Recognition of granulocyte-macrophage colony-stimulating factor by specific S100 proteins

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic myelopoietic growth factor and proinflammatory cytokine, clinically used for multiple indications and serving as a promising target for treatment of many disorders, including cancer, multiple sclerosis, rheumatoid arthritis, psoriasis, asthma, COVID-19. We have previously shown that dimeric Ca2+-bound forms of S100A6 and S100P proteins, members of the multifunctional S100 protein family, are specific to GM-CSF. To probe selectivity of these interactions, the affinity of recombinant human GM-CSF to dimeric Ca2+-loaded forms of 18 recombinant human S100 proteins was studied by surface plasmon resonance spectroscopy. Of them, only S100A4 protein specifically binds to GM-CSF with equilibrium dissociation constant, Kd, values of 0.3-2 μM, as confirmed by intrinsic fluorescence and chemical crosslinking data. Calcium removal prevents S100A4 binding to GM-CSF, whereas monomerization of S100A4/A6/P proteins disrupts S100A4/A6 interaction with GM-CSF and induces a slight decrease in S100P affinity for GM-CSF. Structural modelling indicates the presence in the GM-CSF molecule of a conserved S100A4/A6/P-binding site, consisting of the residues from its termini, helices I and III, some of which are involved in the interaction with GM-CSF receptors. The predicted involvement of the 'hinge' region and F89 residue of S100P in GM-CSF recognition was confirmed by mutagenesis. Examination of S100A4/A6/P ability to affect GM-CSF signaling showed that S100A4/A6 inhibit GM-CSF-induced suppression of viability of monocytic THP-1 cells. The ability of the S100 proteins to modulate GM-CSF activity is relevant to progression of various neoplasms and other diseases, according to bioinformatics analysis. The direct regulation of GM-CSF signaling by extracellular forms of the S100 proteins should be taken into account in the clinical use of GM-CSF and development of the therapeutic interventions targeting GM-CSF or its receptors.

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.

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.

Interferon Beta Activity Is Modulated via Binding of Specific S100 Proteins

Interferon-β (IFN-β) is a pleiotropic cytokine used for therapy of multiple sclerosis, which is also effective in suppression of viral and bacterial infections and cancer. Recently, we reported a highly specific interaction between IFN-β and S100P lowering IFN-β cytotoxicity to cancer cells (Int J Biol Macromol. 2020; 143: 633–639). S100P is a member of large family of multifunctional Ca²⁺-binding proteins with cytokine-like activities. To probe selectivity of IFN-β—S100 interaction with respect to S100 proteins, we used surface plasmon resonance spectroscopy, chemical crosslinking, and crystal violet assay. Among the thirteen S100 proteins studied S100A1, S100A4, and S100A6 proteins exhibit strictly Ca²⁺-dependent binding to IFN-β with equilibrium dissociation constants, K_d, of 0.04–1.5 µM for their Ca²⁺-bound homodimeric forms. Calcium depletion abolishes the S100—IFN-β interactions. Monomerization of S100A1/A4/A6 decreases K_d values down to 0.11–1.0 nM. Interferon-α is unable of binding to the S100 proteins studied. S100A1/A4 proteins inhibit IFN-β-induced suppression of MCF-7 cells viability. The revealed direct influence of specific S100 proteins on IFN-β activity uncovers a novel regulatory role of particular S100 proteins, and opens up novel approaches to enhancement of therapeutic efficacy of IFN-β.

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 Са²⁺-binding ability and stability of tertiary structure. The developed approach is generally suited for preparation of other myristoylated proteins.

Effect of Cu2+ and Zn2+ 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's 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 (n_max) and structural consequences of the HSA-FA interactions. HSA loading with Zn²⁺ decreases n_max value by 0.3-1.5, while its saturation with Cu²⁺ causes the FA-dependent n_max changes by up to 0.9. The Cu²⁺-induced decline in n_max value for DHA is due to conformational rearrangements in HSA molecule. In other cases, the changes in n_max 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.

The binding of monomeric amyloid β peptide to serum albumin is affected by major plasma unsaturated fatty acids

Human serum albumin (HSA) serves as a natural depot of amyloid β peptide (Aβ). Improvement of Aβ binding to HSA should impede Alzheimer's disease (AD). We developed a method for quantitation of the interaction between monomeric Aβ40/42 and HSA using surface plasmon resonance spectroscopy. The dissociation constant of HSA complex with recombinant Aβ40/42 is 0.2-0.3 μM. Flemish variant of Aβ40 has 2.5-10-fold higher affinity to HSA. The parameters of the HSA-Aβ interaction are selectively sensitive to HSA binding of major plasma unsaturated fatty acids and Cu²⁺. Linoleic and arachidonic acids promote the HSA-Aβ42 interaction. The developed methodology for quantitation of HSA-Aβ interaction may serve as a tool for search of compounds favoring HSA-Aβ interaction, thereby preventing AD progression.

Modulation of linoleic acid-binding properties of human serum albumin by divalent metal cations

Human serum albumin (HSA) is an abundant multiligand carrier protein, linked to progression of Alzheimer's disease (AD). Blood HSA serves as a depot of amyloid β (Aβ) peptide. Aβ peptide-buffering properties of HSA depend on interaction with its ligands. Some of the ligands, namely, linoleic acid (LA), zinc and copper ions are involved into AD progression. To clarify the interplay between LA and metal ion binding to HSA, the dependence of LA binding to HSA on Zn²⁺, Cu²⁺, Mg²⁺ and Ca²⁺ levels and structural consequences of these interactions have been explored. Seven LA molecules are bound per HSA molecule in the absence of the metal ions. Zn²⁺ binding to HSA causes a loss of one bound LA molecule, while the other metals studied exert an opposite effect (1-2 extra LA molecules are bound). In most cases, the observed effects are not related to the metal-induced changes in HSA quaternary structure. However, the Zn²⁺-induced decline in LA capacity of HSA could be due to accumulation of multimeric HSA forms. Opposite to Ca²⁺/Mg²⁺-binding, Zn²⁺ or Cu²⁺ association with HSA induces marked changes in its hydrophobic surface. Overall, the divalent metal ions modulate LA capacity and affinity of HSA to a different extent. LA- and Ca²⁺-binding to HSA synergistically support each other. Zn²⁺ and Cu²⁺ induce more pronounced changes in hydrophobic surface and quaternary structure of HSA and its LA capacity. A misbalanced metabolism of these ions in AD could modify interactions of HSA with LA, other fatty acids and hydrophobic substances, associated with AD.

[Is cobalt-binding capacity of serum a new perspective diagnostic marker?]

The aim of this study was to determine the reference interval of serum cobalt-binding capacity (CoBC) and to estimate the effect of factors unrelated to oxidative modification of serum albumin on this diagnostic marker. A group of healthy volunteers (n=194), a group of patients with autoimmune diseases (n=44) and a group of patients with diabetes type 2 (n=50) participated in this study. The regional reference interval was found to be 0,462-0,744 mmol Co 2+ /l of serum. The study of serum CoBC in two groups of patients showed that the CoBC level strongly depends on the serum protein profile. Therefore, this diagnostic test may be used for diagnosing ischemia, but other pathologies associated with changes in a ratio of blood protein fractions can also influence the serum CoBC level.