Alpha casein micelles show not only molecular chaperone-like aggregation inhibition properties but also protein refolding activity from the denatured state

Weighted gene co-expression network analysis identifies modules and functionally enriched pathways in the lactation process

The exponential growth in knowledge has resulted in a better understanding of the lactation process in a wide variety of animals. However, the underlying genetic mechanisms are not yet clearly known. In order to identify the mechanisms involved in the lactation process, various mehods, including meta-analysis, weighted gene co-express network analysis (WGCNA), hub genes identification, gene ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment at before peak (BP), peak (P), and after peak (AP) stages of the lactation processes have been employed. A total of 104, 85, and 26 differentially expressed genes were identified based on PB vs. P, BP vs. AP, and P vs. AP comparisons, respectively. GO and KEGG pathway enrichment analysis revealed that DEGs were significantly enriched in the "ubiquitin-dependent ERAD" and the "chaperone cofactor-dependent protein refolding" in BP vs. P and P vs. P, respectively. WGCNA identified five significant functional modules related to the lactation process. Moreover, GJA1, AP2A2, and NPAS3 were defined as hub genes in the identified modules, highlighting the importance of their regulatory impacts on the lactation process. The findings of this study provide new insights into the complex regulatory networks of the lactation process at three distinct stages, while suggesting several candidate genes that may be useful for future animal breeding programs. Furthermore, this study supports the notion that in combination with a meta-analysis, the WGCNA represents an opportunity to achieve a higher resolution analysis that can better predict the most important functional genes that might provide a more robust bio-signature for phenotypic traits, thus providing more suitable biomarker candidates for future studies.

Combining different proteomic approaches to resolve complexity of the milk protein fraction of dromedary, Bactrian camels and hybrids, from different regions of Kazakhstan

Nutritional suitability of milk is not only related to gross composition, but is also strongly affected by the microheterogeniety of the protein fraction. Hence, to go further into the evaluation of the potential suitability of non-bovine milks in human/infant nutrition it is necessary to have a detailed characterization of their protein components. Combining proven proteomic approaches (SDS-PAGE, LC-MS/MS and LC-ESI-MS) and cDNA sequencing, we provide here in depth characterization of the milk protein fraction of dromedary and Bactrian camels, and their hybrids, from different regions of Kazakhstan. A total 391 functional groups of proteins were identified from 8 camel milk samples. A detailed characterization of 50 protein molecules, relating to genetic variants and isoforms arising from post-translational modifications and alternative splicing events, belonging to nine protein families (κ-, α_s1-, α_s2-, β-; and γ-CN, WAP, α-LAC, PGRP, CSA/LPO) was achieved by LC-ESI-MS. The presence of two unknown proteins UP1 (22,939 Da) and UP2 (23,046 Da) was also reported as well as the existence of a β-CN short isoform (946 Da lighter than the full-length β-CN), arising very likely in both genetic variants (A and B) from proteolysis by plasmin. In addition, we report, for the first time to our knowledge, the occurrence of a α_s2-CN phosphorylation isoform with 12P groups within two recognition motifs, suggesting thereby the existence of two kinase systems involved in the phosphorylation of caseins in the mammary gland. Finally, we demonstrate that genetic variants, which hitherto seemed to be species- specific (e.g. β-CN A for Bactrian and β-CN B for dromedary), are in fact present both in Camel dromedarius and C. bactrianus.

