Chemokines from a Structural Perspective Miller, Michelle C; Mayo, Kevin H
International journal of molecular sciences,
10/2017, Letnik:
18, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Chemokines are a family of small, highly conserved cytokines that mediate various biological processes, including chemotaxis, hematopoiesis, and angiogenesis, and that function by interacting with ...cell surface G-Protein Coupled Receptors (GPCRs). Because of their significant involvement in various biological functions and pathologies, chemokines and their receptors have been the focus of therapeutic discovery for clinical intervention. There are several sub-families of chemokines (e.g., CXC, CC, C, and CX3C) defined by the positions of sequentially conserved cysteine residues. Even though all chemokines also have a highly conserved, three-stranded β-sheet/α-helix tertiary structural fold, their quarternary structures vary significantly with their sub-family. Moreover, their conserved tertiary structures allow for subunit swapping within and between sub-family members, thus promoting the concept of a "chemokine interactome". This review is focused on structural aspects of CXC and CC chemokines, their functional synergy and ability to form heterodimers within the chemokine interactome, and some recent developments in structure-based chemokine-targeted drug discovery.
Extra- and intra-cellular activity occurs under the direction of numerous inter-molecular interactions, and in any tissue or cell, molecules are densely packed, thus promoting those molecular ...interactions. Galectins and chemokines, the focus of this review, are small, protein effector molecules that mediate various cellular functions—in particular, cell adhesion and migration—as well as cell signaling/activation. In the past, researchers have reported that combinations of these (and other) effector molecules act separately, yet sometimes in concert, but nevertheless physically apart and via their individual cell receptors. This view that each effector molecule functions independently of the other limits our thinking about functional versatility and cooperation, and, in turn, ignores the prospect of physiologically important inter-molecular interactions, especially when both molecules are present or co-expressed in the same cellular environment. This review is focused on such protein-protein interactions with chemokines and galectins, the homo- and hetero-oligomeric structures that they can form, and the functional consequences of those paired interactions.
Galectins are a family of small, highly conserved, molecular effectors that mediate various biological processes, including chemotaxis and angiogenesis, and that function by interacting with various ...cell surface glycoconjugates, usually targeting β-galactoside epitopes. Because of their significant involvement in various biological functions and pathologies, galectins have become a focus of therapeutic discovery for clinical intervention against cancer, among other pathological disorders. In this review, we focus on understanding galectin structure-function relationships, their mechanisms of action on the molecular level, and targeting them for therapeutic intervention against cancer.
Chemokines and galectins are simultaneously upregulated and mediate leukocyte recruitment during inflammation. Until now, these effector molecules have been considered to function independently. ...Here, we tested the hypothesis that they form molecular hybrids. By systematically screening chemokines for their ability to bind galectin‐1 and galectin‐3, we identified several interacting pairs, such as CXCL12 and galectin‐3. Based on NMR and MD studies of the CXCL12/galectin‐3 heterodimer, we identified contact sites between CXCL12 β‐strand 1 and Gal‐3 F‐face residues. Mutagenesis of galectin‐3 residues involved in heterodimer formation resulted in reduced binding to CXCL12, enabling testing of functional activity comparatively. Galectin‐3, but not its mutants, inhibited CXCL12‐induced chemotaxis of leukocytes and their recruitment into the mouse peritoneum. Moreover, galectin‐3 attenuated CXCL12‐stimulated signaling via its receptor CXCR4 in a ternary complex with the chemokine and receptor, consistent with our structural model. This first report of heterodimerization between chemokines and galectins reveals a new type of interaction between inflammatory mediators that can underlie a novel immunoregulatory mechanism in inflammation. Thus, further exploration of the chemokine/galectin interactome is warranted.
Synopsis
Chemokines and galectins are simultaneously upregulated during inflammation and mediate leukocyte recruitment. A systematic screen now demonstrates their physical interaction as heterodimers, identifying several novel interacting pairs.
Chemokines and galectins can engage in cross talk by pairing, as exemplified by galectin‐3 and CXCL12.
