The thermal unfolding of the ribosome-inactivating protein saporin-S6 characterized by infrared spectroscopy

Despite their structural similarities, the cytosolic isoforms of human Hsp90 show different behaviour in thermal unfolding due to their conformation: An FTIR study

Heat shock proteins 90 (Hsp90) are chaperones that promote the proper folding of other proteins under high temperature stress situations. Hsp90s are highly conserved and ubiquitous proteins, and in mammalian cells, they are localized in the cytoplasm, endoplasmic reticulum, and mitochondria. Cytoplasmic Hsp90 are named Hsp90α and Hsp90β and differ mainly in their expression pattern: Hsp90α is expressed under stress conditions, while Hsp90β is a constitutive protein. Structurally, both share the same characteristics by presenting three well-conserved domains, one of which, the N-terminal domain, has a binding site for ATP to which various drugs targeting this protein, including radicicol, can bind. The protein is mainly found in dimeric form and adopts different conformations depending on the presence of ligands, co-chaperones and client proteins. In this study, some aspects of structure and thermal unfolding of cytoplasmic human Hsp90 were analysed by infrared spectroscopy. The effect on Hsp90β of binding with a non-hydrolysable ATP analogue and radicicol was also examined. The results obtained showed that despite the high similarity in secondary structure the two isoforms exhibit substantial differences in their behaviour during thermal unfolding, as Hsp90α exhibits higher thermal stability, slower denaturation process and different event sequence during unfolding. Ligand binding strongly stabilizes Hsp90β and slightly modifies the secondary structure of the protein as well. Most likely, these structural and thermostability characteristics are closely related to the conformational cycling of the chaperone and its propensity to exist in monomer or dimer form.

Prediction of breakage in human hair caused by cyclical extension using infrared spectroscopy coupled with multivariate curve resolution

We propose a method of prediction for hair breakage induced by change of molecular structure. The changes inside hair by cyclical extension were investigated using infrared (IR) spectroscopy coupled with multivariate curve resolution (MCR) and two-dimensional correlation spectroscopy (2D-COS). In bleached hair, cyclical extension stresses at 5% strain levels were seen to increase the signal of CH₂ and that of component primarily derived from C=O at 55 cycles, SO₃H signal at 75 cycles, ultimately leading to fiber breakage. The CH₂ profile of bleached hair significantly increased at 55 cycles compared to before extension in almost agreement with component profile primarily derived from C=O. This agreement behavior was likely to surface translocation of the lipids such as wax esters and triacylglycerols inside hair caused by cyclical extension. Two-dimensional correlation spectra indicated that SO₃H was produced by way of a cystine oxide by cyclical extension. In contrast, only CH₂ signal gradually increased without breakage in untreated hair. Thus, the method proposed in this study monitoring three functional groups is expected to have potential application in prediction of hair breakage by cyclical extension such as everyday grooming actions.

Isolation, Characterization and Biological Action of Type-1 Ribosome-Inactivating Proteins from Tissues of Salsola soda L

Ribosome-inactivating proteins (RIPs) are known as RNA N-glycosylases. They depurinate the major rRNA, damaging ribosomes and inhibiting protein synthesis. Here, new single-chain (type-1) RIPs named sodins were isolated from the seeds (five proteins), edible leaves (one protein) and roots (one protein) of Salsola soda L. Sodins are able to release Endo's fragment when incubated with rabbit and yeast ribosomes and inhibit protein synthesis in cell-free systems (IC₅₀ = 4.83-79.31 pM). In addition, sodin 5, the major form isolated from seeds, as well as sodin eL and sodin R, isolated from edible leaves and roots, respectively, display polynucleotide:adenosine glycosylase activity and are cytotoxic towards the Hela and COLO 320 cell lines (IC₅₀ = 0.41-1200 nM), inducing apoptosis. The further characterization of sodin 5 reveals that this enzyme shows a secondary structure similar to other type-1 RIPs and a higher melting temperature (Tm = 76.03 ± 0.30 °C) and is non-glycosylated, as other sodins are. Finally, we proved that sodin 5 possesses antifungal activity against Penicillium digitatum.

Sapovaccarin-S1 and -S2, Two Type I RIP Isoforms from the Seeds of Saponaria vaccaria L

Type I ribosome-inactivating proteins (RIPs) are plant toxins that inhibit protein synthesis by exerting rRNA N-glycosylase activity (EC 3.2.2.22). Due to the lack of a cell-binding domain, type I RIPs are not target cell-specific. However once linked to antibodies, so called immunotoxins, they are promising candidates for targeted anti-cancer therapy. In this study, sapovaccarin-S1 and -S2, two newly identified type I RIP isoforms differing in only one amino acid, were isolated from the seeds of Saponaria vaccaria L. Sapovaccarin-S1 and -S2 were purified using ammonium sulfate precipitation and subsequent cation exchange chromatography. The determined molecular masses of 28,763 Da and 28,793 Da are in the mass range typical for type I RIPs and the identified amino acid sequences are homologous to known type I RIPs such as dianthin 30 and saporin-S6 (79% sequence identity each). Sapovaccarin-S1 and -S2 showed adenine-releasing activity and induced cell death in Huh-7 cells. In comparison to other type I RIPs, sapovaccarin-S1 and -S2 exhibited a higher thermostability as shown by nano-differential scanning calorimetry. These results suggest that sapovaccarin-S1 and -S2 would be optimal candidates for targeted anti-cancer therapy.

