title: Adsorption of the intrinsically disordered saliva protein histatin 5 to silica surfaces. A Monte Carlo simulation and ellipsometry study.
abstract: OBJECTIVE
  The adsorption of histatin 5 to hydrophilic silica surfaces is governed by electrostatic attractive forces between the positive protein and the negative surface. Hence pH and ionic strength control the adsorbed amount, which can be described by coarse-grained Monte Carlo simulations accounting for electrostatic forces and charge regulation of the protein.
  
  
  METHODS
  The amount of histatin 5 adsorbed to hydrophilic silica surfaces at different pH and ionic strengths was measured using null ellipsometry. The results were compared with coarse-grained Monte Carlo simulations of a single histatin 5 molecule and a surface with a fixed, smeared charge set according to experimental values for silica. The Langmuir isotherm was used to calculate the surface coverage from the simulation results. The effect of charge regulation of the protein was investigated.
  
  
  RESULTS
  Even though electrostatic attractive forces are important for the investigated system, a non-electrostatic short-ranged attraction with a strength of about 2.9kBT per amino acid was needed in the simulations to get surface coverages close to experimental values. The importance of electrostatics increases with increasing pH. Charge regulation of the protein affected the results from the simulations only at high surface charge and low ionic strength.
authors.affiliation: Division of Theoretical Chemistry, Lund University, P.O.B. 124, SE-221 00 Lund, Sweden. Electronic address: kristin.hyltegren@teokem.lu.se.
authors.forename: Kristin
authors.initials: K
authors.lastname: Hyltegren
authors.affiliation: Division of Physical Chemistry, Lund University, P.O.B. 124, SE-221 00 Lund, Sweden.
authors.forename: Tommy
authors.initials: T
authors.lastname: Nylander
authors.affiliation: Division of Theoretical Chemistry, Lund University, P.O.B. 124, SE-221 00 Lund, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Lund
authors.affiliation: Division of Theoretical Chemistry, Lund University, P.O.B. 124, SE-221 00 Lund, Sweden.
authors.forename: Marie
authors.initials: M
authors.lastname: Skepö
mesh_terms: D000327:Adsorption; D054808:Histatins / Q000737:chemistry*; D006801:Humans; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D010316:Particle Size; D012463:Saliva / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013057:Spectrum Analysis; D013499:Surface Properties
chemical_list: C068075:HTN3 protein, human; D054808:Histatins; D012822:Silicon Dioxide
keywords: Adsorption; Charge regulation; Coarse graining; Ellipsometry; Histatin 5; Intrinsically disordered proteins; Monte Carlo simulations