Discovery of small molecule binders of human FSHR(TMD) with novel structural scaffolds by integrating structural bioinformatics and machine learning algorithms

FSHR activation through small molecule modulators: Mechanistic insights from MD simulations

Follicle-stimulating hormone receptor (FSHR) is a glycoprotein hormone receptor that plays a vital role in reproduction, cancer progression and osteoporosis. Owing to its therapeutic importance, several small molecule modulators have been identified by researchers through high throughput studies that usually include virtual screening of chemical libraries followed by in vitro validation through radio-ligand binding assays, cAMP accumulation and luciferase-based luminescence assays. The binding site of these modulators and structural changes that accompany modulator binding remains elusive. Here, we address these aspects through molecular docking and MD simulations on well-studied FSHR modulators and comparing the domain motions between agonist/FSH bound and antagonist bound FSHR structures. It was observed that agonist and antagonist modulators bind to the same site, but interact with distinct residues in transmembrane domain(TMD). FSHR(TMD) residues Ile522, Ala595, Ile602 and Val604 were found to interact only with agonist. Notably, these residues are conserved in the close homolog luteinizing hormone/choriogonadotropin receptor (LHCGR) and participate in interaction with its agonist Org43553. We observed distinctly prominent domain motions and conformational changes in TM helices 3, 4 and 6 for agonist bound FSHR structure. These structural changes have also been reported for LHCGR, and few GPCR members suggesting an important and well conserved mechanism of GPHR activation that could be exploited for design of novel modulators.

Mapping of FSHR agonists and antagonists binding sites to identify potential peptidomimetic modulators

Owing to the critical role of follicle stimulating hormone receptor (FSHR) signaling in human reproduction, FSHR has been widely explored for development of fertility regulators. Using high-throughput screening approaches, several low molecular weight (LMW) compounds that can modulate FSHR activity have been identified. However, the information about the binding sites of these molecules on FSHR is not known. In the present study, we extracted the structural and functional information of 161 experimentally validated LMW FSHR modulators available in PubMed records. The potential FSHR binding sites for these modulators were identified through molecular docking experiments. The binding sites were further mapped to the agonist or antagonist activity reported for these molecules in literature. MD simulations were performed to evaluate the effect of ligand binding on conformational changes in the receptor, specifically the transmembrane domain. A peptidomimetic library was screened using these binding sites. Six peptidomimetics that interacted with the residues of transmembrane domain and extracellular loops were evaluated for binding activity using in vitro cAMP assay. Two of the six peptidomimetics exhibited positive allosteric modulatory activity and four peptidomimetics exhibited negative allosteric modulatory activity. All six peptidomimetics interacted with Asp521 of hFSHR(TMD). Several of the experimentally known LMW FSHR modulators also participated in H-bond interactions with Asp521, suggesting its important role in FSHR modulatory activity.

Compassion fatigue among haemodialysis nurses in public and private hospitals in China

AIM

This study was conducted to identify and compare the levels of compassion fatigue and job satisfaction among haemodialysis nurses in public and private hospitals in China and explore explanatory factors based on sociodemographic and occupational characteristics.

METHODS

A descriptive study was conducted using a self-designed demographic questionnaire, the Professional Quality of Life Scale and the Minnesota Satisfaction Questionnaire, with responses from 283 haemodialysis nurses working at six public and private hospitals in China between June and November 2018.

RESULTS

The compassion fatigue score of public hospital nurses was significantly higher than that of private hospital nurses. Univariate analysis showed that there were significant differences in compassion fatigue among nurses based on the number of years worked, nature of employment, and education level. Correlational analysis showed a negative correlation between overall job satisfaction and compassion fatigue in both public and private hospitals. Multiple regression analysis showed that compassion fatigue among haemodialysis nurses in public hospitals was associated with years worked, type of employment, and intrinsic and extrinsic satisfaction, whereas in private hospitals, education level, years worked, and intrinsic and extrinsic satisfaction were significant.

CONCLUSION

Haemodialysis nurses in public hospitals are more likely to develop compassion fatigue than those in private hospitals.

Drug design targeting active posttranslational modification protein isoforms

Modern drug design aims to discover novel lead compounds with attractable chemical profiles to enable further exploration of the intersection of chemical space and biological space. Identification of small molecules with good ligand efficiency, high activity, and selectivity is crucial toward developing effective and safe drugs. However, the intersection is one of the most challenging tasks in the pharmaceutical industry, as chemical space is almost infinity and continuous, whereas the biological space is very limited and discrete. This bottleneck potentially limits the discovery of molecules with desirable properties for lead optimization. Herein, we present a new direction leveraging posttranslational modification (PTM) protein isoforms target space to inspire drug design termed as "Post-translational Modification Inspired Drug Design (PTMI-DD)." PTMI-DD aims to extend the intersections of chemical space and biological space. We further rationalized and highlighted the importance of PTM protein isoforms and their roles in various diseases and biological functions. We then laid out a few directions to elaborate the PTMI-DD in drug design including discovering covalent binding inhibitors mimicking PTMs, targeting PTM protein isoforms with distinctive binding sites from that of wild-type counterpart, targeting protein-protein interactions involving PTMs, and hijacking protein degeneration by ubiquitination for PTM protein isoforms. These directions will lead to a significant expansion of the biological space and/or increase the tractability of compounds, primarily due to precisely targeting PTM protein isoforms or complexes which are highly relevant to biological functions. Importantly, this new avenue will further enrich the personalized treatment opportunity through precision medicine targeting PTM isoforms.

Identification and in vivo validation of a 9-mer peptide derived from FSHβ with FSHR antagonist activity

FSH-FSHR interaction is critical for folliculogenesis, spermatogenesis and progression of several cancers. Therefore, FSHR is an attractive target for fertility regulation and cancer therapeutics. Based on homology and structural analysis of hFSH-FSHR(ECD) complex, a minimal continuous stretch within FSHβ seat-belt loop (FSHβ (89-97)) was identified to be crucial for FSHR interaction. The ability of FSHβ (89-97) peptide to neutralize FSHR activity was evaluated by a panel of in vitro and in vivo experiments. The synthetic peptide significantly inhibited binding of [¹²⁵I]-FSH to rat Fshr as well as FSH-induced cAMP production. In immature rats, FSHβ (89-97) peptide administration reduced FSH-mediated increase in ovarian weight. The peptide inhibited transition of follicles from pre-antral to antral stage and hindered the cell cycle progression of granulosa cells beyond G0/G1 phase. In adult rats, administration of the peptide inhibited estradiol synthesis and significantly perturbed folliculogenesis.