The binding of different model membranes with PKCε C2 domain is not dependent on membrane curvature but affects the sequence of events during unfolding

The C2 domain of novel protein kinases C (nPKC) binds to membranes in a Ca²⁺-independent way contributing to the activation of these enzymes. We have studied the C2 domain of one of these nPKCs, namely PKCε, and confirmed that it establishes a strong interaction with POPA, which is clearly visible through changes in chemical shifts detected through ³¹P-MAS-NMR and the protection that it exerts on the domain against thermal denaturation seen through DSC and FT-IR. In this study, using two-dimensional correlation analysis (2D-COS) applied to infrared spectra, we determined the sequence of events that occur during the thermal unfolding of the domain and highlighted some differences when phosphatidic acid or cardiolipin are present. Finally, by means of FRET and DLS experiments, we wanted to determine the effect of membrane curvature on the domain/membrane interaction by using lysophosphatidylcholine to introduce positive curvature as a control and we observed that the effect of these phospholipids on the protein binding is not exerted through the change of membrane curvature.

Studies on the Interaction of Alyteserin 1c Peptide and Its Cationic Analogue with Model Membranes Imitating Mammalian and Bacterial Membranes

Antimicrobial peptides (AMPs) are effector molecules of the innate immune system and have been isolated from multiple organisms. Their antimicrobial properties are due to the fact that they interact mainly with the anionic membrane of the microorganisms, permeabilizing it and releasing the cytoplasmic content. Alyteserin 1c (+2), an AMP isolated from Alytes obstetricans and its more cationic and hydrophilic analogue (+5) were synthesized using the solid phase method, in order to study the interaction with model membranes by calorimetric and spectroscopic assays. Differential scanning calorimetry (DSC) showed that both peptides had a strong effect when the membrane contained phosphatidylcholine (PC) alone or was mixed with phosphatidylglycerol (PG), increasing membrane fluidization. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the secondary structure of the peptide. Peptide +2 exhibited a transition from β-sheet/turns to β-sheet/α-helix structures after binding with model membranes, whereas peptide +5 had a transition from aggregation/unordered to β-sheet/α-helix structures after binding with membrane-contained PC. Interestingly, the latter showed a β-sheet structure predominantly in the presence of PG lipids. Additionally, molecular dynamics (MD) results showed that the carboxy-terminal of the peptide +5 has the ability to insert into the surface of the PC/PG membranes, resulting in the increase of the membrane fluidity.

A Spectroscopic Study on Secondary Structure and Thermal Unfolding of the Plant Toxin Gelonin Confirms Some Typical Structural Characteristics and Unravels the Sequence of Thermal Unfolding Events

Gelonin from the Indian plant Gelonium multiflorum belongs to the type I ribosome-inactivating proteins (RIPs). Like other members of RIPs, this toxin glycoprotein inhibits protein synthesis of eukaryotic cells; hence, it is largely used in the construction of immunotoxins composed of cell-targeted antibodies. Lysosomal degradation is one of the main issues in targeted tumor therapies, especially for type I RIP-based toxins, as they lack the translocation domains. The result is an attenuated cytosolic delivery and a decrease of the antitumor efficacy of these plant-derived toxins; therefore, strategies to permit their release from endosomal vesicles or modifications of the toxins to make them resistant to degradation are necessary to improve their efficacy. Using infrared spectroscopy, we thoroughly analyzed both the secondary structure and the thermal unfolding of gelonin. Moreover, by the combination of two-dimensional correlation spectroscopy and phase diagram method, it was possible to deduce the sequence of events during the unfolding, confirming the typical characteristic of the RIP members to denature in two steps, as a sequential loss of tertiary and secondary structure was detected at 58 °C and at 65 °C, respectively. Additionally, some discrepancies in the unfolding process between gelonin and saporin-S6, another type I RIP protein, were detected.

Interaction of γ-conglutin from Lupinus albus with model phospholipid membranes: Investigations on structure, thermal stability and oligomerization status

Interaction with model phospholipid membranes of lupin seed γ-conglutin, a glycaemia-lowering protein from Lupinus albus seeds, has been studied by means of Fourier-Transform infrared spectroscopy at p²H 7.0 and at p²H 4.5. The protein maintains the same secondary structure both at p²H 7.0 and at p²H 4.5, but at p²H 7.0 a higher ¹H/²H exchange was observed, indicating a greater solvent accessibility. The difference in T_m and T_D1/2 of the protein at the abovementioned p²H's has been calculated around 20 °C. Infrared measurements have been then performed in the presence of DMPG and DOPA at p²H 4.5. DMPG showed a little destabilizing effect while DOPA exerted a great stabilizing effect, increasing the T_m of γ-conglutin at p²H 4.5 of more than 20 °C. Since γ-conglutin at p²H 4.5 is in the monomeric form, the interaction with DOPA likely promotes the oligomerization even at p²H 4.5. Interaction between DMPG or DOPA and γ-conglutin has been confirmed by turbidity experiments with DMPC:DMPG or DOPC:DOPA SUVs. Turbidity data also showed high-affinity binding of γ-conglutin to anionic SUVs made up with DOPA. The molecular features outlined in this study are relevant to address the applicative exploitation and to delineate a deeper comprehension of the natural functional role of γ-conglutin.

