Actin' like actin?

The most biologically significant property of actin is its ability to self-associate and form two-stranded polymeric microfilaments. In living cells, these micro filaments form the actin cytoskeleton, essential for maintenance of the shape, passive mechanical properties and active motility of eukaryotic cells. Recently discovered actin-related proteins (ARPs) appear to share a common ancestor with conventional actin. At present, six classes of ARPs have been discovered, three of which have representatives in diverse species across eukaryotic phyla and may share functional characteristics with conventional actin. The three most ubiquitous ARPs are predicted to share a common core structure with actin and contain all the residues required for ATP binding. Surface residues involved in protein protein interactions, however, have diverged. Models of these proteins based on the atomic structure of actin provide some clues about how ARPs interact with each other, with conventional actin and with conventional actin-binding proteins.     

Suppression of Pythium Root Rot of Cucumber by a Fluorescent Pseudomonad s Related to Reduced Root Colonization by Pythium Apbanidermatum

Root colonization of cucumber with P aphanidermatum OP4 was examined in the absence and in the presence of either fluorescent pseudomonad strain CH31 or strain CHI. Quantification was performed by antigen-coated plate enzyme-linked immunosorbent assay (ACP-ELISA) using an antiserum obtained from a rabbit immunized with zoospore cysts: this antiserum did not cross-react with non-infested roots of cucumber, or with the fluorescent pseudomonads CH31 and CHI. Application of the previously developed biotest enabled us to assess the ability of the two strains of fluorescent pseudomonad to suppress root rot caused by P. aphanidermaium OP4.
At all bacterial densities tested, the fluorescent pseudomonad CH31 led to a significant reduction of both the root colonization of cucumber with P aphanidermatum OP4 and the severity of Pythium root rot. In contrast, the fluorescent pseudomonad CHI had no effect on either root colonization oe disease sevenity.     

Dextran production by Leuconostoc mesenteroides in the presence of a dextranase producing yeast, Lipomyces starkeyi

Summary A new process for the production of small size dextran is developed in which dextran is produced by cultures of Leuconostoc mesenteroides in the presence of a partially constitutive mutant of Lipomyces starkeyi producing dextranase. Mixed cultures were examined by scanning electron microscopy with ruthenium to show the effects of the mixed culture on low molecular weight dextran (M.W. of 5,000 – 100,000) formation. The presence of the size variation in dextran was confirmed by gel permeation chromatography.     

Tumor marker disaccharide D-Gal-beta 1, 3-GalNAc complexed to heat-labile enterotoxin from Escherichia coli.

Heat-labile enterotoxin (LT) is part of the cholera toxin (CT) family and consists of a catalytic A subunit and a B pentamer that serves to recognize the oligosaccharide part of the GM1 ganglioside receptor. We report here the crystal structure of heat-labile enterotoxin in complex with the disaccharide portion of the Thomsen-Friedenreich (T-antigen) tumor marker. The toxin:carbohydrate complex is determined to 2.13 A resolution, yielding an R-factor of 18.5%. The T-antigen disaccharide, D-Gal-beta 1,3-GalNAc-Ser/Thr, is present in more than 85% of human carcinomas and monitoring its autoimmune response is used for the early detection of tumors. Insight into the molecular recognition of this tumor antigen by sugar binding proteins can benefit the development of a diagnostic tool for human carcinomas as well as a T-antigen directed anticancer drug delivery system.     

Effects of Interactions BetweenPasteurella haemolyticaandBordetella parapertussisonin vitroPhagocytosis by Lung Macrophages

The aim of the work was to determine the effect of exposing ovine bronchoalveolar macrophages (BAM)in vivotoPasteurella haemolyticaand/orBordetella parapertussison the subsequent uptake and killing ofP. haemolyticaby these cellsin vitro. Exposurein vivotoP. haemolyticadid not affect the uptake ofP. haemolyticaby BAMin vitrobut reduced (P< 0·05) the intracellular killing of bacteria. Exposurein vivotoB. parapertussishad no significant effect on either the uptake of killing ofP. haemolytica in vitro. However, sequential exposurein vivotoB. parapertussisandP. haemolyticareduced both the ingestion (P< 0·05) and killing (P< 0·001) ofP. haemolytica in vitro. These results indicate that exposure toP. haemolyticacompromised the bacterial killing mechanisms of BAM and that synergy betweenB. parapertussisandP. haemolyticareduced the ability of BAM to ingest bacteria.     

