Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein

Structure and effective charge characterization of proteins by a mobility capillary electrophoresis based method

Measuring the conformations and effective charges of proteins in solution is critical for investigating protein bioactivity, but their rapid analysis remains a challenging problem. Here we report a mobility capillary electrophoresis (MCE) based method for the rapid analysis of protein stereo-structures and effective charges in different solution environments. With the capability of mixture separation, MCE measures the hydrodynamic radius of a protein through Taylor dispersion analysis and its effective charge through ion mobility analysis. The experimental results acquired from MCE are then utilized to restrain molecular dynamics simulations, so that the most probable conformation of that protein can be obtained. As proof-of-concept demonstrations, the charge states and structures of five proteins were analyzed under close to native environments. The conformation transitions and charge state variations of bovine serum albumin and lysozyme under different pH conditions were also investigated. This method is promising for high-throughput protein analysis, which could potentially be coupled with mass spectrometry for investigating protein stereo-structures and functions in top-down proteomics.

Characterization of protein extracts from different types of human teeth and insight in biomineralization

The present study describes an efficient method for isolation and purification of protein extracts from four types of human teeth i.e. molar, premolar, canine, and incisor. Detailed structural characterization of these protein extracts was done by Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) which showed that a major fraction of the proteins present are unstructured in nature including primarily random coils in addition to the other structures like extended beta (β) structure, poly-l-proline-type II (PPII) helix, turns, with only a small fraction constituting of ordered structures like alpha (α) helix and β sheets. These resultant labile structures give the proteins the necessary flexibility that they require to interact with a variety of substrates including different ions like calcium and phosphates and for other protein-protein interactions. We also did initial studies on the mineralization of calcium phosphate with the protein extracts. Nanoparticle tracking analysis (NTA) show an increase in the size of calcium phosphate accumulation in the presence of protein extracts. We propose that protein extracts elevate the crystallization process of calcium phosphate. Our current biophysical study provides novel insights into the structural characterization of proteins from human teeth and their implications in understanding the tooth biomineralization. As per our knowledge, this is the first report which focuses on the whole protein extraction from different types of human teeth as these extracts imitate the in vivo tooth mineralization.

Low intensity electric field inactivation of Gram-positive and Gram-negative bacteria via metal-free polymeric composite

The adhesion of pathogenic bacteria in medical implants and surfaces is a health-related problem that requires strong inhibition against bacterial growth and attachment. In this work, we have explored the enhancement in the antibacterial activity of metal free-based composites under external electric field. It affects the oxidation degree of polypyrrole-based electrodes and consequently the antibacterial activity of the material. A conductive layer of carbon nanotubes (graphite) was deposited on porous substrate of polyurethane (sandpaper) and covered by polypyrrole, providing highly conductive electrodes characterized by intrinsic antibacterial activity and reinforced by electro-enhanced effect due to the external electric field. The bacterial inhibition of composites was monitored from counting of viable cells at different voltage/time of treatment and determination of biofilm inhibition on electrodes and reactors. The external voltage on electrodes reduces the threshold time for complete bacterial inactivation of PPy-based composites to values in order of 30 min for Staphylococcus aureus and 60 min for Escherichia coli.

Cloning, purification and characterization of nigrelysin, a novel actinoporin from the sea anemone Anthopleura nigrescens

Actinoporins constitute a unique class of pore-forming toxins found in sea anemones that being secreted as soluble monomers are able to bind and permeabilize membranes leading to cell death. The interest in these proteins has risen due to their high cytotoxicity that can be properly used to design immunotoxins against tumor cells and antigen-releasing systems to cell cytosol. In this work we describe a novel actinoporin produced by Anthopleura nigrescens, an anemone found in the Central American Pacific Ocean. Here we report the amino acid sequence of an actinoporin as deduced from cDNA obtained from total body RNA. The synthetic DNA sequence encoding for one cytolysin variant was expressed in BL21 Star (DE3) Escherichia coli and the protein purified by chromatography on CM Sephadex C-25 with more than 97% homogeneity as verified by MS-MS and HPLC analyses. This actinoporin comprises 179 amino acid residues, consistent with its observed isotope-averaged molecular mass of 19 661 Da. The toxin lacks Cys and readily permeabilizes erythrocytes, as well as L1210 cells. CD spectroscopy revealed that its secondary structure is dominated by beta structure (58.5%) with 5.5% of α-helix, and 35% of random structure. Moreover, binding experiments to lipidic monolayers and to liposomes, as well as permeabilization studies in vesicles, revealed that the affinity of this toxin for sphingomyelin-containing membranes is quite similar to sticholysin II (StII). Comparison by spectroscopic techniques and modeling the three-dimensional structure of nigrelysin (Ng) showed a high homology with StII but several differences were also detectable. Taken together, these results reinforce the notion that Ng is a novel member of the actinoporin pore-forming toxin (PFT) family with a HA as high as that of StII, the most potent actinoporin so far described, but with peculiar structural characteristics contributing to expand the understanding of the structure-function relationship in this protein family.

Arsenite Targets the RING Finger Domain of Rbx1 E3 Ubiquitin Ligase to Inhibit Proteasome-Mediated Degradation of Nrf2

Activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant response signaling pathway is a major mechanism for the cellular defense against oxidative stress. Arsenite, a widespread contaminant in drinking water, is known to induce oxidative stress and activate the Nrf2-dependent signaling pathway through the stabilization of the Nrf2 protein by inhibiting its ubiquitination via the Cul3-Rbx1-Keap1 (cullin 3, RING-box 1, and Kelch-like ECH-associated protein 1) E3 ubiquitin ligase, and its degradation by the 26S proteasome, though the underlying mechanism, remains elusive. In the present study, we demonstrated that arsenite could bind to the RING finger domain of Rbx1 in vitro and in cells, which led to the suppression of Cul3-Rbx1 E3 ubiquitin ligase activity, thereby impairing the Nrf2 ubiquitination and activating the Nrf2-induced antioxidant signaling pathway. Our finding provided novel insight into arsenic toxicity by uncovering a distinct mechanism accounting for arsenite-induced Nrf2 activation.

Optical backbone-sidechain charge transfer transitions in proteins sensitive to secondary structure and modifications

We report the UV-vis absorption originating from protein backbone-sidechain charge transfer transitions in charged amino acids with anionic and cationic sidechains.

Protein charge transfer absorption spectra: an intrinsic probe to monitor structural and oligomeric transitions in proteins

The utility of ProCharTS as an intrinsic spectral probe to track protein aggregation and monitor conformational changes is reported.