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Ferritin is a ubiquitous intracellular iron storage protein that plays a crucial role in iron homeostasis. Animal tissue ferritins consist of multiple isoforms (or isoferritins) with different proportions of H and L subunits that contribute to their structural and compositional heterogeneity, and thus physiological functions. Using size exclusion and anion exchange chromatography, capillary isoelectric focusing (cIEF), and SDS-capillary gel electrophoresis (SDS-CGE), we reveal for the first time a significant variation in ferritin subunit composition and isoelectric points, in both recombinant and native ferritins extracted from animal organs. Our results indicate that subunits composition is the main determinant of the mean pI of recombinant ferritin heteropolymers, and that ferritin microheterogeneity is a common property of both natural and recombinant proteins and appears to be an intrinsic feature of the cellular machinery during ferritin expression, regulation, post-translational modifications, and post-subunits assembly. The functional significance and physiological implications of ferritin heterogeneity in terms of iron metabolism, response to oxidative stress, tissue-specific functions, and pathological processes are discussed.

The pressing need for protein supply growth gives rise to alternative protein sources, such as insect proteins. Commercial cricket and mealworm powders were examined for their protein quality, surface charge and functional attributes. Both insect powders had similar proximate compositions with protein and ash contents of ~ 66% db (dry weight basis) and 5% db, respectively, however cricket powder contained more lipid (16.1%, db) than mealworm powder (13.7%, db). Mealworm protein had an amino acid score of 0.71 and was first limiting in lysine, whereas cricket protein was first limiting in tryptophan with an amino acid score of 0.85. In vitro protein digestibility values of 75.7% and 76.2%, and in vitro protein digestibility corrected amino acid scores of 0.54 and 0.65, were obtained for mealworm and cricket powders, respectively. Zeta potential measurements gave isoelectric points near pH 3.9 for both insect powders. Mealworm and cricket powders had water hydration capacities of 1.62 g/g and 1.76 g/g, respectively, and oil holding capacities of 1.58 g/g and 1.42 g/g, respectively. Both insect proteins had low solubility (22–30%) at all pHs (3.0, 5.0, and 7.0) measured. Cricket powder had a foaming capacity of 82% and foam stability of 86%, whereas mealworm powder was non-foaming. Values for commercial pea and faba bean protein concentrates were reported for comparative purposes. The insect proteins had similar protein quality as the pulse proteins and had higher solubility at pH 5.0 but were much less soluble at pH 7.0.

The association of the S-protein of the SARS-CoV-2 beta coronavirus to ACE2 receptors of the human epithelial cells determines its contagiousness and pathogenicity. We computed the pH-dependent electric potential on the surface of the interacting globular proteins and pH-dependent Gibbs free energy at the association of the wild-type strain and the omicron variant. The calculated isoelectric points of the ACE2 receptor (pI 5.4) and the S-protein in trimeric form (pI 7.3, wild type), (pI 7.8, omicron variant), experimentally verified by isoelectric focusing, show that at pH 6–7, the S1–ACE2 association is conditioned by electrostatic attraction of the oppositely charged receptor and viral protein. The comparison of the local electrostatic potentials of the omicron variant and the wild-type strain shows that the point mutations alter the electrostatic potential in a relatively small area on the surface of the receptor-binding domain (RBD) of the S1 subunit. The appearance of seven charge-changing point mutations in RBD (equivalent to three additional positive charges) leads to a stronger S1–ACE2 association at pH 5.5 (typical for the respiratory tract) and a weaker one at pH 7.4 (characteristic of the blood plasma); this reveals the reason for the higher contagiousness but lower pathogenicity of the omicron variant in comparison to the wild-type strain.

