Identification and characterization of new inhibitors of the Escherichia coli MurA enzyme.

The bacterial enzyme MurA catalyzes the transfer of enolpyruvate from phosphoenolpyruvate (PEP) to uridine diphospho-N-acetylglucosamine (UNAG), which is the first committed step of bacterial cell wall biosynthesis. From high-throughput screening of a chemical library, three novel inhibitors of the Escherichia coli MurA enzyme were identified: the cyclic disulfide RWJ-3981, the purine analog RWJ-140998, and the pyrazolopyrimidine RWJ-110192. When MurA was preincubated with inhibitor, followed by addition of UNAG and PEP, the 50% inhibitory concentrations (IC(50)s) were 0.2 to 0.9 microM, compared to 8.8 microM for the known MurA inhibitor, fosfomycin. The three compounds exhibited MICs of 4 to 32 microg/ml against Staphylococcus aureus; however, the inhibition of DNA, RNA, and protein synthesis in addition to peptidoglycan synthesis by all three inhibitors indicated that antibacterial activity was not due specifically to MurA inhibition. The presence of UNAG during the MurA and inhibitor preincubation lowered the IC(50) at least fivefold, suggesting that, like fosfomycin, the three compounds may interact with the enzyme in a specific fashion that is enhanced by UNAG. Ultrafiltration and mass spectrometry experiments suggested that the compounds were tightly, but not covalently, associated with MurA. Molecular modeling studies demonstrated that the compounds could fit into the site occupied by fosfomycin; exposure of MurA to each compound reduced the labeling of MurA by tritiated fosfomycin. Taken together, the evidence indicates that these inhibitors may bind noncovalently to the MurA enzyme, at or near the site where fosfomycin binds.

Characterization of the Epha1 receptor tyrosine kinase: expression in epithelial tissues.

The Eph family of receptor tyrosine kinases plays a crucial role during development and is implicated in oncogenesis. Using a partial cDNA clone of an Eph-related kinase (Esk) we isolated the complete coding region of a gene which we show to be murine EphA1 by both structural and functional criteria. The chromosomal localization is shown to be syntenic to hEphA1 and the genomic organization also shows distinct features found in the hEphA1 gene. Functionally, in keeping with findings for the human homologue, both soluble recombinant and "native" mEphA1 show preferential binding to ephrin A1. However, we also observed significant binding to other A-type ligands as has been observed for other Eph receptors. We analysed the expression of mEphA1 mRNA by in situ hybridization on tissue sections. mEphA1 was expressed in epithelial elements of skin, adult thymus, kidney and adrenal cortex. Taken together with previous Northern blotting data these results suggest that mEphA1 is expressed widely in differentiated epithelial cells.

Amidino benzimidazole inhibitors of bacterial two-component systems.

Amidino benzimidazoles have been identified as inhibitors of the bacterial KinA/Spo0F two-component system (TCS). Many of these inhibitors exhibit good in vitro antibacterial activity against a variety of susceptible and resistant Gram-positive organisms. The moiety at the 2-position of the benzimidazole was extensively modified. In addition, the regioisomeric benzoxazoles, heterocyclic replacements for the benzimidazole, have been synthesized and their activity against the TCS evaluated.

Organization and chromosomal localization of the murine Testisin gene encoding a serine protease temporally expressed during spermatogenesis.

The recently characterized human serine protease, Testisin, is expressed on premeiotic testicular germ cells and is a candidate type II tumor suppressor for testicular cancer. Here we report the cloning, characterization and expression of the gene encoding mouse Testisin, Prss21. The murine Testisin gene comprises six exons and five introns and spans approximately 5 kb of genomic DNA with an almost identical structure to the human Testisin gene, PRSS21. The gene was localized to murine chromosome 17 A3.3-B; a region syntenic with the location of PRSS21 on human chromosome 16p13.3. Northern blot analyses of RNA from a range of adult murine tissues demonstrated a 1.3 kb mRNA transcript present only in testis. The murine Testisin cDNA shares 65% identity with human Testisin cDNA and encodes a putative pre-pro-protein of 324 amino acids with 80% similarity to human Testisin. The predicted amino-acid sequence includes an N-terminal signal sequence of 27 amino acids, a 27 amino-acid pro-region, a 251 amino-acid catalytic domain typical of a serine protease with trypsin-like specificity, and a C-terminal hydrophobic extension which is predicted to function as a membrane anchor. Immunostaining for murine Testisin in mouse testis demonstrated specific staining in the cytoplasm and on the plasma membrane of round and elongating spermatids. Examination of murine Testisin mRNA expression in developing sperm confirmed that the onset of murine Testisin mRNA expression occurred at approximately day 18 after birth, corresponding to the appearance of spermatids in the testis, in contrast to the expression of human Testisin in spermatocytes. These data identify the murine ortholog to human Testisin and demonstrate that the murine Testisin gene is temporally regulated during murine spermatogenesis.

Gene structure alternative splicing, and chromosomal localization of pro-apoptotic Bcl-2 relative Bim.

