Effect of oxidation rate on cross-linking of mussel adhesive proteins.
The cross-linking behavior of mussel adhesive protein Mefp-1 was studied by measuring the rate of aggregation of the protein by photon correlation spectroscopy. To be able to calculate the aggregation numbers, the hydrodynamic radius of monomer Mefp-1 (10 nm) was determined under reducing conditions. The aggregation is controlled by the redox potential of the solution, and the aggregation number varied, independent of pH, over a factor 2 within the experimentally accessible redox potential window. A kinetic model for cross-linking, based on the intricate interplay of the oxidation and auto-oxidation of the hydroquinones of Mefp-1, is proposed. The oxidation rate strongly depends on redox potential. The cross-linking rate is taken to be proportional to the rate of auto-oxidation. The model correctly predicts the experimentally observed phenomena. When the oxidation rate is slower than the auto-oxidation rate, cross-linking is efficient and controlled by the oxidation rate. When the rate of auto-oxidation rate is slower than the oxidation rate, the cross-linking is inefficient due to the quick exhaustion of the hydroquinones. The experimentally determined rate constant for cross-linking is found to be much smaller than those found for auto-oxidation of hydroquinones because of the excluded volume interactions imposed by the protein backbone. Tuning the interplay between oxidation and auto-oxidation presents the potential of controlling cross-linking density independent of the density of reactive groups.
Laboratory of Physical Chemistry, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands. s.haemers@iri.tudelft.nl
Sander
S
Haemers
Ger J M
GJ
Koper
Gert
G
Frens
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D049872:Bivalvia / Q000737:chemistry* / Q000502:physiology; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*
D003432:Cross-Linking Reagents; D011506:Proteins; C037403:adhesive protein, mussel