Ibuprofen Favors Binding of Amyloid-β Peptide to Its Depot, Serum Albumin

The deposition of amyloid-β peptide (Aβ) in the brain is a critical event in the progression of Alzheimer’s disease (AD). This Aβ deposition could be prevented by directed enhancement of Aβ binding to its natural depot, human serum albumin (HSA). Previously, we revealed that specific endogenous ligands of HSA improve its affinity to monomeric Aβ. We show here that an exogenous HSA ligand, ibuprofen (IBU), exerts the analogous effect. Plasmon resonance spectroscopy data evidence that a therapeutic IBU level increases HSA affinity to monomeric Aβ40/Aβ42 by a factor of 3–5. Using thioflavin T fluorescence assay and transmission electron microcopy, we show that IBU favors the suppression of Aβ40 fibrillation by HSA. Molecular docking data indicate partial overlap between the IBU/Aβ40-binding sites of HSA. The revealed enhancement of the HSA–Aβ interaction by IBU and the strengthened inhibition of Aβ fibrillation by HSA in the presence of IBU could contribute to the neuroprotective effects of the latter, previously observed in mouse and human studies of AD

Effect of Cu\u3csup\u3e2+\u3c/sup\u3e and Zn\u3csup\u3e2+\u3c/sup\u3e Ions on Human Serum Albumin Interaction with Plasma Unsaturated Fatty Acids

Human serum albumin (HSA) serves as a depot and carrier of multiple unrelated ligands including several participants of the pathogenesis of Alzheimer\u27s disease (AD), such as amyloid β peptide (Aβ), Zn2+/Cu2+ ions, docosahexaenoic (DHA), linoleic (LA), and oleic (OA) acids. To explore the interplay between HSA interaction with Zn2+/Cu2+ and the plasma unsaturated fatty acids (DHA, LA, OA, and arachidonic acid (ArA)), we have studied the metal dependence of the fatty acid (FA) binding capacity of HSA (nmax) and structural consequences of the HSA-FA interactions. HSA loading with Zn2+ decreases nmax value by 0.3–1.5, while its saturation with Cu2+ causes the FA-dependent nmax changes by up to 0.9. The Cu2+-induced decline in nmax value for DHA is due to conformational rearrangements in HSA molecule. In other cases, the changes in nmax are attributed to steric hindarance/facilitation of the HSA-FA interaction because of the protein multimerization/monomerization, as confirmed by chemical crosslinking. The surface hydrophobicity of HSA is Cu2+-, Zn2+-, and FA-dependent and decreases upon the FA binding, according to bis-ANS fluorescence data. Overall, Zn2+ or Cu2+ binding selectively affect HSA interaction with the FAs studied, in part due to changes in quaternary structure of the protein

Intrinsically Disordered Regions in Serum Albumin: What Are They For?

Serum albumin is a major plasma protein in mammalian blood. The importance of this protein lies in its roles in both bioregulation and transport phenomena. Serum albumin binds various metal ions and participates in the transport and storage of fatty acids, bilirubin, steroids amino acids, and many other ligands, usually with regions of hydrophobic surface. Although the primary role of serum albumin is to transport various ligand, its versatile binding capacities and high concentration mean that it can assume a number of additional functions. The major goal of this article is to show how intrinsic disorder is encoded in the amino acid sequence of serum albumin, and how intrinsic disorder is related to functions of this important serum protein

Specific Cytokines of Interleukin-6 Family Interact with S100 Proteins

Cytokines of interleukin-6 (IL-6) family are important signaling proteins involved in various physiological and pathological processes. Earlier, we described interactions between IL-11 and S100P/B proteins from the family of S100 proteins engaged in the pathogenesis of numerous diseases. We probed here interactions between seven IL-6 family cytokines (IL-6, IL-11, OSM, LIF, CNTF, CT-1, and CLCF1) and fourteen S100 proteins (S100A1/A4/A6/A7/A8/A9/A10/A11/A12/A13/A14/A15/B/P). Surface plasmon resonance spectroscopy revealed formation of calcium-dependent complexes between IL-11, OSM, CNTF, CT-1, and CLCF1 and distinct subsets of S100A1/A6/B/P proteins with equilibrium dissociation constants of 19 nM – 12 µM. The existence of a network of interactions between Ca2+-loaded S100 proteins and IL-6 family cytokines suggest regulation of these cytokines by the extracellular forms of S100 proteins

