Collagen Structured Hydration

Collagen is a triple-helical protein unique to the extracellular matrix, conferring rigidity and stability to tissues such as bone and tendon. For the [(PPG)10]3 collagen-mimetic peptide at room temperature, our molecular dynamics simulations show that these properties result in a remarkably ordered first hydration layer, of water molecules hydrogen-bonded to the backbone-carbonyl (bb-CO) oxygen atoms. This originates from the following observations. The radius of gyration attests that the PPG triplets are organized along a straight line, so that all triplets (excepting the ends) are equivalent. The solvent accessible surface area (SASA) for the bb-CO oxygens shows a repetitive regularity for every triplet. This leads to bb-CO⋯HOH occupancy following a similar regularity, similar also to the crystal-phase 0-2-1 water occupancy in the P-P-G triplet. The regularity is maintained in spite of the sub-nsec water exchange rate, because the bb-CO sites rarely remain vacant. The manifested ordered first-shell water molecules are expected to produce a cylindrical electrostatic potential around the peptide, that might guide cation diffusion in its vicinity.