A method for testing compressive properties of single proteoglycan aggregates

This study presents a method for direct measurement of the compressive properties of single molecules of proteoglycan aggregate using a state-of-the-art laser tweezers/interferometer system previously developed to test the tensile properties of single molecules. A typical molecule of proteoglycan aggregate showed a highly non-linear resistance to compression after being compressed to about 25% of its original molecule length.     

Assignment of paternity groups without access to parental genotypes: multiple mating and developmental plasticity in squid

We present a novel approach to investigating sibling relationships and reconstructing parental genotypes from a progeny array. The Bayesian method we have employed is flexible and may be applicable to a variety of situations in addition to the one presented here. While mutation rates and breeding population allele frequencies can be taken into account, the model requires relatively few loci and makes few assumptions. Paternity of 270 veined squid (Loligo forbesi) hatchlings from three egg strings collected from one location was assigned using five microsatellite loci. Paternal and maternal genotypes reconstructed for each of the three strings were identical, strongly indicating that a single female produced the strings that were fertilized by the same four males. The proportion of eggs fertilized was not equal between males in all three strings, with male 1 siring most offspring (up to 68% in string 1), through to male 4 siring the least (as low as 2.4% in string 1). Although temperature had a profound effect on incubation time, paternity did not affect this trait at 12 degrees C or 8 degrees C.     

Site-directed mutations of human hemoglobin at residue 35beta: a residue at the intersection of the alpha1beta1, alpha1beta2, and alpha1alpha2 interfaces

Because Tyr35beta is located at the convergence of the alpha1beta1, alpha1beta2, and alpha1alpha2 interfaces in deoxyhemoglobin, it can be argued that mutations at this position may result in large changes in the functional properties of hemoglobin. However, only small mutation-induced changes in functional and structural properties are found for the recombinant hemoglobins betaY35F and betaY35A. Oxygen equilibrium-binding studies in solution, which measure the overall oxygen affinity (the p50) and the overall cooperativity (the Hill coefficient) of a hemoglobin solution, show that removing the phenolic hydroxyl group of Tyr35beta results in small decreases in oxygen affinity and cooperativity. In contrast, removing the entire phenolic ring results in a fourfold increase in oxygen affinity and no significant change in cooperativity. The kinetics of carbon monoxide (CO) combination in solution and the oxygen-binding properties of these variants in deoxy crystals, which measure the oxygen affinity and cooperativity of just the T quaternary structure, show that the ligand affinity of the T quaternary structure decreases in betaY35F and increases in betaY35A. The kinetics of CO rebinding following flash photolysis, which provides a measure of the dissociation of the liganded hemoglobin tetramer, indicates that the stability of the liganded hemoglobin tetramer is not altered in betaY35F or betaY35A. X-ray crystal structures of deoxy betaY35F and betaY35A are highly isomorphous with the structure of wild-type deoxyhemoglobin. The betaY35F mutation repositions the carboxyl group of Asp126alpha1 so that it may form a more favorable interaction with the guanidinium group of Arg141alpha2. The betaY35A mutation results in increased mobility of the Arg141alpha side chain, implying that the interactions between Asp126alpha1 and Arg141alpha2 are weakened. Therefore, the changes in the functional properties of these 35beta mutants appear to correlate with subtle structural differences at the C terminus of the alpha-subunit.     

Dothistroma pini,a forest pathogen,contains homologs of aflatoxin biosynthetic pathway genes

Homologs of aflatoxin biosynthetic genes have been identified in the pine needle pathogen Dothistroma pini. D. pini produces dothistromin, a difuranoanthraquinone toxin with structural similarity to the aflatoxin precursor versicolorin B. Previous studies with purified dothistromin suggest a possible role for this toxin in pathogenicity. By using an aflatoxin gene as a hybridization probe, a genomic D. pini clone was identified that contained four dot genes with similarity to genes in aflatoxin and sterigmatocystin gene clusters with predicted activities of a ketoreductase (dotA), oxidase (dotB), major facilitator superfamily transporter (dotC), and thioesterase (dotD). A D. pini dotA mutant was made by targeted gene replacement and shown to be severely impaired in dothistromin production, confirming that dotA is involved in dothistromin biosynthesis. Accumulation of versicolorin A (a precursor of aflatoxin) by the dotA mutant confirms that the dotA gene product is involved in an aflatoxin-like biosynthetic pathway. Since toxin genes have been found to be clustered in fungi in every case analyzed so far, it is speculated that the four dot genes may comprise part of a dothistromin biosynthetic gene cluster. A fifth gene, ddhA, is not a homolog of aflatoxin genes and could be at one end of the dothistromin cluster. These genes will allow comparative biochemical and genetic studies of the aflatoxin and dothistromin biosynthetic pathways and may also lead to new ways to control Dothistroma needle blight.     