Serotonin Promotes Serum Albumin Interaction with the Monomeric Amyloid β Peptide

Prevention of amyloid β peptide (Aβ) deposition via facilitation of Aβ binding to its natural depot, human serum albumin (HSA), is a promising approach to preclude Alzheimer’s disease (AD) onset and progression. Previously, we demonstrated the ability of natural HSA ligands, fatty acids, to improve the affinity of this protein to monomeric Aβ by a factor of 3 (BBRC, 510(2), 248–253). Using plasmon resonance spectroscopy, we show here that another HSA ligand related to AD pathogenesis, serotonin (SRO), increases the affinity of the Aβ monomer to HSA by a factor of 7/17 for Aβ40/Aβ42, respectively. Meanwhile, the structurally homologous SRO precursor, tryptophan (TRP), does not affect HSA’s affinity to monomeric Aβ, despite slowdown of the association and dissociation processes. Crosslinking with glutaraldehyde and dynamic light scattering experiments reveal that, compared with the TRP-induced effects, SRO binding causes more marked changes in the quaternary structure of HSA. Furthermore, molecular docking reveals distinct structural differences between SRO/TRP complexes with HSA. The disintegration of the serotonergic system during AD pathogenesis may contribute to Aβ release from HSA in the central nervous system due to impairment of the SRO-mediated Aβ trapping by HSA

The Use of Human, Bovine, and Camel Milk Albumins in Anticancer Complexes with Oleic Acid

Oleic acid (OA) is a monounsaturated fatty acid that upon binding to milk proteins, such as α-lactalbumin and lactoferrin, forms potent complexes, which exert selective anti-tumor activity against malignant cells but are nontoxic for healthy normal cells. We showed that the interaction of OA with albumins isolated from human, bovine, and camel milk results in the formation of complexes with high antitumor activity against Caco-2, HepG-2, PC-3, and MCF-7 tumor cells. The antitumor effect of the complexes is mostly due to the action of oleic acid, similar to the case of OA complexes with other proteins. Viability of tumor cells is inhibited by the albumin-OA complexes in a dose dependent manner, as evaluated by the MTT assay. Strong induction of apoptosis in tumor cells after their treatment with the complexes was monitored by flow cytometry, cell cycle analysis, nuclear staining, and DNA fragmentation methods. The complex of camel albumin with OA displayed the most pronounced anti-tumor effects in comparison with the complexes of OA with human and bovine albumins. Therefore, these results suggest that albumins have the potential to be used as efficient and low cost means of tumor treatment

Ibuprofen Favors Binding of Amyloid-β Peptide to Its Depot, Serum Albumin

The deposition of amyloid-β peptide (Aβ) in the brain is a critical event in the progression of Alzheimer’s disease (AD). This Aβ deposition could be prevented by directed enhancement of Aβ binding to its natural depot, human serum albumin (HSA). Previously, we revealed that specific endogenous ligands of HSA improve its affinity to monomeric Aβ. We show here that an exogenous HSA ligand, ibuprofen (IBU), exerts the analogous effect. Plasmon resonance spectroscopy data evidence that a therapeutic IBU level increases HSA affinity to monomeric Aβ40/Aβ42 by a factor of 3–5. Using thioflavin T fluorescence assay and transmission electron microcopy, we show that IBU favors the suppression of Aβ40 fibrillation by HSA. Molecular docking data indicate partial overlap between the IBU/Aβ40-binding sites of HSA. The revealed enhancement of the HSA–Aβ interaction by IBU and the strengthened inhibition of Aβ fibrillation by HSA in the presence of IBU could contribute to the neuroprotective effects of the latter, previously observed in mouse and human studies of AD

