Affinity ligand selection from a library of small molecules: assay development, screening, and application

A facile and cost-effective process for screening synthetic libraries for an affinity ligand is described. A high throughput 96-well plate filtration method was designed to screen both discrete compounds and mixtures of compounds attached to a solid support. Human serum albumin (HSA) was used as a target protein to demonstrate the proof of concept. Detection and quantitation by fluorescence was accomplished with the use of fluorescamine to conjugate the protein in the filtrate. It is found that mixtures demonstrating low average binding reflect an overall lower hit rate of the components, whereas deconvolution of mixtures with high protein binding consistently provides a high hit rate. This differs from many of the previous experiences screening solid-phase mixtures in which high false positive rates are noted to occur. A total of 100K compounds were tested: 25K as discrete samples and 75K as mixtures. An overall hit rate of 8% was observed. Secondary screening of compounds measured specificity, recovery, and dynamic binding capacity. The effectiveness of the method is illustrated using an affinity column made with a representative lead compound. A similar purity was achieved in a single-step purification of HSA from serum as compared to that obtained by two steps of ion-exchange chromatography. The process for primary screening of a large number of compounds is simple, inexpensive, and applicable to any soluble target protein of known or unknown function from crude mixtures and may have additional utility as a generic chemical affinity tool for the functional characterization of novel proteins emerging from proteomics work.     

Female-specific regulation of cuticular hydrocarbon biosynthesis by dopamine in Drosophila melanogaster

The role of dopamine (DA) is investigated in cuticular hydrocarbon biosynthesis in Drosophila melanogaster with three different approaches: use of DA-deficient mutants (dopa decarboxylase temperature sensitive mutants reared at restrictive temperature, and rescued by dopamine ingestion or by pale mutants partially rescued by a tyrosine hydroxylase construction), pharmacological treatments (tyrosine hydroxylase inhibitors) and topical application on decapitated flies. We report that DA specifically regulates diene hydrocarbon biosynthesis, which is female specific. Our results suggest that DA acts in adult flies within the first hours of imaginal life and that DA production from the brain is crucial for this process. Thus, DA contributes to reproduction in D. melanogaster by acting during a critical period during development of young adults.     

Immobilization of a novel antibacterial agent on solid phase and subsequent isolation of EF-Tu

Screening of our compound collection identified PNU-92560, a 2-[1,3,4]thiadiazolo[3,2-a]pyrimidine-6-carboxamide, as a novel antibacterial agent. Extensive analogue development identified that the 2-position of the thiadiazole could be functionalized with a linker that would allow the compound to be attached to a solid support. The extreme insolubility of the analogues prevented the mechanism of action for these compounds to be determined utilizing traditional methodology. The solid-supported compounds were utilized as affinity columns to identify elongation factor Tu (EF-Tu) as a putative target for this class of compounds. The activity of the compounds in a metabolic labeling experiments and in translation assay supports the identity of the target for these compounds to be EF-Tu.     

Bmp7 regulates branching morphogenesis of the lacrimal gland by promoting mesenchymal proliferation and condensation

The lacrimal gland provides an excellent model with which to study the epithelial-mesenchymal interactions that are crucial to the process of branching morphogenesis. In the current study, we show that bone morphogenetic protein 7 (Bmp7) is expressed with a complex pattern in the developing gland and has an important role in regulating branching. In loss-of-function analyses, we find that Bmp7-null mice have distinctive reductions in lacrimal gland branch number, and that inhibition of Bmp activity in gland explant cultures has a very similar consequence. Consistent with this, exposure of whole-gland explants to recombinant Bmp7 results in increased branch number. In determining which cells of the gland respond directly to Bmp7, we have tested isolated mesenchyme and epithelium. We find that, as expected, Bmp4 can suppress bud extension in isolated epithelium stimulated by Fgf10, but interestingly, Bmp7 has no discernible effect. Bmp7 does, however, stimulate a distinct response in mesenchymal cells. This manifests as a promotion of cell division and formation of aggregates, and upregulation of cadherin adhesion molecules, the junctional protein connexin 43 and of alpha-smooth muscle actin. These data suggest that in this branching system, mesenchyme is the primary target of Bmp7 and that formation of mesenchymal condensations characteristic of signaling centers may be enhanced by Bmp7. Based on the activity of Bmp7 in promoting branching, we also propose a model suggesting that a discrete region of Bmp7-expressing head mesenchyme may be crucial in determining the location of the exorbital lobe of the gland.     

Conformationally restricted analogs of deoxynegamycin

Deoxynegamycin (1b) is a protein synthesis inhibitor with activity against Gram-negative (GN) bacteria. A series of conformationally restricted analogs were synthesized to probe its bioactive conformation. Indeed, some of the constrained analogs were found to be equal or better than deoxynegamycin in protein synthesis assay (1b, IC(50)=8.2 microM; 44, IC(50)=6.6 microM; 35e(2), IC(50)=1 microM). However, deoxynegamycin had the best in vitro whole cell antibacterial activity (Escherichia coli, MIC=4-16 microg/mL; Klebsiella pneumoniae, MIC=8 microg/mL) suggesting that other factors such as permeation may also be contributing to the overall whole cell activity. A new finding is that deoxynegamycin is efficacious in an E. coli murine septicemia model (ED(50)=4.8 mg/kg), providing further evidence of the favorable in vivo properties of this class of molecules.     

