Arginine- and Lysine-Specific Polymers for Protein Recognition and Immobilization.
Free radical polymn. of methacrylamide-based bisphosphonates turns weak arginine binders into powerful polymeric protein receptors. Dansyl-labeled homo- and copolymers with excellent water soly. are accessible through a simple copolymn. protocol. Modeling studies point to a striking structural difference between the stiff rodlike densely packed homopolymer 1 and the flexible copolymer 2 with spatially sepd. bisphosphonate units. Fluorescence titrns. in buffered aq. soln. (pH = 7.0) confirm the superior affinity of the homopolymer toward oligoarginine peptides reaching nanomolar KD values for the Tat peptide. Basic proteins are bound almost equally well by 1 and 2 with micromolar affinities, with the latter producing much more sol. complexes. The Arg selectivity of the monomer is transferred to the polymer, which binds Arg-rich proteins 1 order of magnitude tighter than lysine-rich pendants of comparable pI, size, and (Arg/Lys vs. Glu/Asp) ratio. Noncovalent deposition of both polymers on glass substrates via polyethylenimine layers results in new materials suitable for peptide and protein immobilization. RIfS measurements allow calcn. of assocn. consts. Ka as well as dissocn. kinetics kD. They generally confirm the trends already found in free soln. Close inspection of electrostatic potential surfaces suggest that basic domains favor protein binding on the flat surface. The high specificity of the bisphosphonate polymers toward basic proteins is demonstrated by comparison with polyvinyl sulfate, which has almost no effect in RIfS expts. Thus, copolymn. of few different comonomer units without crosslinking enables surface recognition of basic proteins in free soln. as well as their effective immobilization on surfaces.
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