Computational de novo design and characterization of a protein that selectively binds a highly hyperpolarizable abiological chromophore.
This work reports the first example of a single-chain protein computationally designed to contain four α-helical segments and fold to form a four-helix bundle encapsulating a supramolecular abiological chromophore that possesses exceptional nonlinear optical properties. The 109-residue protein, designated SCRPZ-1, binds and disperses an insoluble hyperpolarizable chromophore, ruthenium(II) [5-(4'-ethynyl-(2,2';6',2″-terpyridinyl))-10,20-bis(phenyl)porphinato]zinc(II)-(2,2';6',2″-terpyridine)(2+) (RuPZn) in aqueous buffer solution at a 1:1 stoichiometry. A 1:1 binding stoichiometry of the holoprotein is supported by electronic absorption and circular dichroism spectra, as well as equilibrium analytical ultracentrifugation and size exclusion chromatography. SCRPZ-1 readily dimerizes at micromolar concentrations, and an empirical redesign of the protein exterior produced a stable monomeric protein, SCRPZ-2, that also displayed a 1:1 protein:cofactor stoichiometry. For both proteins in aqueous buffer, the encapsulated cofactor displays photophysical properties resembling those exhibited by the dilute RuPZn cofactor in organic solvent: femtosecond, nanosecond, and microsecond time scale pump-probe transient absorption spectroscopic data evince intensely absorbing holoprotein excited states having large spectral bandwidth that penetrate deep in the near-infrared energy regime; the holoprotein electronically excited triplet state exhibits a microsecond time scale lifetime characteristic of the RuPZn chromophore. Hyper-Rayleigh light scattering measurements carried out at an incident irradiation wavelength of 1340 nm for these holoproteins demonstrate an exceptional dynamic hyperpolarizabilty (β1340 = 3100 × 10(-30) esu). X-ray reflectivity measurements establish that this de novo-designed hyperpolarizable protein can be covalently attached with high surface density to a silicon surface without loss of the cofactor, indicating that these assemblies provide a new approach to bioinspired materials that have unique electro-optic functionality.
Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
H Christopher
HC
Fry
Andreas
A
Lehmann
Louise E
LE
Sinks
Inge
I
Asselberghs
Andrey
A
Tronin
Venkata
V
Krishnan
J Kent
JK
Blasie
Koen
K
Clays
William F
WF
DeGrado
Jeffery G
JG
Saven
Michael J
MJ
Therien
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003198:Computer Simulation; D015195:Drug Design; D008665:Metalloporphyrins / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry* / Q000235:genetics; D013379:Substrate Specificity
D008665:Metalloporphyrins; D011506:Proteins; C553738:ruthenium(II) (5-(4'-ethynyl-(2,2'-6',2''-terpyridinyl))-10,20-bis(phenyl)porphinato)zinc(II)-(2,2'-6',2''-terpyridine)