The structure of arylamine N-acetyltransferase from Mycobacterium smegmatis--an enzyme which inactivates the anti-tubercular drug,isoniazid

Arylamine N-acetyltransferases which acetylate and inactivate isoniazid, an anti-tubercular drug, are found in mycobacteria including Mycobacterium smegmatis and Mycobacterium tuberculosis. We have solved the structure of arylamine N-acetyltransferase from M. smegmatis at a resolution of 1.7 A as a model for the highly homologous NAT from M. tuberculosis. The fold closely resembles that of NAT from Salmonella typhimurium, with a common catalytic triad and domain structure that is similar to certain cysteine proteases. The detailed geometry of the catalytic triad is typical of enzymes which use primary alcohols or thiols as activated nucleophiles. Thermal mobility and structural variations identify parts of NAT which might undergo conformational changes during catalysis. Sequence conservation among eubacterial NATs is restricted to structural residues of the protein core, as well as the active site and a hinge that connects the first two domains of the NAT structure. The structure of M. smegmatis NAT provides a template for modelling the structure of the M. tuberculosis enzyme and for structure-based ligand design as an approach to designing anti-TB drugs.     

IL-13-induced chemokine responses in the lung: role of CCR2 in the pathogenesis of IL-13-induced inflammation and remodeling

IL-13 stimulates inflammatory and remodeling responses and contributes to the pathogenesis of human airways disorders. To further understand the cellular and molecular events that mediate these responses, we characterized the effects of IL-13 on monocyte chemotactic proteins (MCPs) and compared the tissue effects of transgenic IL-13 in mice with wild-type (+/+) and null (-/-) CCR2 loci. Transgenic IL-13 was a potent stimulator of MCP-1, -2, -3, and -5. This stimulation was not specific for MCPs because macrophage-inflammatory protein (MIP)-1alpha, MIP-1beta, MIP-2, MIP-3alpha, thymus- and activation-regulated chemokine, thymus-expressed chemokine, eotaxin, eotaxin 2, macrophage-derived chemokines, and C10 were also induced. The ability of IL-13 to increase lung size, alveolar size, and lung compliance, to stimulate pulmonary inflammation, hyaluronic acid accumulation, and tissue fibrosis, and to cause respiratory failure and death were markedly decreased, whereas mucus metaplasia was not altered in CCR2(-/-) mice. CCR2 deficiency did not decrease the basal or IL-13-stimulated expression of target matrix metalloproteinases or cathepsins but did increase the levels of mRNA encoding alpha1-antitrypsin, tissue inhibitor of metalloproteinase-1, -2, and -4, and secretory leukocyte proteinase inhibitor. In addition, the levels of bioactive and total TGF-beta(1) were decreased in lavage fluids from IL-13 transgenic mice with -/- CCR2 loci. These studies demonstrate that IL-13 is a potent stimulator of MCPs and other CC chemokines and document the importance of MCP-CCR2 signaling in the pathogenesis of the IL-13-induced pulmonary phenotype.     

Structure-based design of a potent purine-based cyclin-dependent kinase inhibitor

Aberrant control of cyclin-dependent kinases (CDKs) is a central feature of the molecular pathology of cancer. Iterative structure-based design was used to optimize the ATP- competitive inhibition of CDK1 and CDK2 by O(6)-cyclohexylmethylguanines, resulting in O(6)-cyclohexylmethyl-2-(4'- sulfamoylanilino)purine. The new inhibitor is 1,000-fold more potent than the parent compound (K(i) values for CDK1 = 9 nM and CDK2 = 6 nM versus 5,000 nM and 12,000 nM, respectively, for O(6)-cyclohexylmethylguanine). The increased potency arises primarily from the formation of two additional hydrogen bonds between the inhibitor and Asp 86 of CDK2, which facilitate optimum hydrophobic packing of the anilino group with the specificity surface of CDK2. Cellular studies with O(6)-cyclohexylmethyl-2-(4'- sulfamoylanilino) purine demonstrated inhibition of MCF-7 cell growth and target protein phosphorylation, consistent with CDK1 and CDK2 inhibition. The work represents the first successful iterative synthesis of a potent CDK inhibitor based on the structure of fully activated CDK2-cyclin A. Furthermore, the potency of O(6)-cyclohexylmethyl-2-(4'- sulfamoylanilino)purine was both predicted and fully rationalized on the basis of protein-ligand interactions.     

Stimulation of the gastrin-cholecystokinin(B) receptor promotes branching morphogenesis in gastric AGS cells

Epithelial organization is maintained by cell proliferation, migration, and differentiation. In the case of the gastric epithelium, at least some of these events are regulated by the hormone gastrin. In addition, gastric epithelial cells are organized into characteristic tubular structures (the gastric glands), but the cellular mechanisms regulating the organization of tubular structures (sometimes called branching morphogenesis) are uncertain. In the present study, we examined the role of the gastrin-cholecystokinin(B) receptor in promoting branching morphogenesis of gastric epithelial cells. When gastric cancer AGS-G(R) cells were cultured on plastic, gastrin and PMA stimulated cell adhesion, formation of lamellipodia, and extension of long processes in part by activation of protein kinase C (PKC) and phosphatidylinositol (PI)-3 kinase. Branching morphogenesis was not observed in these circumstances. However, when cells were cultured on artificial basement membrane, the same stimuli increased the formation of organized multicellular arrays, exhibiting branching morphogenesis. These effects were reversed by inhibitors of PKC but not of PI-3 kinase. We conclude that, in the presence of basement membrane, activation of PKC by gastrin stimulates branching morphogenesis.