Chemical lead optimization of a pan Gq mAChR M1, M3, M5 positive allosteric modulator (PAM) lead. Part I: Development of the first highly selective M5 PAM

This Letter describes a chemical lead optimization campaign directed at VU0238429, the first M₅-preferring positive allosteric modulator (PAM), discovered through analog work around VU0119498, a pan G_q mAChR M₁, M₃, M₅ PAM. An iterative library synthesis approach delivered the first selective M₅ PAM (no activity at M₁–M₄ @ 30 μM), and an important tool compound to study the role of M₅ in the CNS.     

Molecular mapping of the thrombin-heparin cofactor II complex

We used 55 Ala-scanned recombinant thrombin molecules to define residues important for inhibition by the serine protease inhibitor (serpin) heparin cofactor II (HCII) in the absence and presence of glycosaminoglycans. We verified the importance of numerous basic residues in anion-binding exosite-1 (exosite-1) and found 4 additional residues, Gln24, Lys65, His66, and Tyr71 (using the thrombin numbering system), that were resistant to HCII inhibition with and without glycosaminoglycans. Inhibition rate constants for these exosite-1 (Q24A, K65A, H66A, Y71A) thrombin mutants (0.02-0.38 x 10(8) m(-1) min(-1) for HCII-heparin when compared with 2.36 x 10(8) m(-1) min(-1) with wild-type thrombin and 0.03-0.53 x 10(8) m(-1) min(-1) for HCII-dermatan sulfate when compared with 5.23 x 10(8) m(-1) min(-1) with wild-type thrombin) confirmed that the structural integrity of thrombin exosite-1 is critical for optimal HCII-thrombin interactions in the presence of glycosaminoglycans. However, our results are also consistent for HCII-glycosaminoglycan-thrombin ternary complex formation. Ten residues surrounding the active site of thrombin were implicated in HCII interactions. Four mutants (Asp51, Lys52, Lys145/Thr147/Trp148, Asp234) showed normal increased rates of inhibition by HCII-glycosaminoglycans, whereas four mutants (Trp50, Glu202, Glu229, Arg233) remained resistant to inhibition by HCII with glycosaminoglycans. Using 11 exosite-2 thrombin mutants with 20 different mutated residues, we saw no major perturbations of HCII-glycosaminoglycan inhibition reactions. Collectively, our results support a "double bridge" mechanism for HCII inhibition of thrombin in the presence of glycosaminoglycans, which relies in part on ternary complex formation but is primarily dominated by an allosteric process involving contact of the "hirudin-like" domain of HCII with thrombin exosite-1.     

Concentrations of nitric oxide in equine preovulatory follicles before and after administration of human chorionic gonadotropin

In the present study, follicular fluids of estrous mares treated with saline solution (Control) or nitric oxide synthase (NOS) inhibitors were analyzed for nitric oxide (NO), estradiol-17beta (E2) and progesterone (P4) concentrations before and 36h after administration of human chorionic gonadotropin (hCG). Follicular fluids obtained before (0h) hCG administration from control mares had lower concentrations of NO than those obtained 36h after administration of hCG (58.3+/-17.8 micromol versus 340.4+/-57.7 micromol; P<0.05). A similar pattern was also noted for intrafollicular P4 in control mares, which had lower concentrations of intrafollicular P4 before hCG than 36h post-hCG administration (P<0.05). As expected, E2 concentrations of control follicles sampled before hCG administration were higher than those sampled 36h post-hCG administration (P<0.05). However, the E2 concentrations in follicles of mares treated with the NOS inhibitors N(omega)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine (AG) did not decrease after hCG administration, unlike those in control mares (P>0.10). In addition, mares treated with NOS inhibitors had lower intrafollicular concentrations of NO and P4 than control mares, both before and after hCG administration (P<0.05). Increased intrafollicular concentrations of NO in control, hCG-stimulated mares provide evidence for the presence of an NO-generating system in the equine preovulatory follicle that is likely upregulated following administration of hCG.     

Pyrene and Phenanthrene Influence on Soil Microbial Populations

Two studies were conducted to evaluate microbial populations in polycyclic aromatic hydrocarbon-contaminated soil. Captina silt loam was freshly exposed to (1) 0 or 2000?mg pyrene/kg and sampled after 10- and 61-wk incubation and (2) 0 or 505?mg pyrene + 445?mg phenanthrene/kg and sampled after a 21-wk incubation. Microbial numbers were determined by plate-count techniques. Isolated bacteria, selected degraders, and wholesoil extracts were analyzed by fatty acid methyl ester analysis (FAME). In the pyrene experiment, pyrene did not affect total bacterial or fungal numbers, but pyrene degraders increased from undetectable levels to 7.09 log₁₀ degraders/g in the contaminated soil. The FAME analysis of bacterial isolates detected no pyrene effect, but wholesoil FAME indicated an increase in the contaminated soil of a fatty acid characteristic of protozoa and a major fatty acid detected in isolated degraders. In the pyrene + phenanthrene experiment, the contaminants had no impact on bacterial, fungal, or actinomycete numbers but increased degrader numbers. No effect of pyrene + phenanthrene was detected by isolate FAME, but whole-soil FAME indicated an effect similar to that in the pyrene experiment. The results indicate that pyrene, although not impacting microbial numbers, may have altered the soil microbial composition and that Captina silt loam can develop an effective degrader population under tested conditions.     

Synthesis of the stationary-phase sigma factor sigma s is positively regulated by ppGpp.

