Impact of trifluoroethanol-induced structural changes on luciferase cleavage sites

A comparative study of structural and catalytic activity alterations in firefly luciferase induced by carbon quantum dots containing amine and carboxyl functional groups

Despite of growing interest in use of carbon-based nanomaterials as carriers of functional proteins, less attention has been paid to the effects of these nanomaterials on the structure and function of the proteins. In this study, with the aim of shedding light on the mechanisms of interaction between carbon-based nanomaterials and proteins, the interactions of carbon quantum dots (CQDs) containing amine (CQD-NH2) or carboxyl groups (CQD-COOH) with Photinus pyralis firefly luciferase enzyme were investigated by experimental and computational approaches. The structural changes and reduction in activity of the luciferase upon treatment with CQDs were experimentally proved. CQD-NH2 induced more reduction in enzyme activity (15 %) compared to CQD-COOH (7.4 %). The interactions CQD-NH2 with luciferase led to higher affinity of the enzyme for its substrate. It was found by molecular dynamic simulations that CQD-NH2 binds to multiple regions on the surface of luciferase. Secondary structure analysis showed that CQD-NH2 had more profound effects on the active site amino acids, the adjacent amino acids to the active site and the residues involved in ATP binding site. In addition, CQD-NH2 interactions with luciferase were suggested to be stronger than CQD-COOH based on the number of hydrogen bonds and the binding energies.

Trifluoroethanol and the behavior of a tardigrade desiccation-tolerance protein

The cosolvent 2,2,2-trifluoroethanol (TFE) is often used to mimic protein desiccation. We assessed the effects of TFE on cytosolic abundant heat soluble protein D (CAHS D) from tardigrades. CAHS D is a member of a unique protein class that is necessary and sufficient for tardigrades to survive desiccation. We find that the response of CAHS D to TFE depends on the concentration of both species. Dilute CAHS D remains soluble and, like most proteins exposed to TFE, gains α-helix. More concentrated solutions of CAHS D in TFE accumulate β-sheet, driving both gel formation and aggregation. At even higher TFE and CAHS D concentrations, samples phase separate without aggregation or increases in helix. Our observations show the importance of considering protein concentration when using TFE.

Deciphering the Mechanistic Basis for Perfluoroalkyl-Protein Interactions

Although rarely used in nature, fluorine has emerged as an important elemental ingredient in the design of proteins with altered folding, stability, oligomerization propensities, and bioactivity. Adding to the molecular modification toolbox, here we report the ability of privileged perfluorinated amphiphiles to noncovalently decorate proteins to alter their conformational plasticity and potentiate their dispersion into fluorous phases. Employing a complementary suite of biophysical, in-silico and in-vitro approaches, we establish structure-activity relationships defining these phenomena and investigate their impact on protein structural dynamics and intracellular trafficking. Notably, we show that the lead compound, perfluorononanoic acid, is 106 times more potent in inducing non-native protein secondary structure in select proteins than is the well-known helix inducer trifluoroethanol, and also significantly enhances the cellular uptake of complexed proteins. These findings could advance the rational design of fluorinated proteins, inform on potential modes of toxicity for perfluoroalkyl substances, and guide the development of fluorine-modified biologics with desirable functional properties for drug discovery and delivery applications.

Ordered structure-forming properties of the intrinsically disordered AB region of hRXRγ and its ability to promote liquid-liquid phase separation

The retinoid X receptor (RXR) is a member of the nuclear receptor (NR) superfamily that occupies the central position among other NRs by forming both homodimers and heterodimers with other representatives of the family. RXR shares similar structural domains with other members of NRs. The major differences in the subtypes and isoforms of RXR are in the AB region. To date, there have been no data concerning the molecular properties of the AB region of hRXRγ (AB_hRXG). Here, we describe the biochemical and biophysical properties of the recombinant AB_hRXG. The results indicate that AB_hRXG shows the structural and functional characteristics of the pre-molten globule-like (PMG-like) group of intrinsically disordered proteins (IDPs) and also has a significant propensity for folding. We also present the first experimental evidence showing that the AB region of NRs promotes the formation of liquid-liquid phase separation (LLPS).

About TFE: Old and New Findings

The fluorinated alcohol 2,2,2-Trifluoroethanol (TFE) has been implemented for many decades now in conformational studies of proteins and peptides. In peptides, which are often disordered in aqueous solutions, TFE acts as secondary structure stabilizer and primarily induces an α -helical conformation. The exact mechanism through which TFE plays its stabilizing roles is still debated and direct and indirect routes, relying either on straight interaction between TFE and molecules or indirect pathways based on perturbation of solvation sphere, have been proposed. Another still unanswered question is the capacity of TFE to favor in peptides a bioactive or a native-like conformation rather than simply stimulate the raise of secondary structure elements that reflect only the inherent propensity of a specific amino-acid sequence. In protein studies, TFE destroys unique protein tertiary structure and often leads to the formation of non-native secondary structure elements, but, interestingly, gives some hints about early folding intermediates. In this review, we will summarize proposed mechanisms of TFE actions. We will also describe several examples, in which TFE has been successfully used to reveal structural properties of different molecular systems, including antimicrobial and aggregation-prone peptides, as well as globular folded and intrinsically disordered proteins.

ΔFlucs: Brighter Photinus pyralis firefly luciferases identified by surveying consecutive single amino acid deletion mutations in a thermostable variant

The bright bioluminescence catalyzed by Photinus pyralis firefly luciferase (Fluc) enables a vast array of life science research such as bio imaging in live animals and sensitive in vitro diagnostics. The effectiveness of such applications is improved using engineered enzymes that to date have been constructed using amino acid substitutions. We describe ΔFlucs: consecutive single amino acid deletion mutants within six loop structures of the bright and thermostable ×11 Fluc. Deletion mutations are a promising avenue to explore new sequence and functional space and isolate novel mutant phenotypes. However, this method is often overlooked and to date there have been no surveys of the effects of consecutive single amino acid deletions in Fluc. We constructed a large semi-rational ΔFluc library and isolated significantly brighter enzymes after finding ×11 Fluc activity was largely tolerant to deletions. Targeting an "omega-loop" motif (T352-G360) significantly enhanced activity, altered kinetics, reduced Km for D-luciferin_, altered emission colors, and altered substrate specificity for redshifted analog DL-infraluciferin. Experimental and in silico analyses suggested remodeling of the Ω-loop impacts on active site hydrophobicity to increase light yields. This work demonstrates the further potential of deletion mutations, which can generate useful Fluc mutants and broaden the palette of the biomedical and biotechnological bioluminescence enzyme toolbox.

Bioanalytical approaches to assess the proteolytic stability of therapeutic fusion proteins

Therapeutic fusion proteins (TFPs) are designed to improve the therapeutic profile of an endogenous protein or protein fragment with a limited dose frequency providing the desired pharmacological activity in vivo. Fusion of a therapeutic protein to a half-life extension or targeting domain can improve the disposition of the molecule or introduce a novel mechanism of action. Prolonged exposure and altered biodistribution of an endogenous protein through fusion technology increases the potential for local protein unfolding during circulation increasing the chance for partial proteolysis of the therapeutic domain. Characterizing the proteolytic liabilities of a TFP can guide engineering efforts to inhibit or hinder partial proteolysis. This review focuses on considerations and techniques for evaluating the stability of a TFP both in vivo and in vitro.