Characterization of the structural forces governing the reversibility of the thermal unfolding of the human acidic fibroblast growth factor

Overexpression and biophysical and functional characterization of a recombinant FGF21

Fibroblast growth factor 21 (FGF21) is an endocrine FGF that plays a vital role in regulating essential metabolic pathways. FGF21 increases glucose uptake by cells, promotes fatty acid oxidation, reduces blood glucose levels, and alleviates metabolic diseases. However, detailed studies on its stability and biophysical characteristics have not been reported. Herein, we present the overexpression, biophysical characterization, and metabolic activity of a soluble recombinant FGF21 (rFGF21). The far-UV circular dichroism spectra of rFGF21 show a negative trough at 215 nm, indicating that the protein's backbone predominantly adopts a β sheet conformation. rFGF21 shows intrinsic tyrosine fluorescence at 305 nm. Thermal denaturation using differential scanning calorimetry reveals that rFGF21 is relatively thermally unstable, with a melting temperature of 46.8°C (±0.1°C). The urea-induced unfolding of rFGF21 is rapid, with a chemical transition midpoint of 0.4 M. rFGF21 is readily cleaved by trypsin in limited trypsin digestion assays. Isothermal titration calorimetry experiments show that rFGF21 does not bind to heparin. Interestingly, rFGF21 demonstrates proliferative activity in NIH/3T3 fibroblasts and enhances mitochondrial oxidative phosphorylation and fatty acid oxidation in 3T3-L1 adipocytes. These findings provide a crucial framework for the engineering of novel structure-based variants of FGF21 with improved stability and biological activity to treat metabolic disorders.

Understanding Folding of bFGF and Potential Cellular Protective Mechanisms of Neural Cells

Traumatic brain injury (TBI) is a serious health condition that affects an increasing number of people, especially veterans and athletes. TBI causes serious consequences because of its long-lasting impact on the brain and its alarming frequency of occurrence. Although the brain has some natural protective mechanisms, the processes that trigger them are poorly understood. Fibroblast growth factor (FGF) proteins interact with receptor proteins to protect cells. Gaps in the literature include how basic-FGF (bFGF) is activated by heparin, can heparin-like molecules induce neural protection, and the effect of allosteric binding on bFGF activity. To fill the gap in our understanding, we applied temperature replica exchange to study the influence of heparin binding to bFGF and how mutations in bFGF influence stability. A new favorable binding site was identified by comparing free energies computed from the potential of mean force (PMF). Although the varied sugars studied resulted in different interactions with bFGF compared to heparin, they each produced structural effects similar to those of bFGF that likely facilitate receptor binding and signaling. Our results also demonstrate how point mutations can trigger the same conformational change that is believed to promote favorable interactions with the receptor. A deeper atomic-level understanding of how chemicals are released during TBI is needed to improve the development of new treatments for TBI and could contribute to a better understanding of other diseases.

Quantitative and qualitative differences in the activation of a fibroblast growth factor receptor by different FGF ligands

The FGF system is the most complex of all receptor tyrosine kinase signaling networks with 18 FGF ligands and four FGFRs that deliver morphogenic signals to pattern most embryonic structures. Even when a single FGFR is expressed in the tissue, different FGFs can trigger dramatically different biological responses via this receptor. Here we show both quantitative and qualitative differences in the signaling of one of the FGF receptors, FGFR1c, in response to different FGFs. We provide an overview of the recent discovery that FGFs engage in biased signaling via FGFR1c. We discuss the concept of ligand bias, which represents qualitative differences in signaling as it is a measure of differential ligand preferences for different downstream responses. We show how FGF ligand bias manifests in functional data in cultured chondrocyte cells. We argue that FGF-ligand bias contributes substantially to FGF-driven developmental processes, along with known differences in FGF expression levels, FGF-FGFR binding coefficients and differences in FGF stability in vivo.