The association of CXCL12 with galectin‐3 appears to have potential for modulating chemokine activity.
Galectin‐3 inhibits CXCL12‐induced chemotaxis of leukocytes and their recruitment to inflammation sites.
Galectin‐3 attenuates CXCL12‐stimulated signaling via its receptor CXCR4 in a ternary complex.
Chemokines and galectins are simultaneously upregulated during inflammation and mediate leukocyte recruitment. A systematic screen now demonstrates their physical interaction as heterodimers, identifying several novel interacting pairs.
•Two pectic polysaccharides were purified from Radix Sophorae Tonkinensis.•They both contained HG, RG-I and RG-II domains with different mass ratios.•RG-I domains in them varied in Mw, degree of ...branching and side chain structures.•They had different antioxidant activities toward scavenging of different radicals.•HG domain rich in GalA might be the key factor for antioxidant activity of pectin.
Two pectic polysaccharides (WRSP-A2b and WRSP-A3a) have been obtained from Radix Sophorae Tonkinensis and comparatively investigated in terms of their physical properties and antioxidant activities. Monosaccharide composition, FT-IR, NMR and enzymatic analyses indicate that both WRSP-A2b (13.6 kDa) and WRSP-A3a (44.6 kDa) consist of homogalacturonan (HG), rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II) domains, with mass ratios of 0.9:1.8:1 and 2.3:2.9:1, respectively. The RG-I domains were further purified and characterized. Results show that WRSP-A2b contains a highly branched RG-I domain, primarily substituted with α-(1→5)-linked arabinans, whereas WRSP-A3a contains a small branched RG-I domain mainly composed of β-(1→4)-linked galactan side chains. WRSP-A3a exhibits stronger antioxidant activity in scavenging different radicals than WRSP-A2b, a finding that may be due to its higher content of GalA residues and HG domains. Our results provide useful information for screening natural polysaccharide-based antioxidants from Radix Sophorae Tonkinensis.
Commercially-supplied potato galactan (PG) is widely used as a model polysaccharide in various bioactivity studies. However, results using this galactan are not always consistent with the stated ...composition. Here, we assessed its composition by fractionating this commercial PG and purified its primary components: PG-A, PG-B and PG-Cp with weight-averaged molecular weights of 430, 93, and 11.3 kDa, respectively. PG-Cp consists of free β-1,4-galactan chains, whereas PG-A and PG-B are type I rhamnogalacturonans with long β-1,4-galactan side chains of up to 80 Gal residues and short β-1,4-galactan side chains of 0 to 3 Gal residues that display a “trees in lawn” pattern. Structures of these polysaccharides correlate well with their activities in terms of galectin-3 binding and gut bacterial growth assays. Our study clarifies the confusion related to commercial PG, with purified fractions serving as better model polysaccharides in bioactivity investigations.
Display omitted
•Commercial potato galactan was separated into sub-fractions PG-A, PG-B and PG-Cp.•PG-Cp consists of free β-1,4-galactan chains.•PG-A and PG-B are RG-I type polysaccharides with β-1,4-galactan side chains.•Their structures were characterized and a “trees in lawn” model is proposed.•Purified PG fractions are better model substances for structure-activity studies.
Aggregation of amyloid‐β peptide 1–42 (Aβ42) initiates the onset of Alzheimer's disease (AD), and all the drugs designed to attenuate AD have failed in clinical trials. Emodin reduces levels of ...β‐amyloid, tau aggregation, oxidative stress, and inflammatory response, demonstrating AD therapeutic potential, whereas its effect on the accumulation of the amyloid‐β protein is not well understood. In this work, we investigated emodin activity on Aβ aggregation using a range of biochemical, biophysical, and cell‐based approaches. We provide evidence to suggest that emodin blocks Aβ42 fibrillogenesis and Aβ‐induced cytotoxicity, displaying a greater effect than that of curcumin. Through adopting three short peptides (Aβ1‐16, Aβ17‐33, and Aβ28‐42), it was proven that emodin interacts with the Leu17‐Gly33 sequence. Furthermore, our findings indicated that Val18 and Phe19 in Aβ42 are the target residues with which emodin interacts according amino acid mutation experiments. When fed to 8‐month‐old B6C3‐Tg mice for 2 months, high‐dose emodin ameliorates cognitive impairment by 60%–70%. Pathological results revealed that levels of Aβ deposition in the brains of AD mice treated with a high dose of emodin decreased by 50%–70%. Therefore, our study indicates that emodin may represent a promising drug for AD treatment.
