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Molecular-Level Understanding of Protein Adsorption at the Interface between Water and a Strongly Interacting Uncharged Solid Surface
journal contribution
posted on 2015-12-17, 01:32 authored by Matthew
J. Penna, Milan Mijajlovic, Mark J. BiggsAlthough protein adsorption on solids
is of immense relevance,
experimental limitations mean there is still a remarkable lack of
understanding of the adsorption mechanism, particularly at a molecular
level. By subjecting 240+ molecular dynamics simulations of two peptide/water/solid
surface systems to statistical analysis, a generalized molecular level
mechanism for peptide adsorption has been identified for uncharged
surfaces that interact strongly with the solution phase. This mechanism
is composed of three phases: (1) biased diffusion of the peptide from
the bulk phase toward the surface; (2) anchoring of the peptide to
the water/solid interface via interaction of a hydrophilic group with
the water adjacent to the surface or a strongly interacting hydrophobic
group with the surface; and (3) lockdown of the peptide on the surface
via a slow, stepwise and largely sequential adsorption of its residues,
which we term ‘statistical zippering’. The adsorption
mechanism is dictated by the existence of water layers adjacent to
the solid and orientational ordering therein. By extending the solid
into the solution by ∼8 Å and endowing it with a charged
character, the water layers ensure the peptide feels the effect of
the solid at a range well beyond the dispersion force that arises
from it, thus inducing biased diffusion from afar. The charging of
the interface also facilitates anchoring of the peptide near the surface
via one of its hydrophilic groups, allowing it time it would otherwise
not have to rearrange and lockdown. Finally, the slowness of the lockdown
process is dictated by the need for the peptide groups to replace
adjacent tightly bound interfacial water.