1.05 A. The dual binding increases the thermal stability of the octamer compared to the unmodified duplex (DeltaT(m) = 13.2 degrees ). The modified sequence shows structural features reminiscent of both B- and A-type DNA. Watson-Crick hydrogen bonding is intact at and beyond the adduct site. Platinum is bound to the N7 position of G5 in the major groove, and ACRAMTU intercalates into the central 5'-C4G5/C12G13 base-pair step on the 5'-face of the platinated nucleobase. The chromophore's long axis is aligned with the long axes of the adjacent base pairs, maximizing intermolecular pi-pi stacking interactions. PT-ACRAMTU lengthens (rise, 6.62 A) and unwinds (twist, 15.4 degrees ) the duplex at the central base-pair step but does not cause helical bending. No C3'-endo deoxyribose pucker and no significant roll are observed at the site of intercalation/platination, which clearly distinguishes the PT-ACRAMTU-induced damage from the 1,2-intrastrand cross-link formed by cisplatin. Overall, the DNA perturbations produced by PT-ACRAMTU do not appear to mimic those caused by the major cisplatin lesion. Instead, intriguing structural similarities are observed for PT-ACRAMTU's monoadduct and the N7 adducts of dual major-groove alkylating/intercalating antitumor agents, such as the pluramycins.     

The catalytically active serine protease domain of human complement factor I

Factor I (fI) is a major regulator of complement. As a protease it has very restricted specificity, cleaving only C3b or C4b in the presence of a cofactor such as factor H (fH). Cleavage of C3b by fI yields iC3b, a major opsonin. The cleavage occurs through the formation of a ternary complex between the enzyme, the substrate, and the cofactor. The catalytic subunit of fI, the SP domain, accommodates substrate recognition and cleavage. The role of the fI heavy chain within the catalysis complex is unknown. Using partial proteolysis and affinity chromatography an intact form of the SP domain was generated and isolated from fI in high yield. fI and the SP domain were found to have similar amidolytic activities but strikingly different proteolytic activities on C3(NH(3)). fI did not cleave C3(NH(3)) in the absence of fH, while in its presence it cleaved C3(NH(3)) rapidly at two sites. The SP domain, however, slowly cleaved C3(NH(3)) in the absence of fH, at more than two sites. Cleavage by the SP domain was inhibited, not stimulated, by fH. Pefabloc SC and antipain inhibited the proteolytic activity of both fI and the SP domain, but suramin inhibited only fI and not the SP domain. The contrast in the proteolytic activities suggests that the heavy chain domains and the cofactor must have roles in orienting the natural substrates and restricting cleavage to the two sites which yield iC3b through a highly specific catalysis.     

Ecogeographic size variations in Sifakas: a test of the resource seasonality and resource quality hypotheses

Ecogeographic size variations have been documented in some but not all sifakas. Few morphometric or body weight data have been available for two critically endangered subspecies of diademed sifakas: Perrier's sifakas (Propithecus diadema perrieri) and silky sifakas (Propithecus diadema candidus). The objectives of our study were to determine size variations in sifakas and if these variations are related to resource quality and/or resource seasonality. P. d. perrieri and P. d. candidus were captured, weighed, and measured in northern Madagascar. Body weights and morphometrics were compared with other subspecies of diademed sifakas and indris (Indri indri). Differences in body weights and morphometrics between taxa are particularly pronounced for P. d. perrieri compared to P. d. diadema, P. d. edwardsi, and I. indri. Most morphometrics varied in comparisons between P. d. candidus and the other Indriidae (P. d. diadema, P. d. edwardsi, and I. indri). Average body size in sifakas is positively correlated with annual rainfall and negatively correlated with length of dry season. Sifaka body size is not correlated with protein-to-fiber ratios. Thus, size variations in sifakas are related to resource seasonality rather than resource quality. The relationships between the temporal availability of food resources and sifaka body size reflect complex and regionally varying causalities. Detailed, longitudinal information on the ecological factors underlying food selection and nutrient requirements in sifakas are needed to determine the relationship between ecogeographic variables and body size in sifakas.     