Strains of Escherichia coli which lack detectable guanosine 3',5'-bispyrophosphate (ppGpp) display a pleiotropic phenotype that in some respects resembles that of rpoS (katF) mutants. This led us to examine whether ppGpp is a positive regulator of sigma s synthesis. sigma s is a stationary-phase-specific sigma factor that is encoded by the rpoS gene. We found that a ppGpp-deficient strain is defective in sigma s synthesis as cells enter stationary phase in a rich medium, as judged by immunoblots. Under more-defined conditions we found that the stimulation of sigma s synthesis following glucose, phosphate, or amino acid starvation of wild-type strains is greatly reduced in a strain lacking ppGpp. The failure of ppGpp-deficient strains to synthesize sigma s in response to these starvation regimens could indicate a general defect in gene expression rather than a specific dependence of rpoS expression on ppGpp. We therefore tested the effect of artificially elevated ppGpp levels on sigma s synthesis either with mutations that impair ppGpp decay or by gratuitously inducing ppGpp synthesis with a Ptac::relA fusion. In both instances, we observed enhanced sigma s synthesis. Apparently, ppGpp can activate sigma s synthesis under conditions of nutrient sufficiency as well as during entry into stationary phase. This finding suggests that changes in ppGpp levels function both as a signal of imminent stationary phase and as a signal of perturbations in steady-state growth.     

Epitope Mapping of Form-Specific and Nonspecific Antibodies to Acetylcholinesterase

We have mapped the epitopes to which two monoclonal antibodies against acetylcholinesterase (AChE) from Torpedo californica are directed. One antibody, 2C9, has equivalent affinity for both the 5.6S (amphiphilic) and 11S (hydrophilic) enzyme forms; the other, 4E7, recognizes only the amphiphilic form and has been shown previously to require an N-linked oligosaccharide residue on the protein. Isolation of cyanogen bromide peptides from the amphiphilic form and assay by a competition ELISA for 2C9 and by a direct binding ELISA for 4E7 identified the same peptide, residues 44–82, as containing epitopes against both antibodies. The epitope for 4E7 includes the oligosaccharide conjugated to Asp⁵⁹, an N-linked glycosylation site not present in mouse AChE. A 20-amino-acid synthetic peptide, RFRRPEPKKPWSQVWNASTY, representing residues 44–63, was synthesized and found to inhibit completely 2C9 binding to 5.6S enzyme at molar concentrations comparable to those of the cyanogen bromide peptide. It was unreactive with 4E7. Fractionation of the synthetic peptide further localized the 2C9 epitope. Peptides RFRRPEPKKPW and KPWSGVWNASTY both reacted but less so than the entire synthetic peptide at equivalent molar concentrations, whereas the peptide RPEPKKPWSGVWNASTY was as effective as the larger synthetic peptide. The crystal structure of AChE shows the peptide to be on the surface of the molecule as part of a convex hairpin loop starting before the first α-helix.     

Characterization of the binding of transforming growth factor-beta 1, -beta 2, and -beta 3 to recombinant beta 1-latency-associated peptide.

Preprotransforming growth factor-beta 1 (TGF beta 1) is a 390-amino acid precursor polypeptide that undergoes a number of processing steps to yield mature TGF beta 1 (amino acid residues 279-390) and a pro portion (residues 30-278) termed beta 1-latency-associated peptide (beta 1LAP). The dimeric form of beta 1LAP has been shown to associate noncovalently with the mature growth factor, resulting in inactivation of biological activity. To further characterize this interaction, the mature TGF beta 1 was radioiodinated and used to determine dissociation constants. A cross-linking method using the bifunctional covalent cross-linker bis-(sulfosuccinimidyl)suberate was found to be the best approach for measuring the amount of bound growth factor. The efficiency of cross-linking was constant within each experiment and varied between 45-55%. Saturation plots and their associated Scatchard analyses indicate apparent Kd values between 1.1-1.8 nM. Competition of TGF beta 1 binding to beta 1LAP by TGF beta 2 and TGF beta 3 (two closely related growth factors) revealed that the latter also bind beta 1LAP tightly, with apparent Kd values of 1.9 and 0.4 nM, respectively.     

Thrombospondin and vascular endothelial growth factor are cyclically expressed in an inverse pattern during bovine ovarian follicle development

Angiogenesis does not normally occur in most adult tissues. However, in the ovary, there are cyclical vascular changes including angiogenesis that involve the interaction of numerous cytokines and growth factors. Angiogenic processes are regulated by a balance between pro- and antiangiogenic factors. The purpose of this study was to determine the expression of the antiangiogenic thrombospondin family and proangiogenic vascular endothelial growth factor (VEGF) in various sizes of healthy bovine follicles. Ovaries were collected from slaughterhouse animals and healthy follicles were sorted based on size (< 0.5 cm, small; 0.5-1.0 cm, medium; >1.0 cm, large). Thrombospondin (TSP) protein levels were significantly higher in small follicles. Immunohistochemistry confirmed the granulosa layer as the primary area within the follicle involved in TSP generation and that small follicles had the highest proportion of immunopositive cells. TSP-1 and -2 mRNA levels were significantly higher in small follicles than either medium or large follicles. TSP colocalized with CD36 on granulosa cells (GC) in the follicle and in cultured cells. In contrast with TSP, VEGF expression increased during growth and development of the follicle. FSH stimulated GC expression of TSP, while LH had no effect. In summary, TSP-1 and -2 were coordinately expressed in the extravascular compartment of the ovary during early follicle development. VEGF was inversely expressed, with expression increasing as follicles developed. Regulated expression and localization of these proteins suggests that they may be involved in regulating growth and development of the follicle in a novel fashion.     

The rel gene is essential for in vitro growth of Staphylococcus aureus

The stringent response in Staphylococcus aureus is mediated by the nucleotide guanosine pentaphosphate, whose synthesis is catalyzed by the product of the rel gene. We report here that the rel gene is essential for the in vitro growth of S. aureus, distinguishing it from all other bacteria tested for this requirement.