Interactions of soluble type II collagen with anionic polysaccharides of different molecular weight: A microthermal and molecular dynamics study

Abstract

Previously, we presented a green and efficient separation method for soluble undenatured type II collagen (SC II) based on the complex coacervation of SC II and anionic polysaccharides, and demonstrated the significant impact of molecular weight (Mw). In this study, we combined differential scanning calorimetry (DSC), microscale thermophoresis (MST) and molecular dynamics simulation (MDS) to further explore the affinity and interaction types of SC II with different anionic polysaccharides. Results showed that the denaturation temperature of SC II increased (about 3 °C) after complex coacervating with chondroitin sulfate (CS, a small anionic polysaccharide), which might be related to their strong affinity (dissociation constant of Kd and binding energy were about 3.04 × 10−6 mg/mL and −4054.97 kJ/mol, respectively), and the molecular weight of anionic polysaccharides had a greater impact than chain conformation. The non-covalent interactions between SC II and anionic polysaccharides were mainly hydrogen bonds, followed by hydrophobic interactions and ionic bonds. The hydroxyl and sulfate groups in polysaccharides could form extensive hydrogen bonds and small amount of ionic bonds with a large number of amino acids in SC II, and the hydrophobic groups such as methyl also formed hydrophobic interactions with hydrophobic parts in SC II (such as Pro82, Pro85, Val88). Importantly, the smaller the Mw of anionic polysaccharides, the faster they formed stable interactions with SC II. Therefore, anionic polysaccharides with smaller Mw had higher affinity and faster non-covalent interactions formation speed with SC II, resulting in more compact structure and higher thermal stability of the complexes.