title: Detergent-protein interactions in aqueous buffer suspensions of Photosystem I (PS I).
abstract: Systematic and uniform monolayer formation of Photosystem I (PS I) onto self-assembled monolayer (SAM) substrates to enable unidirectional electron transfer is crucial for its successful use in the fabrication of bio-hybrid solid-state electronic or photovoltaic devices. Yet, our recent studies (Mukherjee et al., 2010) indicate that surface self-assembly of PS I from aqueous buffer suspensions onto alkanethiolate SAM/Au substrates frequently leads to complex columnar structures due to solution phase protein aggregations. We investigate the effect of two prototypical non-ionic detergents, n-Dodecyl-β-D-Maltoside (DM) and Triton X-100 (TX-100), on protein-protein interactions via the protein-detergent interfacial chemistry. Dynamic light scattering (DLS) experiments are used to demonstrate the impact of relative protein/detergent concentrations on aggregation dynamics of PS I suspensions. In turn, the surface attachment characteristics of PS I adsorbed from the aforementioned suspensions onto SAM/Au substrate is examined by atomic force (AFM) microscopy. Our results indicate that relative concentration of PS I and detergents (DM or, TX-100) with respect to their critical micelle concentrations (CMC) determines the extent of self-association between PS I complexes driven by the screening induced by detergent micelles and/or, inter-protein distances. Such interfacial phenomena during the PS I-detergent complexation process drives the colloidal system through various regimes of phase separations, suspension and/or, de-aggregation, wherein individual PS I complexes can exist in a frustrated state that prevents favorable orientations for PS I-PS I interactions. The present study presents a novel strategy, heretofore not considered, for tailoring inter-protein distances and protein-protein interactions in solution phase, thereby allowing a superior control on the surface attachment of PS I onto SAM/Au substrates.
authors.affiliation: Sustainable Energy Education and Research Center (SEERC), University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: Dibyendu
authors.initials: D
authors.lastname: Mukherjee
authors.forename: Mark
authors.initials: M
authors.lastname: May
authors.forename: Bamin
authors.initials: B
authors.lastname: Khomami
mesh_terms: D003902:Detergents / Q000737:chemistry*; D005960:Glucosides; D008823:Micelles; D017830:Octoxynol; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry*; D013535:Suspensions / Q000737:chemistry
chemical_list: D003902:Detergents; D005960:Glucosides; D008823:Micelles; D045331:Photosystem I Protein Complex; D011506:Proteins; D013535:Suspensions; C040358:dodecyl maltoside; D017830:Octoxynol