The conformation of bovine serum albumin adsorbed to the surface of single all-dielectric nanoparticles following light-induced heating

Interaction between nanoparticles and biomolecules leads to the formation of biocompatible or bioadverse complexes. Despite the rapid development of nanotechnologies for biology and medicine, relatively little is known about the structure of such complexes. Here, we report on the changes in conformation of a blood protein (bovine serum albumin) adsorbed on the surface of single all-dielectric nanoparticles (silicon and germanium) following light-induced heating to 640 K. This protein is considerably more resistant to heat when adsorbed on the nanoparticle than when in solution or in the solid state. Intriguingly, with germanium nanoparticles this heat resistance is more pronounced than with silicon. These observations will facilitate biocompatible usage of all-dielectric nanoparticles.

Advancements of two dimensional correlation spectroscopy in protein researches

The developments of two-dimensional correlation spectroscopy (2DCOS) applications in protein studies are discussed, especially for the past two decades. The powerful utilities of 2DCOS combined with various analytical techniques in protein studies are summarized. The emphasis is on the vibration spectroscopic techniques including IR, NIR, Raman and optical activity (ROA), as well as vibration circular dichroism (VCD) and fluorescence spectroscopy. In addition, some new developments, such as hetero-spectral 2DCOS, moving-window correlation, and model based correlation, are also reviewed for their utility in the investigation of the secondary structure, denaturation, folding and unfolding changes of protein. Finally, the new possibility and challenges of 2DCOS in protein research are highlighted as well.

Two-dimensional correlation spectroscopy in protein science, a summary for past 20years

Two-dimensional correlation spectroscopy (2DCOS) has been widely used to Infrared, Raman, Near IR, Optical Activity (ROA), Vibrational Circular Dichroism (VCD) and Fluorescence spectroscopy. In addition, several new developments, such as 2D hetero-correlation analysis, moving-window two-dimensional (MW2D) correlation, model based correlation (βν and kν correlation analyses) have also well incorporated into protein research. They have been used to investigate secondary structure, denaturation, folding and unfolding changes of protein, and have contributed greatly to the field of protein science. This review provides an overview of the applications of 2DCOS in the field of protein science for the past 20 year, especially to memory our old friend, Dr. Boguslawa Czarnik-Matusewicz, for her great contribution in this research field. The powerful utility of 2DCOS combined with various analytical techniques in protein studies is summarized. The noteworthy developments and perspective of 2DCOS in this field are highlighted finally.

Ribosome-Inactivating Proteins from Plants: A Historical Overview

This review provides a historical overview of the research on plant ribosome-inactivating proteins (RIPs), starting from the first studies at the end of eighteenth century involving the purification of abrin and ricin, as well as the immunological experiments of Paul Erlich. Interest in these plant toxins was revived in 1970 by the observation of their anticancer activity, which has given rise to a large amount of research contributing to the development of various scientific fields. Biochemistry analyses succeeded in identifying the enzymatic activity of RIPs and allowed for a better understanding of the ribosomal machinery. Studies on RIP/cell interactions were able to detail the endocytosis and intracellular routing of ricin, thus increasing our knowledge of how cells handle exogenous proteins. The identification of new RIPs and the finding that most RIPs are single-chain polypeptides, together with their genetic sequencing, has aided in the development of new phylogenetic theories. Overall, the biological properties of these proteins, including their abortifacient, anticancer, antiviral and neurotoxic activities, suggest that RIPs could be utilized in agriculture and in many biomedical fields, including clinical drug development.

Property and structure changes of myofibril protein in pork treated by high pressure combined with heat

The effects of myofibril protein in pork treated by high hydrostatic pressure combined with heat were investigated. The solubility of myofibril protein significantly increased up to 400 MPa but since then began to decrease up to 600 MPa. The best solubility was shown under all pressure at 35 ℃ and the lowest solubility was observed at 55 ℃. The carbonyl group value, disulfide bond and surface hydrophobicity exhibited pressure-dependent increase in the same manner. Particle size decreased up to 400 MPa and then increased up to 600 MPa, but the turbidity always reduced. The increase of intrinsic fluorescence intensity with red shift and decrease of absorbance around 278 nm with blue shift indicated that protein unfolding and exposure of hydrophobic amino acid occurred with increase of pressure. The second derivative infrared spectra and curve fittings suggested that high pressure induced reduction of β-sheet structures, enhancement of α-helix and random coil and β-turns segments, which was opposite to the effects of temperature. Emission scanning electron microscope assay further demonstrated protein unfolding and aggregation process induced by different pressure and temperature. The data suggested that cooperative effect of moderate pressure and temperature could improve physical-chemical and processing properties of meat.