Origin of the anomalous circular dichroism spectra of many apomyoglobin mutants

Deciphering the mechanism of hafnium oxide nanoparticles perturbation in the bio-physiological microenvironment of catalase

Nanoparticles (NPs) are extensively being used in state-of-the-art nano-based therapies, modern electronics, and consumer products, so can be released into the environment with enhancement interaction with humans. Hence, the exposures to these multifunctional NPs lead to changes in protein structure and functionality, raising serious health issues. This study thoroughly investigated the interaction and adsorption of catalase (CAT) with HfO2-NPs by circular dichroism (CD), Fourier transform infrared (FTIR), absorption, and fluorescence spectroscopic techniques. The results indicate that HfO2 NPs cause fluorescence quenching in CAT by a static quenching mechanism. The negative values of Vant Hoff thermodynamic expressions (ΔH o , ΔS o , and ΔG o ) corroborate the spontaneity and exothermic nature of static quenching driven by van der Waals forces and hydrogen bonding. Also, FTIR, UV-CD, and UV–visible spectroscopy techniques confirmed that HfO2 NPs binding could induce microenvironment perturbations leading to secondary and tertiary conformation changes in CAT. Furthermore, synchronous fluorescence spectroscopy confirmed the significant changes in the microenvironment around tryptophan (Trp) residue caused by HfO2 NPs. The time depending denaturing of CAT biochemistry through HfO2-NPs was investigated by assaying catalase activity elucidates the potential toxic action of HfO2-NPs at the macromolecular level. Briefly, this provides an empathetic knowledge of the nanotoxicity and likely health effects of HfO2 NPs exposure.

Effect of high pressure on structural modifications and enzymatic activity of a purified X-prolyl dipeptidyl aminopeptidase from Streptococcus thermophilus

PepX aminopeptidase from Streptococcus thermophilus ACA DC 0022, used in Greek Feta cheese manufacturing, was purified. PepX comprises two subunits of equal molecular mass estimated, using SDS-PAGE and native-PAGE electrophoresis, to be 86 kDa. The effects of high pressure processing (100-450 MPa, combined with 20-40 °C) on purified PepX activity and structure were studied. Activation of the enzyme was observed after processing at 100-200 MPa and 20-30 °C. More intense processing conditions led to enzyme inactivation. PepX HP-induced conformational changes were also investigated through application of Circular Dichroism spectroscopy (CD). Pressures up to 200 MPa resulted in a structurally molten globule-like state where PepX maintained its secondary structure but the tertiary structure was substantially affected and enzyme activity increased. Both secondary and tertiary structures were affected severely by higher pressures (450 MPa), which reduced enzyme activity.

The structure and regulation of human muscle α-actinin

The spectrin superfamily of proteins plays key roles in assembling the actin cytoskeleton in various cell types, crosslinks actin filaments, and acts as scaffolds for the assembly of large protein complexes involved in structural integrity and mechanosensation, as well as cell signaling. α-actinins in particular are the major actin crosslinkers in muscle Z-disks, focal adhesions, and actin stress fibers. We report a complete high-resolution structure of the 200 kDa α-actinin-2 dimer from striated muscle and explore its functional implications on the biochemical and cellular level. The structure provides insight into the phosphoinositide-based mechanism controlling its interaction with sarcomeric proteins such as titin, lays a foundation for studying the impact of pathogenic mutations at molecular resolution, and is likely to be broadly relevant for the regulation of spectrin-like proteins.

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Structure of human α-actinin-2 in an autoinhibited closed conformation

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Facilitation of PIP2-induced allosteric modulation for opening and titin binding

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Essentiality of structural flexibility for crosslinking antiparallel F-actin

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Relevance for the intramolecular pseudoligand regulation mechanism of the spectrin family

Purification of a crystallin domain of Yersinia crystallin from inclusion bodies and its comparison to native protein from the soluble fraction

It has been established that many heterologously produced proteins in E. coli accumulate as insoluble inclusion bodies. Methods for protein recovery from inclusion bodies involve solubilization using chemical denaturants such as urea and guanidine hydrochloride, followed by removal of denaturant from the solution to allow the protein to refold. In this work, we applied on-column refolding and purification to the second crystallin domain D2 of Yersinia crystallin isolated from inclusion bodies. We also purified the protein from the soluble fraction (without using any denaturant) to compare the biophysical properties and conformation, although the yield was poor. On-column refolding method allows rapid removal of denaturant and refolding at high protein concentration, which is a limitation in traditionally used methods of dialysis or dilution. We were also able to develop methods to remove the co-eluting nucleic acids during chromatography from the protein preparation. Using this protocol, we were able to rapidly refold and purify the crystallin domain using a two-step process with high yield. We used biophysical techniques to compare the conformation and calcium-binding properties of the protein isolated from the soluble fraction and inclusion bodies.

On the difference in stability between horse and sperm whale myoglobins

The work in the literature on apomyoglobin is almost equally divided between horse and sperm whale myoglobins. The two proteins share high homology, show similar folding behavior, and it is often assumed that all folding phenomena found with one protein will also be found with the other. We report data at equilibrium showing that horse myoglobin was 2.1 kcal/mol less stable than sperm whale myoglobin at pH 5.0, and aggregated at high concentrations as measured by gel filtration and analytical ultracentrifugation experiments. The higher stability of sperm whale myoglobin was identified for both apo and holo forms, and was independent of pH from 5 to 8 and of the presence of sodium chloride. We also show that the substitution of sperm whale myoglobin residues Ala15 and Ala74 to Gly, the residues found at positions 15 and 74 in horse myoglobin, decreased the stability by 1.0 kcal/mol, indicating that helix propensity is an important component of the explanation for the difference in stability between the two proteins.