Crystal structure of homoserine transacetylase from Haemophilus influenzae reveals a new family of alpha/beta-hydrolases

Homoserine transacetylase catalyzes one of the required steps in the biosynthesis of methionine in fungi and several bacteria. We have determined the crystal structure of homoserine transacetylase from Haemophilus influenzae to a resolution of 1.65 A. The structure identifies this enzyme to be a member of the alpha/beta-hydrolase structural superfamily. The active site of the enzyme is located near the end of a deep tunnel formed by the juxtaposition of two domains and incorporates a catalytic triad involving Ser143, His337, and Asp304. A structural basis is given for the observed double displacement kinetic mechanism of homoserine transacetylase. Furthermore, the properties of the tunnel provide a rationale for how homoserine transacetylase catalyzes a transferase reaction vs hydrolysis, despite extensive similarity in active site architecture to hydrolytic enzymes.     

IFN-alpha beta secreted during infection is necessary but not sufficient for negative feedback regulation of IFN-alpha beta signaling by Mycobacterium tuberculosis

IFN-alphabeta functions in the transition from innate to adaptive immunity and may impinge on the interaction of Mycobacterium tuberculosis with its host. Infection by M. tuberculosis causes IFN-alphabeta secretion and down-regulation of IFN-alphabeta signaling in human APC and the human monocytic cell line THP-1, which provides a model for these studies. Neutralization of secreted IFN-alphabeta prevents inhibition of IFN-alpha signaling during infection, but several lines of evidence distinguish inhibition due to infection from a negative feedback response to only IFN-alphabeta. First, greater inhibition of IFN-alpha-stimulated STAT-1 tyrosine phosphorylation occurs 3 days postinfection than 1 or 3 days after IFN-alphabeta pretreatment. Second, LPS also induces IFN-alphabeta secretion and causes IFN-alphabeta-dependent down-regulation of IFN-alpha signaling, yet the inhibition differs from that caused by infection. Third, IFN-alpha signaling is inhibited when cells are grown in conditioned medium collected from infected cells 1 day postinfection, but not if it is collected 3 days postinfection. Because IFN-alphabeta is stable, the results with conditioned medium suggest the involvement of an additional, labile substance during infection. Further characterizing signaling for effects of infection, we found that cell surface IFN-alphabeta receptor is not reduced by infection, but that infection increases association of protein tyrosine phosphatase 1c with the receptor and with tyrosine kinase 2. Concomitantly, IFN-alpha stimulation of tyrosine kinase 2 tyrosine phosphorylation and kinase activity decreases in infected cells. Moreover, infection reduces the abundance of JAK-1 and tyrosine-phosphorylated JAK-1. Thus, the distinctive down-regulation of IFN-alpha signaling by M. tuberculosis occurs together with a previously undescribed combination of inhibitory intracellular events.     

The chemokines CXCL9, CXCL10, and CXCL11 differentially stimulate G alpha i-independent signaling and actin responses in human intestinal myofibroblasts

Intestinal myofibroblasts have been implicated in the pathogenesis of chronic inflammatory conditions such as Crohn's disease via interactions with an elaborate network of cytokines, growth factors, and other inflammatory mediators. CXCR3 is a Galpha(i) protein-coupled receptor that binds the proinflammatory chemokines CXCL9, CXCL10, and CXCL11, which are released from the intestinal epithelium. The three CXCR3 ligands shared the ability to activate biochemical (e.g., PI3K and MAPK activation) and functional events (actin reorganization) in intestinal myofibroblasts. However, CXCL11 is unique in its ability to elevate intracellular calcium. Surprisingly, although CXCR3 mRNA is detectable in these myofibroblasts, there is no detectable surface expression of CXCR3. Furthermore, the biochemical responses and actin reorganization stimulated by the CXCR3 ligands in intestinal myofibroblasts are insensitive to the Galpha(i) inhibitor, pertussis toxin. This suggests either the existence of differential receptor coupling mechanisms in myofibroblasts for CXCR3 that are distinct from those observed in PBLs and/or that these cells express a modified or variant CXCR3 compared with the CXCR3 expressed on PBLs.