Unraveling the binding mechanisms of transglutaminase and substrate subjected to microwaves: Molecular docking and molecular dynamic simulations

Previous studies showed that transglutaminase (TGase) and microwaves acted synergistically to improve the functional properties of proteins. The mechanism behind this has yet to be elucidated. In this study, the phenomenon of microwaves enhancing TGase activity was experimentally validated. Molecular docking and molecular dynamics simulations revealed that moderate microwaves (105 and 108 V/m) increased the structural flexibility of TGase and promoted the orientation of the side chain carboxylate anion group on Asp255, driving the reaction forward. Also, TGase underwent partial transformation from α-helix to turns or coils at 105 and 108 V/m, exposing more residues in the active site and facilitating the binding of the substrate (CBZ-Gln-Gly) to TGase. However, 109 V/m microwaves completely destroyed the TGase structure, inactivating the enzyme. This study provides insights into the molecular mechanisms underlying the interactions between TGase and substrate subjected to microwaves, promoting the future applications of TGase and microwaves in food processing.

Overexpression and Purification of Mitogenic and Metabolic Fibroblast Growth Factors

Fibroblast growth factors (FGFs) are proteins with a vast array of biological activity, such as cell development and repair, glucose and bile acid metabolisms, and wound healing. Due to their critical and diverse physiological functions, FGFs are believed to possess potential as therapeutic agents for many diseases and conditions that warrant further investigations. Thus, a simple, cost-efficient method to purify these biologically active signaling proteins is desirable. Herein, we introduce such techniques to purify FGFs that possess either high heparin-binding affinity or low to no heparin-binding affinity. This method takes advantage of the high affinity toward heparin sulfate from paracrine FGF1 to isolate the targeted protein. It also accounts for FGF members that have low heparin affinity, such as the metabolic FGFs, by introducing poly-histidine tags in the recombinant protein in combination with the immobilized metal affinity chromatography. Subsequently, the purified FGF products are separated from the other small protein by high-speed centrifugation. Products are then subjected to other biophysical experiments like SDS-PAGE, mass spectrometry, circular dichroism, intrinsic fluorescence, isothermal titration calorimetry, differential scanning calorimetry, and biological cell activity assay to confirm that the target proteins are purified with intact native conformation and no significant change in the intrinsic characteristics and biological activities.

Pharmacology of Heparin and Related Drugs: An Update

Heparin has been used extensively as an antithrombotic and anticoagulant for close to 100 years. This anticoagulant activity is attributed mainly to the pentasaccharide sequence, which potentiates the inhibitory action of antithrombin, a major inhibitor of the coagulation cascade. More recently it has been elucidated that heparin exhibits anti-inflammatory effect via interference of the formation of neutrophil extracellular traps and this may also contribute to heparin's antithrombotic activity. This illustrates that heparin interacts with a broad range of biomolecules, exerting both anticoagulant and nonanticoagulant actions. Since our previous review, there has been an increased interest in these nonanticoagulant effects of heparin, with the beneficial role in patients infected with SARS2-coronavirus a highly topical example. This article provides an update on our previous review with more recent developments and observations made for these novel uses of heparin and an overview of the development status of heparin-based drugs. SIGNIFICANCE STATEMENT: This state-of-the-art review covers recent developments in the use of heparin and heparin-like materials as anticoagulant, now including immunothrombosis observations, and as nonanticoagulant including a role in the treatment of SARS-coronavirus and inflammatory conditions.

Structural insights into inhibition of PRRSV Nsp4 revealed by structure-based virtual screening, molecular dynamics, and MM-PBSA studies

BACKGROUND

Porcine reproductive and respiratory syndrome respiratory sickness in weaned and growing pigs, as well as sow reproductive failure, and its infection is regarded as one of the most serious swine illnesses worldwide. Given the current lack of an effective treatment, in this study, we identified natural compounds capable of inhibiting non-structural protein 4 (Nsp4) of the virus, which is involved in their replication and pathogenesis.

RESULTS

We screened natural compounds (n = 97,999) obtained from the ZINC database against Nsp4 and selected the top 10 compounds for analysing protein-ligand interactions and physicochemical properties. The five compounds demonstrating strong binding affinity were then subjected to molecular dynamics simulations (100 ns) and binding free energy calculations. Based on analysis, we identified four possible lead compounds that represent potentially effective drug-like inhibitors.

CONCLUSIONS

These methods identified that these natural compounds are capable of inhibiting Nsp4 and possibly effective as antiviral therapeutics against PRRSV.