Solubilization of genistein by caseinate micellar system

This study investigates the aggregation behavior of caseinate and the solubilization of genistein in aqueous caseinate solution. The critical aggregation concentration (CAC) of caseinate was obtained from the fluorescence intensity of 8-anilino-1-naphthalenesulfonic acid (ANS), which was enhanced by ANS-protein interactions and the hydrophobicity of caseinate. The increasing solubility of genistein in caseinate was confirmed by HPLC measurements; above and below the CAC, the genistein/caseinate molar ratio is 1:1 and 10:1, respectively. The latter ratio indicates that more caseinate molecules surround genistein below the CAC. However, the solubility of genistein in caseinate is unaffected by calcium ions. Atomic force microscopy (AFM) shows that casein sub-micelles are similarly structured in the presence and absence of genistein. In AFM phase images, the caseinate sub-micelle is brightened in the presence of genistein, implying that the particle becomes more rigid, probably because genistein attaches to the surface or to the narrow part of the sub-micelle. The diameter of sub-micelle aggregates is two times that of caseinate alone (24 nm versus 12 nm). These results were confirmed by cryo-TEM observations.

α-Casein inhibition mechanism in concanavalin A aggregation process

The inhibition of the aggregation in protein solutions is currently a subject of great interest in many research fields, from the study of protein-misfolding related diseases to pharmaceutics, biotechnology, and food science. α(s1)-Casein, one of the four types of caseins, which are the largest protein component of bovine milk, has been found to hinder the aggregation process of several proteins, including the amyloid β-peptide, involved in Alzheimer's disease. To shed light into the mechanisms by which casein exerts this chaperon-like protective action, we studied its effect on the different steps of the aggregation process of concanavalin A, by means of both static and dynamic light scattering, thioflavin T and ANS fluorescence, circular dichroism, and atomic force microscopy. Our results show that casein has a poor effect on the first step of the process leading to the formation of amyloid-like structures. On the contrary, it has a marked effect on the second step of the process, ascribable to clusters condensation and compaction, up to the formation of very large aggregates. Such an effect requires a molar ratio of casein larger than that necessary to inhibit the fibrillogenesis of the amyloid β-peptide, thus, suggesting a different mechanism of interaction of casein, depending on both conformational properties and relative size of the aggregating molecules.

Chaperon-like Activation of Serum-Inducible Tryptophanyl-tRNA Synthetase Phosphorylation through Refolding as a Tool for Analysis of Clinical Samples

Tryptophanyl-tRNA synthetase (TrpRS) expression alters in colorectal (CRC), pancreatic (PC), and cervical (CC) cancers. Here, phosphorylation of unfolded TrpRS and its fragments is stimulated by human cancer sera (CS; n = 13) and serum of rabbit tumor induced by Rous sarcoma virus, unaffected by donor sera (NS; 11/15) and abolished by alkaline phosphatase. At 20 years of follow-up, serum-inducible TrpRS phosphorylation found years before healthy donors (3/15) diagnosed with PC, CRC, or leukemia. I have examined a specificity of serum-inducible TrpRS phosphorylation and found, surprisingly, that serine phosphorylation of unfolded TrpRS is stimulated by anti-TrpRS rabbit antisera but is unaffected by rabbit nonimmune sera and antisera to other antigens. Anti-TrpRS immunoglobulin G (IgG) inhibits phosphorylation of full-length TrpRS and stimulates phosphorylation of its 20-kDa fragment. Phosphorylation of this fragment is stimulated also by CS but not NS. 2-Mercaptoethanol and cyclic AMP exerted synergistic inhibitory effect on TrpRS phosphorylation. Anti-TrpRS sera and casein act as chaperones increasing TrpRS phosphorylation through refolding. Histone-specific protein kinase activity in CS (n = 44) and anti-TrpRS sera was lower than that in NS (n = 11), rabbit nonimmune sera and antisera to other antigens. TrpRS inhibitors, tryptamine, and tryptophanol stimulate in vivo accumulation of enzymatically inactive, nonphosphorylated, aggregated and anti-TrpRS IgG refoldable TrpRS. Phosphorylation of postsurgical tissues (n = 18) reveals TrpRS in ovarian cancer (OVC) and CC but not in normal placenta and liver. In OVC, TrpRS phosphorylation increase correlates with elevated tryptophan-dependent ATP-inorganic pyrophosphate exchange. Although not inducing cancer, TrpRS triggers signaling concomitant with cancer.