Bim is a proapoptotic protein of the Bcl-2 family that shares only the short BH3 domain with other members. It has three isoforms, apparently produced by alternative splicing. The demonstration that Bim is essential for certain apoptotic responses and to prevent overproduction of hematopoietic cells suggests that it may be a tumor suppressor. We have, therefore, investigated the organization of the mouse Bim gene, delineating its promoter and splicing, and positioned the gene on both mouse and human chromosomes. Bim has six exons, but the third is a facultative intron that is spliced out in the mRNAs for the smaller isoforms (BimL and BimS), but not that encoding the largest isoform (BimEL). The 0.8-kb region 5' to exon 1, which contains a TATA-less promoter and binding sites for several transcription factors, can drive expression of a reporter gene. Mouse Bim localizes to the distal third of Chromosome (Chr) 2, near the F-G boundary, and its human counterpart to Chr 2q12 or q13. Deletions of these bands have been reported in ten tumors (eight hematopoietic), reinforcing the possibility that Bim is a tumor suppressor. These findings should help to clarify the regulation of Bim expression and to assess whether mutations involving Bim contribute to neoplastic and other diseases.

An orphaned mammalian beta-globin gene of ancient evolutionary origin.

Mammals possess multiple, closely linked beta-globin genes that differ in the timing of their expression during development. These genes have been thought to be derived from a single ancestral gene, by duplication events that occurred after the separation of the mammals and birds. We report the isolation and characterization of an atypical beta-like globin gene (omega-globin) in marsupials that appears to be more closely related to avian beta-globin genes than to other mammalian beta-globin genes, including those previously identified in marsupials. Phylogenetic analyses indicate that omega-globin evolved from an ancient gene duplication event that occurred before the divergence of mammals and birds. Furthermore, we show that omega-globin is unlinked to the previously characterized beta-globin gene cluster of marsupials, making this the first report of an orphaned beta-like globin gene expressed in a vertebrate.

Cloning of leptin cDNA and assignment to the long arm of chromosome 5 in the marsupial Sminthopsis crassicaudata.

We have isolated and sequenced full-length cDNA clones for leptin in the dasyurid marsupial Sminthopsis crassicaudata (fat-tailed dunnart). Southern and in situ hybridisation data indicated a single leptin gene in the S. crassicauda- ta genome, localised to arbitrary chromosome bands 5q24--> q31 on the long arm of chromosome 5, the short-arm terminus of which bears the only nucleolar organising region. The nucleotide sequence of the cDNAs revealed that the primary translation product of S. crassicaudata leptin is composed of 167 amino acid residues, with a potential signal peptide of 21 residues. The mature protein of 146 amino acids is 82% similar to both the mouse and human proteins and is predicted to have a molecular weight of 16.26 kDa. Northern blot analysis revealed that the corresponding mRNA is approximately 3.9 kb in size and is expressed only in white adipose tissue of this marsupial species. Evolutionary analyses indicate that S. crassicaudata leptin cDNA has evolved at a significantly faster rate than cDNAs from eutherian mammals.

Expression profiling of pancreatic beta cells: glucose regulation of secretory and metabolic pathway genes.

Pancreatic beta cells respond to changes in blood glucose by secreting insulin and increasing insulin synthesis. To identify genes used in these responses, we have carried out expression profiling of beta cells exposed to high (25 mM) or low (5.5 mM) glucose by using oligonucleotide microarrays. Functional clustering of genes that averaged a 2.2-fold or greater change revealed large groups of secretory pathway components, enzymes of intermediary metabolism, cell-signaling components, and transcription factors. Many secretory pathway genes were up-regulated in high glucose, including seven members of the endoplasmic reticulum (ER) translocon. In agreement with array analysis, protein levels of translocon components were increased by high glucose. Most dramatically, the alpha subunit of the signal recognition particle receptor was increased over 20-fold. These data indicate that the translocon and ribosome docking are major regulatory targets of glucose in the beta cell. Analysis of genes encoding enzymes of intermediary metabolism indicated that low glucose brought about greater utilization of amino acids as an energy source. This conclusion was supported by observations of increased urea production under low-glucose conditions. The above results demonstrate genome-wide integration of beta-cell functions at the level of transcript abundance and validate the efficacy of expression profiling in identifying genes involved in the beta-cell glucose response.

Solh, the mouse homologue of the Drosophila melanogaster small optic lobes gene: organization, chromosomal mapping, and localization of gene product to the olfactory bulb.

The Drosophila melanogaster small optic lobes gene (sol) is required for normal development of the neuropiles of the medulla and lobula complexes of the adult optic lobes. The predicted protein products of sol and its human homologue SOLH contain zinc-finger-like repeats, a calpain-like protease domain, and a C-terminal domain of unknown function. Long-distance PCR was used to amplify genomic DNA for Solh, the mouse homologue of sol, following the identification of mouse Solh expressed sequence tags. The nucleotide sequence of the Solh coding region (6.0 kb) was determined. The predicted Solh protein of 1095 amino acid residues shows 89% identity (93% similarity) to the human homologue. Solh was localized by in situ hybridization to band A3.3 on mouse Chromosome 17, in a region of maintained homology with human 16p13.3. Antipeptide antibodies were prepared and verified by demonstration of specific reactivity with recombinant human SOLH protein prepared by in vitro transcription/translation and expression in insect cells using the baculovirus system. The antibodies were used to show that the Solh protein localizes to the olfactory bulb in mouse and rat brain, suggesting that it could have an analogous role in development of sensory system neurons in Drosophila and in mammals.