Cytokinins play an important role in plants and are targets of wheat breeding, particularly in terms of flowering and yield. The objective of this study was to determine relative synonymous codon usage (RSCU), molecular weight (g/mol), theoretical isoelectric point, instability index, aliphatic index, and hydrophobicity for the wheat cytokinin sequences from two different databases. The methods employed involved different formulas for calculations. The relative synonymous codon usage values were calculated as the ratio of the observed frequency to the expected frequency for the particular codon. The theoretical isoelectric point was calculated based on dissociation constant for groups of carboxylic acid and amino acids groups. The results showed that values of the relative synonymous codon usage divided amino acids of wheat into two groups. In the first group, values were above 1.6 (significant overrepresentation), such as those for phenylalanine (TTC), and Leucine (TTA). In the second group, values were below 0.6 (underrepresentation) such as those for leucine (CTA) and valine (GTT). In addition, the theoretical isoelectric point (pI) ranged from 4.81 to 6.6, and the instability index values were 34.3 and 38.16. A high degree of instability was observed at 1D and 5D of wheat genomes with values of 54.16 and 50.36, respectively. Principal component analysis (PCA) of the RSCU revealed that the main variation was attributed to PC1, accounting for a total variation of about 72.11%. The amino acids contributing to this variation included isoleucine, leucine, lysine, aspartic acid, and serine. PCA of the theoretical isoelectric point results found that the main variation was attributed to PC1, with a total variation of about 58.88%, and these chromosomes included 5D, 4D, 1A, 4B, and 3D of wheat genomes. Understanding the importance of RSCU in plant breeding helps breeders understand the mechanisms and functional aspects of wheat genomes, thereby enabling the development of wheat genomes for environmental adaptations. These results will provide a reference for nutrition and industrial applications, as well as supporting breeding programs.

Despite the apparent importance of matrix proteins in calcium oxalate kidney stone formation, the complexity of the protein mixture continues to elude explanation. Based on a series of experiments, we have proposed a model where protein aggregates formed from a mixture containing both strongly charged polyanions and strongly charged polycations could initiate calcium oxalate crystal formation and crystal aggregation to create a stone. These protein aggregates also preferentially adsorb many weakly charged proteins from the urine to create a complex protein mixture that mimics the protein distributions observed in patient samples. To verify essential details of this model and identify an explanation for phase selectivity observed in weakly charged proteins, we have examined primary structures of major proteins preferring either the matrix phase or the urine phase for their contents of aspartate, glutamate, lysine and arginine; amino acids that would represent fixed charges at normal urine pH of 6–7. We verified enrichment in stone matrix of proteins with a large number of charged residues exhibiting extreme isoelectric points, both low (pI<5) and high (pI>9). We found that the many proteins with intermediate isoelectric points exhibiting preference for stone matrix contained a smaller number of charge residues, though still more total charges than the intermediate isoelectric point proteins preferring the urine phase. While other sources of charge have yet to be considered, protein preference for stone matrix appears to correlate with high total charge content.

Sodium dodecyl sulphate (SDS), an anionic surfactant that mimics some characteristics of biological membrane has also been found to induce aggregation in proteins. The present study was carried out on 25 diverse proteins using circular dichroism, fluorescence spectroscopy, dye binding assay and electron microscopy. It was found that an appropriate molar ratio of protein to SDS readily induced amyloid formation in all proteins at a pH below two units of their respective isoelectric points (pI) while no aggregation was observed at a pH above two units of pI. We also observed that electrostatic interactions play a leading role in the induction of amyloid. This study can be used to design or hypothesize a molecule or drug, which may counter act the factor responsible for amyloid formation.

The aqueous solubility of L-tryptophan was measured with a wide range of pH (1.00–12.50) and different monovalent counterions (Na + , K + , Cl − and NO 3 - ) from 283.15 to 323.15 K by using a static equilibrium method. The results showed that the solubility of L-tryptophan increased with increasing temperature and the solubility–pH profile was a “U” shape with the lowest value at the isoelectric point. Additionally, the distribution of the ionic forms of L-tryptophan as a function of pH was obtained using the knowledge of the acid–base equilibria of amino acids, and it was found that the isoelectric points increased with temperature. Moreover, different counterions were introduced by using different acids or bases during pH adjustment and their effect on the solubility of L-tryptophan was investigated, which showed that more L-tryptophan could be dissolved in the presence of K + (or NO 3 - ) than Na + (or Cl − ). Besides, the modified Apelblat model and the NRTL model were successfully used to correlate the aqueous solubility data with all the average relative deviation less than 2.1%.

