Contributions of Components in Guanidine Hydrochloride to Hemoglobin Unfolding Investigated by Protein Film Electrochemistry

Refolding of Hemoglobin Under Macromolecular Confinement: Impersonating In Vivo Volume Exclusion

Biomacromolecules evolve and function inside the cell under crowded conditions. The effect of macromolecular crowding and confinement on nature and interactions of biomacromolecules cannot be ruled out. This study demonstrates the effect of volume exclusion due to macromolecular crowding on refolding rate of Gn-HCl induced unfolded hemoglobin. The in vivo like crowding milieu was created using dextran 70. Unfolding of Hb was followed by the absorbance at 280 nm and intrinsic fluorescence intensity along with a bathochromic shift that shows the destabilization of Hb in the presence of the denaturing agent. This was supported by a decrease in soret absorbance, increased hydrodynamic radii and loss in secondary structure, evidenced from dynamic light scattering and circular dichroism experiments respectively. Refolding process of Hb was followed by an increase in soret absorbance, decrease in intrinsic fluorescence intensity with a hypsochromic shift, decreased hydrodynamic radii and gain in secondary structural content. The results revealed that the effect of confinement and volume exclusion is insignificant on the process of Hb refolding.

Electrocatalysis by Heme Enzymes—Applications in Biosensing

Heme proteins take part in a number of fundamental biological processes, including oxygen transport and storage, electron transfer, catalysis and signal transduction. The redox chemistry of the heme iron and the biochemical diversity of heme proteins have led to the development of a plethora of biotechnological applications. This work focuses on biosensing devices based on heme proteins, in which they are electronically coupled to an electrode and their activity is determined through the measurement of catalytic currents in the presence of substrate, i.e., the target analyte of the biosensor. After an overview of the main concepts of amperometric biosensors, we address transduction schemes, protein immobilization strategies, and the performance of devices that explore reactions of heme biocatalysts, including peroxidase, cytochrome P450, catalase, nitrite reductase, cytochrome c oxidase, cytochrome c and derived microperoxidases, hemoglobin, and myoglobin. We further discuss how structural information about immobilized heme proteins can lead to rational design of biosensing devices, ensuring insights into their efficiency and long-term stability.

Investigating the Structural Change in Protein Aqueous Solution Using Temperature-Dependent Near-Infrared Spectroscopy and Continuous Wavelet Transform

The circulatory protein, human serum albumin (HSA), is widely used as a model protein for the study of protein structure. In this work, the structures of human serum albumin in aqueous solutions are studied using temperature-dependent near-infrared (NIR) spectroscopy with the aid of continuous wavelet transform (CWT). Near-infrared spectra of human serum albumin solutions with different concentrations were measured over a temperature range of 30-85 ℃. Then, continuous wavelet transform was performed on the spectra to enhance the resolution. As a result of the resolution enhancement, spectral bands around 4361, 4521, 4600 and 4260 cm^-1 were extracted from the overlapping low-resolution signals. The four bands can be assigned to the protein structures of α-helix, β-sheet, an intermediate state and side chains, respectively. The variations in intensity of the bands around 4361 and 4521 cm^-1 with temperature show that the increase of temperature leads to the loss of α-helical structure but the formation of β-sheet, and the denaturation temperature of human serum albumin is about 55 ℃. The variation of the band around 4600 cm^-1 indicates that the temperature-induced unfolding process of human serum albumin occurs through a stable intermediate state, and a significant change in the microenvironment of the side chains about 63 ℃ is observed from the variation of the band around 4260 cm^-1. On the other hand, the transformed spectra in the region of 8000-5600 cm^-1 provide an explicit evidence for the structural changes of water during the process of protein denaturation, and the unfolding process of HSA can be reflected by these changes.

Fourier transform infrared spectroscopy on external perturbations inducing secondary structure changes of hemoglobin

The secondary structure of proteins and their conformation are intimately related to their biological functions.

Viscosity-controlled printing of supramolecular-polymeric hydrogels via dual-enzyme catalysis

Hybrid hydrogels based on a guanidinium-containing oligopeptide are prepared via dual-enzyme-triggered reactions. An extended time window is available for in situ viscosity-controlled 3D printing.

Investigation of electrocatalytic pathway for hemoglobin toward nitric oxide by electrochemical approach based on protein controllable unfolding and in-situ reaction

An electrochemical approach based on protein controllable unfolding was developed and applied in combination with in-situ reaction in order to investigate the electrocatalytic pathway for hemoglobin (Hb) toward nitric oxide (NO). Hb was entrapped in a dimethyldidodecylammonium bromide (DDAB) film modified glassy carbon electrode (DDAB/Hb/GCE). Two typical denaturants of acid and urea were synergistically utilized to control the incorporated Hb to a most unfolded state without losing heme groups. Under optimal conditions, the unfolded DDAB/Hb/GCE exhibited accelerated direct electron transfer. The sensitivities for the detection of ascorbic acid (AA), NaNO(2) and NO were improved as 3, 10 and 12 times higher than those on the native DDAB/Hb/GCE, and the limits of detection (LODs) for AA, NaNO(2) and NO were down to 0.33, 0.83 and 0.063 μM, respectively. The unfolded DDAB/Hb/GCE was further applied for the investigation of Hb-NO interaction in NaNO(2) solution. With successive additions of AA, NO was generated in situ on DDAB/Hb/GCE. A new reduction peak of the intermediate HbFe(II)-HN(2)O(2) was successfully revealed near -0.65 V. The whole electrocatalytic mechanism was proposed and verified by density functional theory. The method can be a promising platform for facile study of the interaction between NO and heme proteins.

Insight into the effects of graphene oxide sheets on the conformation and activity of glucose oxidase: towards developing a nanomaterial-based protein conformation assay

Protein conformation associates with particular properties of proteins and relates to protein-mediated diseases. Detailed elucidation of secondary and tertiary formation, stability, and the structural and dynamic properties of proteins has been one of the main topics studied in chemistry and biology. In this work, the conformation changes in glucose oxidase (GOx) induced by the graphene oxide (GO) sheets were studied in detail by various spectroscopic techniques including ultraviolet-visible (UV-vis) absorption, fluorescence, and circular dichroism (CD) spectroscopy. The results indicated that GOx underwent substantial conformation changes after assembling on the surface of GO. The interaction of GOx with GO could induce the exposure of the FAD (flavin adenine dinucleotide) moiety to solvent and transfer tryptophan (Trp) residues to a more hydrophobic environment. The calculation from CD spectra showed that GO could induce the conversion of α-helix to β-sheet structures, even unfolding of the protein. These alterations in the conformation of GOx resulted in a significant decrease in the catalytic activity of the enzyme in glucose oxidation. The possible reasons for these conformation changes in GOx are also discussed. This work not only provides insight into the interaction between atomically flat graphitic structures and various biological systems but also creates a framework for analyzing the biosafety of nanomaterials in terms of the biological behavior of biomacromolecules. The results obtained here can direct the further applications of the nanomaterials.