Ex vivo and in vivo biological effects of a truncated form of the receptor tyrosine kinase stk when activated by interaction with the friend spleen focus-forming virus envelope glycoprotein or by point mutation

The erythroleukemia-inducing Friend spleen focus-forming virus (SFFV) encodes a unique envelope protein, gp55, which interacts with the erythropoietin (Epo) receptor complex, causing proliferation and differentiation of erythroid cells in the absence of Epo. Susceptibility to SFFV-induced erythroleukemia is conferred by the Fv-2 gene, which encodes a short form of the receptor tyrosine kinase Stk/Ron (sf-Stk) only in susceptible strains of mice. We recently demonstrated that sf-Stk becomes activated by forming a strong interaction with SFFV gp55. To examine the biological consequences of activated sf-Stk on erythroid cell growth, we prepared retroviral vectors which express sf-Stk, either in conjunction with gp55 or alone in a constitutively activated mutant form, and tested them for their ability to induce Epo-independent erythroid colonies ex vivo and disease in mice. Our data indicate that both gp55-activated sf-Stk and the constitutively activated mutant of sf-Stk induce erythroid cells from Fv-2-susceptible and Fv-2-resistant (sf-Stk null) mice to form Epo-independent colonies. Mutational analysis of sf-Stk indicated that a functional kinase domain and 8 of its 12 tyrosine residues are required for the induction of Epo-independent colonies. Further studies demonstrated that coexpression of SFFV gp55 with sf-Stk significantly extends the half-life of the kinase. When injected into Fv-2-resistant mice, neither the gp55-activated sf-Stk nor the constitutively activated mutant caused erythroleukemia. Surprisingly, both Fv-2-susceptible and -resistant mice injected with the gp55-sf-Stk vector developed clinical signs not previously associated with SFFV-induced disease. We conclude that sf-Stk, activated by either point mutation or interaction with SFFV gp55, is sufficient to induce Epo-independent erythroid colonies from both Fv-2-susceptible and -resistant mice but is unable to cause erythroleukemia in Fv-2-resistant mice.     

Preterm birth makes the immature intestine sensitive to feeding-induced intestinal atrophy

Preterm birth and formula feeding predispose to small intestinal dysfunction, which may lead to necrotizing enterocolitis (NEC). In piglets, we tested whether the physiological and environmental transitions occurring at birth affect the response of the immature intestine to enteral feeding. Pig fetuses (106 days gestation, term = 115 days) were prepared with esophageal feeding tubes and fed either sow's colostrum (n = 8) or infant formula (n = 7) in utero. After 24 h of oral feeding, the pig fetuses were delivered by cesarean section and their gastrointestinal morphology and function were compared with those of preterm newborn (NB) littermates that were not fed (n = 8) or fed colostrum (n = 7) or formula (n = 13) for 24 h after birth. Before birth, both colostrum and formula feeding resulted in marked increases in intestinal mass, brush-border enzyme activities, and plasma glucagon-like peptide 2 concentrations, to levels similar to those in NB colostrum-fed piglets. In contrast, NB formula-fed piglets showed reduced intestinal growth, decreased brush-border enzyme activities, and intestinal lesions, reflecting NEC. NB formula-fed pigs also showed impaired enterocyte endocytotic function and decreased antioxidative capacity, whereas brush-border enzyme mRNA levels were unaltered, relative to NB colostrum-fed pigs. Our results indicate that the feeding-induced growth and enzyme maturation of the immature intestine are not birth dependent. However, with a suboptimal diet (milk formula), factors related to preterm birth (e.g., microbial colonization and metabolic and endocrine changes) make the immature intestine sensitive to atrophy and development of NEC.     

Lamins A and C are differentially dysfunctional in autosomal dominant Emery-Dreifuss muscular dystrophy

Mutations in the LMNA gene, which encodes nuclear lamins A and C by alternative splicing, can give rise to Emery-Dreifuss muscular dystrophy. The mechanism by which lamins A and C separately contribute to this molecular phenotype is unknown. To address this question we examined ten LMNA mutations exogenously expressed as lamins A and C in COS-7 cells. Eight of the mutations when expressed in lamin A, exhibited a range of nuclear mislocalisation patterns. However, two mutations (T150P and delQ355) almost completely relocated exogenous lamin A from the nuclear envelope to the cytoplasm, disrupted nuclear envelope reassembly following cell division and altered the protein composition of the mid-body. In contrast, exogenously expressed DsRed2-tagged mutant lamin C constructs were only inserted into the nuclear lamina if co-expressed with any EGFP-tagged lamin A construct, except with one carrying the T150P mutation. The T150P, R527P and L530P mutations reduced the ability of lamin A, but not lamin C from binding to emerin. These data identify specific functional roles for the emerin-lamin C- and emerin-lamin A- containing protein complexes and is the first report to suggest that the A-type lamin mutations may be differentially dysfunctional for the same LMNA mutation.