title: Immobilization of the enzyme beta-lactamase on biotin-derivatized poly(L-lysine)-g-poly(ethylene glycol)-coated sensor chips: a study on oriented attachment and surface activity by enzyme kinetics and in situ optical sensing.
abstract: Understanding the conformation, orientation, and specific activity of proteins bound to surfaces is crucial for the development and optimization of highly specific and sensitive biosensors. In this study, the very efficient enzyme beta-lactamase is used as a model protein. The wild-type form was genetically engineered by site-directed mutagenesis to introduce single cysteine residues on the surface of the enzyme. The cysteine thiol group is subsequently biotinylated with a dithiothreitol (DTT)-cleavable biotinylation reagent. beta-Lactamase is then immobilized site-specifically via the biotin group on neutral avidin-covered surfaces with the aim to control the orientation of the enzyme molecule at the surface and study its effect on enzymatic activity using Nitrocefin as the substrate. The DTT-cleavable spacer allows the release of the specifically bound enzyme from the surface. Immobilization of the enzyme is performed on a monolayer of the polycationic, biotinylated polymer PLL-g-PEG/PEG-biotin assembled on niobium oxide (Nb2O5) surfaces via neutral avidin as the docking site. Two different assembly protocols, the sequential adsorption of avidin and biotinylated beta-lactamase and the immobilization of preformed complexes of beta-lactamase and avidin, are compared in terms of immobilization efficiency. In situ optical waveguide lightmode spectroscopy and colorimetric analysis of enzymatic activity were used to distinguish between specific and unspecific enzyme adsorption, to sense quantitatively the amount of immobilized enzyme, and to determine Michaelis-Menten kinetics. All tested enzyme variants turned out to be active upon immobilization at the polymeric surface. However, the efficiency of immobilized enzymes relative to the soluble enzymes was reduced about sevenfold, mainly because of impaired substrate (Nitrocefin) diffusion or restricted accessibility of the active site. No significant effect of different enzyme orientations could be detected, probably because the enzymes were attached to the surface through long, flexible PEG chain linkers.
authors.affiliation: BiointerfaceGroup, Laboratory for Surface Science and Technology, Department of Materials, Swiss Federal Institute of Technology (ETH) Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
authors.forename: Guoliang
authors.initials: G
authors.lastname: Zhen
authors.forename: Verena
authors.initials: V
authors.lastname: Eggli
authors.forename: Janos
authors.initials: J
authors.lastname: Vörös
authors.forename: Prisca
authors.initials: P
authors.lastname: Zammaretti
authors.forename: Marcus
authors.initials: M
authors.lastname: Textor
authors.forename: Rudi
authors.initials: R
authors.lastname: Glockshuber
authors.forename: Eva
authors.initials: E
authors.lastname: Kuennemann
mesh_terms: D000327:Adsorption; D015374:Biosensing Techniques / Q000379:methods*; D001710:Biotin / Q000737:chemistry*; D004800:Enzymes, Immobilized / Q000737:chemistry*; D007700:Kinetics; D009556:Niobium / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D010316:Particle Size; D011092:Polyethylene Glycols / Q000138:chemical synthesis / Q000737:chemistry*; D011107:Polylysine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012680:Sensitivity and Specificity; D013499:Surface Properties; D013997:Time Factors; D001618:beta-Lactamases / Q000737:chemistry*
chemical_list: D004800:Enzymes, Immobilized; D010087:Oxides; C443714:polylysine-graft-(poly(ethylene glycol)); D009556:Niobium; D011107:Polylysine; D011092:Polyethylene Glycols; D001710:Biotin; D001618:beta-Lactamases; C073337:niobium pentoxide