Genomic characterization of the sheep vasopressin V1a receptor gene and promoter, with assignment to bands q23-24 of sheep chromosome 3 and cattle chromosome 5.

Arginine vasopressin interacts with the vasopressin type 1a receptor (V1aR) to initiate physiological effects such as vasoconstriction of blood vessels and glycogenolysis. AVP is also involved in central nervous effects such as body homeostasis and blood pressure control. The complete genomic organization of the sheep V1aR gene has been determined, including the presence of one major and two minor transcriptional start sites at -321, -206 and -91bp respectively, relative to the ATG codon. Another more distal minor transcriptional start site was also localized between nucleotides -997 and -892 relative to the ATG codon. One intron exists in the sheep V1aR gene and potential cis- and trans- acting sites were identified in the sheep V1aR promoter. The promoter was also compared to the rat V1aR promoter. The sheep V1aR promoter displays features typical of housekeeping genes, although tissue-specific expression does not support this. V1aR mRNA is absent in the adult sheep liver but not the kidney. One copy of the V1aR gene exists in the sheep genome, which was localized to chromosome 3q23-24, and to the homoeologous position, 5q23-24 in cattle.

SOLH, a human homologue of the Drosophila melanogaster small optic lobes gene is a member of the calpain and zinc-finger gene families and maps to human chromosome 16p13.3 near CATM (cataract with microphthalmia).

Mutations in the Drosophila melanogaster small optic lobes (sol) gene cause a sever reduction in the neuropiles of the medulla and lobula complexes of the adult optic lobes. The predicted protein product of sol contains zinc-finger-like repeats, a calpain-like protease domain, and a C-terminal region of unknown function. We have isolated human brain cDNA for SOLH, a human homologue of sol. The human SOLH gene consists of 14 exons distributed over more than 45 kb of genomic DNA. The encoded SOLH protein of 1086 amino acids has strong similarity to the D. melanogaster protein. The calpain-like domain and C-terminal region are highly conserved (58% identity), and similar Cys2-Cys2 zinc fingers are present in the N-terminal region. A reported Caenorhabditis elegans homologue contains the calpain domain and C-terminal region, but appears to lack the zinc finger region. A single copy of the zinc finger sequence is present in adjacent C. elegans genomic cosmid DNA sequence, and we show that it is part of the C. elegans sol-like transcript. Northern analysis of human tissues revealed a SOLH transcript of approximately 5 kb that was strongest in human brain. We have mapped the SOLH gene to chromosome 16p13.3 by in situ hybridization. SOLH is a candidate gene for CATM (hereditary cataracts with microphthalmia), which maps in this region.

Substituted salicylanilides as inhibitors of two-component regulatory systems in bacteria.

A new class of inhibitors of the two-component regulatory systems (TCS) of bacteria was discovered based on the salicylanilide screening hits, closantel (1) and tetrachlorosalicylanilide (9). A systematic SAR study versus a model TCS, KinA/Spo0F, demonstrated the importance of electron-attracting substituents in the salicyloyl ring and hydrophobic groups in the anilide moiety for optimal activity. In addition, derivatives 8 and 16, containing the 2, 3-dihydroxybenzanilide structural motif, were potent inhibitors of the autophosphorylation of the KinA kinase, with IC50s of 2.8 and 6. 3 µM, respectively. Compound 8 also inhibited the TCS mediating vancomycin resistance (VanS/VanR) in a genetically engineered Enterococcus faecalis cell line at concentrations subinhibitory for growth. Closantel (1), tetrachlorosalicylanilide (9), and several related derivatives (2, 7, 10, 11, 20) had antibacterial activity against the drug-resistant organisms, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VREF).

Novel inhibitors of bacterial two-component systems with gram positive antibacterial activity: pharmacophore identification based on the screening hit closantel.

This SAR study has shown that the salicylanilide is the pharmacophore for inhibition of the bacterial two-component system. Hydrophobic substituents improve the potency of inhibitors in this series; however, hydrophobicity is not the sole determinant for inhibition; structural and electronic requirements also exist. Closantel (1) was found to inhibit a two-component system and to have antibacterial activity against drug resistant S. aureus and E. faecium.

SAR studies of diaryltriazoles against bacterial two-component regulatory systems and their antibacterial activities.

A series of diaryltriazole analogs was discovered to inhibit bacterial two-component regulatory systems in our primary assays, KinA/Spo0F and NRII/NRI. They also showed inhibitory activity in whole cell mechanism-based assays, and they possessed potent activities against several strains of Gram-positive pathogenic bacteria in the standard MIC broth assay.