Solubilization, purification, and ligand binding characterization of G protein-coupled receptor SMO in native membrane bilayer using styrene maleic acid copolymer

Tethering Efficiency of Reversible Addition-Fragmentation Chain Transfer-Synthesized Styrene Maleic Acid Polymers and Associated Styrene Maleic Acid Lipid Nanoparticles on Gold Surfaces

Styrene maleic acid lipid nanoparticles (SMALPs) arise from amphipathic styrene maleic acid (SMA) copolymer encapsulation of membranes into polymer-lipid nanodiscs, structures applied in the native extraction of membrane proteins (MPs). Strategies to immobilize SMALPs via their polymer belt onto surfaces allow the biophysical study of MPs without direct protein-surface anchoring. In this work, reversible addition-fragmentation chain transfer (RAFT) polymerization is used to synthesize a library of diblock SMA copolymers to determine the optimal sequence for SMALP assembly. The further ability of trithiocarbonates (T) and attached (Z)-end-groups, generated by RAFT polymerization, to tether SMALPs to gold surfaces via sulfur-gold bonds is evaluated. Improved DMPC liposome solubilization is achieved with a hydrophilic (Z)-end-group, shorter polystyrene block and lower molecular weight for diblock R-(Sty)-b-(Sty-alt-MA)-T-Z polymers. Quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM) revealed that diblock SMA polymers bound to gold as a micellular film, irrespective of the presence of the trithiocarbonate group. SMALPs, however, showed an enhanced gold affinity when terminated by a trithiocarbonate and hydrophilic RAFT (Z)-end-group compared to end-group removed SMALPs, the latter exhibiting nonspecific gold adhesion. These findings offer a new approach in utilizing RAFT end-groups of nanodisc assembling polymers for label-free analysis of MPs.

Plasma Protein Binding, Biostability, Metabolite Profiling, and CYP450 Phenotype of TPB15 Across Different Species: A Novel Smoothened Inhibitor for TNBC Therapy

Background/Objectives: Triple-negative breast cancer (TNBC) is a major cause of cancer-related deaths among women. The Hedgehog (Hh) signaling pathway plays a critical role in tumor development, and targeting this pathway may provide new therapeutic opportunities for TNBC. TPB15 is a novel smoothened inhibitor of the Hh pathway, showing promising tumor reduction and low-toxicity properties in vivo/vitro. This study aims to evaluate TPB15's protein binding rates, metabolic stability, and metabolism across different species, including mice, rats, dogs, monkeys, and humans. Methods: TPB15 was synthesized, and its pharmacokinetic profile was assessed. Plasma protein binding was determined using ultrafiltration across multiple species. Stability studies were conducted in plasma and liver microsomes from each species. Additionally, metabolic enzymes in human liver microsomes were characterized with selective CYP450 inhibitors, and high-resolution mass spectrometry was employed to identify metabolites. Results: Plasma protein binding of TPB15 was consistent across species, ranging from 81.5% to 82.4% in humans and rats. After 120 min, TPB15 remained stable in plasma, with retention rates of 97.2-98.3%. The elimination half-life (t1/2) varied from 88 min in monkeys to 630 min in dogs. In human liver microsomes, metabolism was significantly inhibited by sulfaphenazole and ketoconazole, indicating the involvement of CYP3A4 and CYP2C9 enzymes. TPB15 underwent phase I metabolism, producing a major metabolite with a molecular weight of 468.9. Conclusions: TPB15 demonstrates stable pharmacokinetic properties across species, with consistent protein binding and significant variability in half-life. The observed differences in metabolism are primarily attributed to CYP2C9 and CYP3A4, offering valuable insights into its drug development potential.

The application of nanodiscs in membrane protein drug discovery & development and drug delivery

The phospholipid bilayer nanodiscs (LNDs), as a rapidly-developing tool in recent years, provide a natural bio-memebrane environment to maintain the native conformation and functions of membrane proteins as well as a versatile delivery vehicle for a variety of hydrophobic and hydrophilic drugs. We have seen unprecedented advantages of phospholipid bilayer nanodiscs in membrane protein structure characterization, biochemical and physiological studies of membrane proteins, membrane environment studies, drug discovery & development, and drug delivery. Many previous reviews have been mainly focused on the advantages of nanodiscs in membrane protein researches, but few have touched upon the importance and potential application of nanodiscs in pharmaceutical industries. This review will provide general description of the structural characteristics, advantages, classification, and applications of phospholipid nanodiscs, with particular focus on nanodisc-enabled membrane protein drug discovery & development as well as drug delivery.

Chemically-Induced Lipoprotein Breakdown for Improved Extracellular Vesicle Purification

Extracellular vesicles (EVs) are nanosized biomolecular packages involved in intercellular communication. EVs are released by all cells, making them broadly applicable as therapeutic, diagnostic, and mechanistic components in (patho)physiology. Sample purity is critical for correctly attributing observed effects to EVs and for maximizing therapeutic and diagnostic performance. Lipoprotein contaminants represent a major challenge for sample purity. Lipoproteins are approximately six orders of magnitude more abundant in the blood circulation and overlap in size, shape, and density with EVs. This study represents the first example of an EV purification method based on the chemically-induced breakdown of lipoproteins. Specifically, a styrene-maleic acid (SMA) copolymer is used to selectively breakdown lipoproteins, enabling subsequent size-based separation of the breakdown products from plasma EVs. The use of the polymer followed by tangential flow filtration or size-exclusion chromatography results in improved EV yield, preservation of EV morphology, increased EV markers, and reduced contaminant markers. SMA-based EV purification enables improved fluorescent labeling, reduces interactions with macrophages, and enhances accuracy, sensitivity, and specificity to detect EV biomarkers, indicating benefits for various downstream applications. In conclusion, SMA is a simple and effective method to improve the purity and yield of plasma-derived EVs, which favorably impacts downstream applications.

Solution NMR investigations of integral membrane proteins: Challenges and innovations

Compared to soluble protein counterparts, the understanding of membrane protein stability, solvent interactions, and function are not as well understood. Recent advancements in labeling, expression, and stabilization of membrane proteins have enabled solution nuclear magnetic resonance spectroscopy to investigate membrane protein conformational states, ligand binding, lipid interactions, stability, and folding. This review highlights these advancements and new understandings and provides examples of recent applications.

Detergent-Free Isolation of Membrane Proteins and Strategies to Study Them in a Near-Native Membrane Environment

Atomic-resolution structural studies of membrane-associated proteins and peptides in a membrane environment are important to fully understand their biological function and the roles played by them in the pathology of many diseases. However, the complexity of the cell membrane has severely limited the application of commonly used biophysical and biochemical techniques. Recent advancements in NMR spectroscopy and cryoEM approaches and the development of novel membrane mimetics have overcome some of the major challenges in this area. For example, the development of a variety of lipid-nanodiscs has enabled stable reconstitution and structural and functional studies of membrane proteins. In particular, the ability of synthetic amphipathic polymers to isolate membrane proteins directly from the cell membrane, along with the associated membrane components such as lipids, without the use of a detergent, has opened new avenues to study the structure and function of membrane proteins using a variety of biophysical and biological approaches. This review article is focused on covering the various polymers and approaches developed and their applications for the functional reconstitution and structural investigation of membrane proteins. The unique advantages and limitations of the use of synthetic polymers are also discussed.