Dr
Marek Ingr
(Tomas Bata University in Zlín, Faculty of Technology, Department of Physics and Materials Engineering)
Hyaluronic acid (HA, hyaluronan), an alternating co-polymer of glucuronic acid and N-acetylglucosamine ([4)-β-D-GlcpA-(1->3)-β-D-GlcpNAc-(1->]n), is a major component of extracellular matrix of animal connective tissues. It plays various roles in signaling cascades and is thus involved in inflammation, progression of various diseases including cancer, and wound healing. HA-binding proteins, hyaladherins, which serve as mediators of these processes, are both membrane-bound (CD44, LYVE-1, RHAMM) or soluble (TSG-6). TSG-6 structure is known from numerous NMR experiments that indicate its interaction with HA, heparin and chondroitinsulfate [1]. We applied the method of molecular-dynamics to study the binding of HA oligosaccharides by TSG-6 Link domain. Two binding sites were identified in a solvent constituted by pure water containing only the neutralizing counterions, one of which is identical with the HA-binding site described previously [2], but the other one, so far unknown, partially overlaps with the binding site of heparin [3] and also for chondroitinsulfate [1]. The specificity of the binding sites for HA and charged oligosaccharides in general was investigated by the comparison of HA with its neutral HA analog containing the glucuronic acid residue instead of glucose [4]. This molecule can be bound by both these sites, but the Helmholtz energies of complex dissociation determined by the umbrella sampling method show a remarkably lower stabilization of the analog in the first site, while in the other site the analog binding is even more stable than that of HA. The second binding site is thus less HA-specific and is able of binding various oligosaccharides independently of their negative charge. When NaCl is added to the solvent in the physiological concentration of 0.15 M, the binding interactions of both the ligands change. For hyaluronan the structue of both the binding modes changes considerably, but the ligand remains bound to the receptor. The neutral analog does not bind the first binding site at all, but its binding to the seco. On the contrary, this liagnd is still bound in the second binding mode is kept with only a small change in the stabilization energy. Thus, TSG-6 Link domain binds both hyaluronan and its neutral analog which indicates the possibility of designing artificial ligands with a tunable activity to hyaladherins with a potential pharmaceutical applications.
References
[1] Park, Y; Jowitt, T.A.; Day, A.J.; Prestegard, J.H. Biochemistry 2016, 55 (2), 262-276.
[2] Almond, A.; Blundell, C.D.; Higman, V.A.; MacKerell, C.D.; Day, A.J. J. Chem. Theory Comput. 2007, 3 (1), 1-16.
[3] Mahoney, D.J.; Mulloy, B.; Forster, M.J.; Blundell, C.D.; Fries, E.; Milner, C.M.; Day, A.J. J. Biol. Chem. 2005, 280 (29), 27044-27055.
[4] Ingr, M.; Kutálková, E.; Hrnčiřík, J. Carbohyd. Polym. 2017, 170, 289-295.
Summary
Hyaluronic acid (HA) is a natural polysaccharide acting as a major component of the extracellular matrix of connective tissues, which is also involved in a variety of cellular processes as a signaling molecule interacting with protein receptors. This way it plays roles in various diseases including cancer and is therefore pharmacologically interesting. In this work we use molecular dynamics to study the interactions of HA and its neutral analog with a soluble protein receptor (hyaladherin) TSG-6. This protein binds both the ligands in pure water as well as in the physiological concentration of NaCl, but the structure of the binding modes and the stability of the complexes are different depending on the solvent. Hence, this protein binds both natural and modified HA molecule, which indicates the possibility of designing its artificial ligands of tunable affinity to the receptor that may have an interesting pharmaceutical potential.
Dr
Marek Ingr
(Tomas Bata University in Zlín, Faculty of Technology, Department of Physics and Materials Engineering)
Mrs
Eva Kutálková
(Tomas Bata University in Zlín, Faculty of technology, Department of Physics and Materials Engineering, Nám. T.G. Masaryka 5555, 76001 Zlín, Czech Republic)
Mr
Josef Hrnčiřík
(Tomas Bata University in Zlín, Faculty of technology, Department of Physics and Materials Engineering, Nám. T.G. Masaryka 5555, 76001 Zlín, Czech Republic)
Mr
Roman Witasek
(Tomas Bata University in Zlín, Faculty of technology, Department of Physics and Materials Engineering, Nám. T.G. Masaryka 5555, 76001 Zlín, Czech Republic)
