ATP-Assisted Protocellular Membrane Formation with Ethanolamine-Based Amphiphiles

Exploring the Specific Role of Iron Center in the Catalytic Activity of Human Serum Transferrin: CTAB-Induced Conformational Changes and Sequestration by Mixed Micelles

Conformational changes play a seminal role in modulating the activity of proteins. This concept becomes all the more relevant in the context of metalloproteins, owing to the formation of specific conformation(s) induced by internal perturbations (like a change in pH, ligand binding, or receptor binding), which may carry out the binding and release of the metal ion/ions from the metal binding center of the protein. Herein, we investigated the conformational changes of an iron-binding protein, monoferric human serum transferrin (Fe-hTF), using several spectroscopic approaches. We could reversibly tune the cetyltrimethylammonium bromide (CTAB)-induced conformation of the protein, exploiting the concept of mixed micelles formed by three sequestrating agents: (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) hydrate (CHAPS) and two bile salts, namely, sodium cholate (NaC) and sodium deoxycholate (NaDC). The formation of mixed micelles between CTAB and these reagents (CHAPS/NaC/NaDC) results in the sequestration of CTAB molecules from the protein environment and aids the protein in reattaining its native-like structure. However, the guanidinium hydrochloride-induced denatured Fe-hTF did not acquire its native-like structure using these sequestrating agents, which substantiates the exclusive role of mixed micelles in the present study. Apart from this, we found that the conformation of transferrin (adopted in the presence of CTAB) displays pronounced esterase-like activity toward the para-nitrophenyl acetate (PNPA) substrate as compared to native transferrin. We also outlined the impact of the iron center and amino acids surrounding the iron center on the effective catalytic activity in the CTAB medium. We estimated ∼3 times higher specific catalytic efficiency for the iron-depleted Apo-hTF compared to the fully iron-saturated Fe2-hTF in the presence of CTAB.

Self-immolation Assisted Morphology Transformation of Prebiotic Lipidated-cationic Amino Acids: Electro-droplet Mediated C-C Coupling Reaction to Synthesize Macromolecules

Compartmentalization protected biomolecules from the fluctuating environments of early Earth. Although contemporary cells mostly use phospholipid-based bilayer membranes, the utility of non-bilayer compartments was not ruled out during the prebiotic and modern eras. In the present study, we demonstrated the prebiotic synthesis of lipidated cationic amino acid-based amphiphiles [lauryl ester of lysine (LysL); ornithine (OrnL); and 2,4-diamino butyric acid (DabL)] using model dry-down reaction. These amphiphiles self-assemble into micellar membranes. However, the OrnL and DabL-based micelles undergo pH-responsive transformation to lipid droplet-like morphologies, a modelcompartment in the prebiotic Earth. These cationic droplets encapsulated prebiotic molecules (isoprene) and assisted electron transfer reaction to synthesize isoprenoid derivatives at primitive Earth conditions. The self-assembly of prebiotic amphiphiles, their transformation to droplet compartments, and droplet-assisted C-C bond formation reaction might have helped the evolution to synthesize various biomolecules required for the origin of life.

Phosphate-Based Amphiphile and Lipidated Lysine Assemble into Superior Protocellular Membranes over Carboxylate and Sulfate-Based Systems: A Potential Missing Link between Prebiotic and the Modern Era?

Amphiphiles are among the most extensively studied building blocks that self-assemble into cell-like compartments. Most literature suggested that the building blocks/amphiphiles of early Earth (fatty acid-based membrane) were much simpler than today's phospholipids. To establish the bridge between the prebiotic fatty acid era and the modern phospholipid era, the investigation and characterization of alternate building blocks that form protocellular membranes are necessary. Herein, we report the potential prebiotic synthesis of alkyl phosphate, alkyl carboxylate, and alkyl sulfate amphiphiles (anionic) using dry-down reactions and demonstrate a more general role of cationic amino acid-based amphiphiles to recruit the anionic amphiphiles via ion-pair, hydrogen bonding, and hydrophobic interactions. The formation and self-assembly of the catanionic (mixed) amphiphilic system to vesicular morphology were characterized by turbidimetric, dynamic light scattering, transmission electron microscopy, fluorescence lifetime imaging microscopy, and glucose encapsulation experiments. Further experiments suggest that the phosphate-based vesicles were more stable than the alkyl sulfate and alkyl carboxylate-based systems. Moreover, the alkyl phosphate system can form vesicles at prebiotically relevant acidic pH (5.0), while alkyl carboxylate mainly forms cluster-type aggregates. An extended supramolecular polymer-type network formation via H-bonding and ion-pair interactions might order the membrane interface and stabilize the phosphate-based vesicles. The results suggest that phosphate-based amphiphiles might be a superior successor to fatty acids as early compartment building blocks. The work highlights the importance of previously unexplored building blocks that participate in protocellular membrane formation to encapsulate important precursors required for the functions of early life.