Role of Water in Mediating the Interaction Between Collagens
Collagens are triple-helical molecules that self-assemble into higher order fibers forming the major component of extracellular matrix. We had previously reported the role of the first hydration layer in controlling the conformational behavior of the collagen triple helix. Here we perform explicit-water molecular dynamics simulations to elucidate the structural features of water in mediating the interaction between collagen triple helices (PDB ID: 1A3I, 2D3F). By dividing the simulation box
... cells, we quantified local water density, diffusion coefficient, and water orientation at atomistic resolution. Around a single collagen triple helix the reduction in diffusion coefficient and density fluctuation extend up to 11 Angstroms from the collagen backbone, and the circumferential and radial orientation of water near hydrophobic and hydrophilic groups, respectively, were clearly distinguishable. When two triple helices were held at a radial separation that is a few Angstroms larger than their crystalline packing distance, water in between them had reduced diffusion coefficient and constrained angular orientation. This indicates that the experimentally observed attractive force between collagens at small distances may have an entropic origin. We also tested three-collagen systems where one collagen is radially translated from its original position in the crystal packing by 4 or 7 Angstroms, and found that it moves towards the other two within 3-ns of simulation, nearly restoring the crystal packing. These results illustrate the microscopic origins of water mediated attraction between collagen molecules.