We find emodin inhibits Aβ42 aggregation: Emodin blocks Aβ42 fibrillogenesis and Aβ‐induced cytotoxicity through interacting with Val18 and Phe19. High‐dose emodin greatly ameliorates cognitive impairment and the levels of cerebral Aβ deposition in Alzheimer's disease mice. Therefore, our study indicates that emodin may represent a promising drug for the treatment of Alzheimer's disease.
The structure of human galectin-16 (Gal-16) has yet to be solved, and its function has remained elusive.
X-ray crystallography was used to determine the atomic structures of Gal-16 and two of its ...mutants. The Gal-16 oligomer state was investigated by gel filtration, its hemagglutination activity was determined along with its ability to bind lactose using ITC. The cellular distribution of EGFP-tagged Gal-16 in various cell lines was also investigated, and the interaction between Gal-16 and c-Rel was assessed by pull-down studies, microscale thermophoresis and immunofluorescence.
Unlike other galectins, Gal-16 lacks the ability to bind the β-galactoside lactose. Lactose binding could be regained by replacing an arginine (Arg55) with asparagine, as shown in the crystal structures of two lactose-loaded Gal-16 mutants (R55N and R55N/H57R). Gal-16 was also shown to be monomeric by gel filtration, as well as in crystal structures. Thus, this galectin could not induce erythrocyte agglutination. EGFP-tagged Gal-16 was found to be localized mostly in the nucleus of various cell types, and can interact with c-Rel, a member of NF-κB family.
Gal-16 exists as a monomer and its ligand binding is significantly different from that of other prototype galectins, suggesting that it has a novel function(s). The interaction between Gal-16 and c-Rel indicates that Gal-16 may regulate signal transduction pathways via the c-Rel hub in B or T cells at the maternal-fetal interface.
The present study lays the foundation for further studies into the cellular and physiological functions of Gal-16.
•Gal-16 is a monomeric protein that is different from dimeric prototype galectins.•Gal-16 has a pseudo ligand binding site that cannot bind to β-galactosides.•Gal-16 is mostly distributed in the cell nucleus.•Gal-16 can interact with NF-κB family member c-Rel.
Linear β-manno-oligosaccharides (l-β-MOS) are widely used to investigate oligo- and poly-saccharide structures and mannanolytic enzyme activities. l-β-MOS are also being used as prebiotic agents with ...potential bio-active properties. In this study, we developed an efficient protocol to prepare a series of l-β-MOS by hydrolyzing cassia gum (CG) using mannanolytic enzymes (endo-1,4-β-mannanase, α-galactosidases and β-glucosidases). By using medium pressure liquid chromatography (MPLC), we purified l-β-MOS with different degrees of polymerization (DPs). HPAEC-PAD, MALDI-TOF-MS and NMR studies confirmed that these l-β-MOS species ranged from 1,4-β-d-mannobiose to 1,4-β-d-mannononaose (DP 2–9) with >95% purity. Our results provide a robust approach to preparing l-β-MOS, thus enabling l-β-MOS to be further used in the fields of chemistry, life science, and nutritional food.
Display omitted
•An efficient protocol for preparing l-β-MOS was investigated.•l-β-MOS purified were analyzed by HPAEC, MS and 13C NMR.•High purity 1,4-β-d-mannobiose to 1,4-β-d-mannononaose (DP 2–9) were obtained.
PDF