MEMBRANE LIFTING TECHNIQUE FOR RAPID DETECTION OF ESCHERICHIA COLI 0157:H7 IN INOCULATED GROUND MEATS

A membrane lifting technique was developed for direct rapid detection of Escherichia coli 0157:H7 in inoculated ground meats. Duplicate groups of 2 meatballs were inoculated with volumes of 0.1-ml of a serial dilution (1:10) of E. coli 0157:H7 or a mixed culture containing one strain of E. coli 0157:H7 and a non-0157:H7E. coli serotype (E. coli ATCC 25922). Each meatball was sampled by sandwiching with 2 pieces of nitrocellulose membranes and pressing against each other to the center of the meatball. The membranes were in contact with the meats for 10 min to lift the bacteria. The membranes were removed and incubated on MacConkey-sorbitol agar plates with the meat contact side up. After 18 h incubation at 37C, an immunostain was performed directly on the membranes for detection of the presence or absence of E. coli 0157:H7. This method was found to be sensitive enough to detect as few as 1 to 2 cells of E. coli 0157:H7 inoculated on surfaces of 18-g meatballs. This method might be used as a rapid presumptive test for E. coli 0157:H7.     

Relationships among didelphid marsupials based on sequence variation in the mitochondrial cytochrome B gene

Variation in the mitochondrial cytochrome b gene (nucleotide and amino acid sequences) is evaluated for 9 genera and 15 species of American opossums in the family Didelphidae, using the American caenolestid rat opossumLestoros and the New Guinean peroryctid bandicootEchimypera as outgroups. Phylogenetic analyses (parsimony and distance) strongly support the monophyly of the Didelphidae and delineate two major clades; (1)Didelphis andPhilander are strongly aligned sister taxa, withMetachirus weakly but consistently associated with them, and (2)Marmosa plusMicoureus, withMonodelphis falling outside that pair. The generaMarmosops, Caluromys, andGlironia exhibit varied relationships, depending upon the method of analysis and data (DNA or amino acid sequences) used, but generally are placed individually or in combinations near or at the base of the didelphid radiation. Some aspects of these relationships are consistent with current taxonomic views, but others are in marked contrast. Specifically, a clade comprised of the mouse opossumsMarmosa, Micoureus, andMarmosops is strongly rejected by log-likelihood analysis, contrary to expectations from some current classifications. Also, the woolly opossumsCaluromys andGlironia also do not form a sister-taxon relationship, as suggested by their placement in a subfamily separate from the remaining didelphids examined. However, such a relationship cannot be rejected from log-likelihood analyses. The relationships suggested fromcyt-b sequences are strongly concordant with those based on DNA-DNA hybridization analyses. In addition to systematic and phylogenetic properties, molecular evolution of the didelphid cytochrome b gene sequence is characterized according to nucleotide bias and rate differentials at each codon position and across the entire sequence.To whom correspondence should be addressed.     

Insulin-like growth factor I levels decrease in the development of diabetes inMacaca nigra

Members of the monkey speciesMacaca nigra spontaneously develop impairments in insulin secretion and glucose clearance, and eventually become overtly diabetic. Changes in certain metabolic signals such as clearance of glucose and insulin increment secreted in an intravenous glucose tolerance test have allowed the identification of four stages in the progression from non-diabetes to diabetes in monkeys — non-diabetic, hormonally impaired, borderline diabetic, and diabetic. Recently, another metabolic stage, hyperinsulinemic, was also identified in these animals. In recent years, other factors besides those listed above have been implicated to be correlated with the metabolic progression from a nondiabetic to a diabetic state. One of these factors, is insulin like growth factor I (IGF-I). In diabetic humans who are in poor metabolic control, and in rats with streptozotocin induced ketotic diabetes, serum levels of IGF-I are lowered by as much as 40–50% of control non-diabetics. If indeed decreased IGF-I levels are correlated with the onset of diabetes then changes in IGF-I concentrations prior to the clinically diagnosed disease state would be expected. Using serum samples collected from different animals in a colony ofMacaca nigra in a variety of metabolic states, we have found that IGF-I and insulin levels decrease in each defined metabolic state as the animals progress from nondiabetic to diabetic. Since IGF-I and insulin levels decrease in a similar fashion in the progression of this disease then this maybe indicative of the coordinate expression of these two factors.