We report on the systematic investigation of the role of surface nanoscale roughness and morphology on the charging behaviour of nanostructured titania (TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces have been characterized by direct measurement of the electrostatic double layer interactions between titania surfaces and the micrometer-sized spherical silica probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a colloidal probe provides well-defined interaction geometry and allows effectively probing the overall effect of nanoscale morphology. By using supersonic cluster beam deposition to fabricate nanostructured titania films, we achieved a quantitative control over the surface morphological parameters. We performed a systematical exploration of the electrical double layer properties in different interaction regimes characterized by different ratios of characteristic nanometric lengths of the system: the surface rms roughness Rq, the correlation length ξ and the Debye length λD. We observed a remarkable reduction by several pH units of IEP on rough nanostructured surfaces, with respect to flat crystalline rutile TiO2. In order to explain the observed behavior of IEP, we consider the roughness-induced self-overlap of the electrical double layers as a potential source of deviation from the trend expected for flat surfaces.

Background Haloarchaea, a major group of archaea, are able to metabolize sugars and to live in oxygenated salty environments. Their physiology and lifestyle strongly contrast with that of their archaeal ancestors. Amino acid optimizations, which lowered the isoelectric point of haloarchaeal proteins, and abundant lateral gene transfers from bacteria have been invoked to explain this deep evolutionary transition. We use network analyses to show that the evolution of novel genes exclusive to Haloarchaea also contributed to the evolution of this group. Results We report the creation of 320 novel composite genes, both early in the evolution of Haloarchaea during haloarchaeal genesis and later in diverged haloarchaeal groups. One hundred and twenty-six of these novel composite genes derived from genetic material from bacterial genomes. These latter genes, largely involved in metabolic functions but also in oxygenic lifestyle, constitute a different gene pool from the laterally acquired bacterial genes formerly identified. These novel composite genes were likely advantageous for their hosts, since they show significant residence times in haloarchaeal genomes—consistent with a long phylogenetic history involving vertical descent and lateral gene transfer—and encode proteins with optimized isoelectric points. Conclusions Overall, our work encourages a systematic search for composite genes across all archaeal major groups, in order to better understand the origins of novel prokaryotic genes, and in order to test to what extent archaea might have adjusted their lifestyles by incorporating and recycling laterally acquired bacterial genetic fragments into new archaeal genes.

Membrane proteins play key roles in cellular functions like transport of molecules, perception of environmental cues, and signal transduction into the intracellular compartment. However, the profiling of membrane proteins is still a daunting task because of the hydrophobicity, restricting our knowledge of membrane proteins. Thus, we attempted to develop a novel detergent-based approach to uncover membrane proteins using cyanobacteria. We investigated the effect of five different detergents on the profiling of the cyanobacterial membrane proteome. The application of either amidosulfobetaine-14 (ASB14) or N-lauroylsarcosine (NL) doubled the number of the identified integral membrane proteins compared with the control. Extraction with ASB14 increased the number of transmembrane helices over four times. The quantitative index (mol%) of membrane proteins also increased from 13 to 22% when ASB14, NL, and benzyldimethyl-n-hexadecylammonium chloride (BAC) were used. ASB14 treatment was particularly useful for identifying membrane proteins with higher molecular weights (Mr), and the addition of BAC to the cyanobacterial membrane could identify the membrane proteins with acidic isoelectric points (pI). To validate the efficiency of the detergent-based proteomics, the functional membrane protein complexes involved in energy metabolism were selected as an example and shown to be successful with the combined data of ASB14, NL, and zwittergent 3-10 (ZW3-10). Taken together, we suggest that the use of a specific detergent and the subsequent combination of proteome data is critical for detailed profiling of cyanobacterial functional membrane proteins.