Interaction of S100A6 Protein with the Four-Helical Cytokines

S100 is a family of over 20 structurally homologous, but functionally diverse regulatory (calcium/zinc)-binding proteins of vertebrates. The involvement of S100 proteins in numerous vital (patho)physiological processes is mediated by their interaction with various (intra/extra)cellular protein partners, including cell surface receptors. Furthermore, recent studies have revealed the ability of specific S100 proteins to modulate cell signaling via direct interaction with cytokines. Previously, we revealed the binding of ca. 71% of the four-helical cytokines via the S100P protein, due to the presence in its molecule of a cytokine-binding site overlapping with the binding site for the S100P receptor. Here, we show that another S100 protein, S100A6 (that has a pairwise sequence identity with S100P of 35%), specifically binds numerous four-helical cytokines. We have studied the affinity of the recombinant forms of 35 human four-helical cytokines from all structural families of this fold to Ca2+-loaded recombinant human S100A6, using surface plasmon resonance spectroscopy. S100A6 recognizes 26 of the cytokines from all families of this fold, with equilibrium dissociation constants from 0.3 nM to 12 µM. Overall, S100A6 interacts with ca. 73% of the four-helical cytokines studied to date, with a selectivity equivalent to that for the S100P protein, with the differences limited to the binding of interleukin-2 and oncostatin M. The molecular docking study evidences the presence in the S100A6 molecule of a cytokine-binding site, analogous to that found in S100P. The findings argue the presence in some of the promiscuous members of the S100 family of a site specific to a wide range of four-helical cytokines. This unique feature of the S100 proteins potentially allows them to modulate the activity of the numerous four-helical cytokines in the disorders accompanied by an excessive release of the cytokines

Erythropoietin Interacts with Specific S100 Proteins

Erythropoietin (EPO) is a clinically significant four-helical cytokine, exhibiting erythropoietic, cytoprotective, immunomodulatory, and cancer-promoting activities. Despite vast knowledge on its signaling pathways and physiological effects, extracellular factors regulating EPO activity remain underexplored. Here we show by surface plasmon resonance spectroscopy, that among eighteen members of Ca2+-binding proteins of the S100 protein family studied, only S100A2, S100A6 and S100P proteins specifically recognize EPO with equilibrium dissociation constants ranging from 81 nM to 0.5 µM. The interactions occur exclusively under calcium excess. Bioinformatics analysis showed that the EPO-S100 interactions could be relevant to progression of neoplastic diseases, including cancer, and other diseases. The detailed knowledge of distinct physiological effects of the EPO-S100 interactions could favor development of more efficient clinical implications of EPO. Summing up our data with previous findings, we conclude that S100 proteins are potentially able to directly affect functional activities of specific members of all families of four-helical cytokines, and cytokines of other structural superfamilies

A Novel Approach to Bacterial Expression and Purification of Myristoylated Forms of Neuronal Calcium Sensor Proteins

N-terminal myristoylation is a common co-and post-translational modification of numerous eukaryotic and viral proteins, which affects their interaction with lipids and partner proteins, thereby modulating various cellular processes. Among those are neuronal calcium sensor (NCS) proteins, mediating transduction of calcium signals in a wide range of regulatory cascades, including reception, neurotransmission, neuronal growth and survival. The details of NCSs functioning are of special interest due to their involvement in the progression of ophthalmological and neurodegenerative diseases and their role in cancer. The well-established procedures for preparation of native-like myristoylated forms of recombinant NCSs via their bacterial co-expression with N-myristoyl transferase from Saccharomyces cerevisiae often yield a mixture of the myristoylated and non-myristoylated forms. Here, we report a novel approach to preparation of several NCSs, including recoverin, GCAP1, GCAP2, neurocalcin δ and NCS-1, ensuring their nearly complete N-myristoylation. The optimized bacterial expression and myristoylation of the NCSs is followed by a set of procedures for separation of their myristoylated and non-myristoylated forms using a combination of hydrophobic interaction chromatography steps. We demonstrate that the refolded and further purified myristoylated NCS-1 maintains its Ca2+-binding ability and stability of tertiary structure. The developed approach is generally suited for preparation of other myristoylated proteins