Mahy, J.-P.

Eur. J. Biochem. 1998, 257, 121-130, 10.1046/j.1432-1327.1998.2570121.x

The topology of the binding site has been studied for two monoclonal antibodies 13G10 and 14H7, elicited against iron(III)‐α,α,α,β‐meso‐tetrakis(ortho‐carboxyphenyl)porphyrin {α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin]}, and which exhibit in the presence of this α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] cofactor a peroxidase activity. A comparison of the dissociation constants of the complexes of 13G10 and 14H7 with various tetra‐aryl‐substituted porphyrin has shown that : (a) the central iron(III) atom of α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] is not recognized by either of the two antibodies; and (b) the ortho‐carboxylate substituents of the meso‐phenyl rings of α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] are essential for the recognition of the porphyrin by 13G10 and 14H7. Measurement of the dissociation constants for the complexes of 13G10 and 14H7 with the four atropoisomers of (o‐COOHPh)4‐porphyrinH2 as well as mono‐ and di‐ortho‐carboxyphenyl‐substituted porphyrins suggests that the three carboxylates in the α, α, β position are recognized by both 13G10 and 14H7 with the two in the α, β positions more strongly bound to the antibody protein. Accordingly, the topology of the active site of 13G10 and 14H7 has roughly two‐thirds of the α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] cofactor inserted into the binding site of the antibodies, with one of the aryl ring remaining outside. Three of the carboxylates are bound to the protein but no amino acid residue acts as an axial ligand to the iron atom. Chemical modification of lysine, histidine, tryptophan and arginine residues has shown that only modification of arginine residues causes a decrease in both the binding of α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] and the peroxidase activity of both antibodies. Consequently, at least one of the carboxylates of the hapten is bound to an arginine residue and no amino acids such as lysine, histidine or tryptophan participate in the catalysis of the heterolytic cleavage of the O‐O bond of H2O2. In addition, the amino acid sequence of both antibodies not only reveals the presence of arginine residues, which could be those involved in the binding of the carboxylates of the hapten, but also the presence of several amino acids in the complementary determining regions which could bind other carboxylates through a network of H bonds.

Keinan, E.

J. Am. Chem. Soc. 1999, 121, 8978-8982, 10.1021/ja990314q

An antibody−metalloporphyrin assembly that catalyzes the enantioselective oxidation of aromatic sulfides to sulfoxides is presented. Antibody SN37.4 was elicited against a water-soluble tin(IV) porphyrin containing an axial α-naphthoxy ligand. The catalytic assembly comprising antibody SN37.4 and a ruthenium(II) porphyrin cofactor exhibited typical enzyme characteristics, such as predetermined oxidant and substrate selectivity, enantioselective delivery of oxygen to the substrate, and Michaelis−Menten saturation kinetics. This assembly, which promotes a complex, multistep catalytic event, represents a close model of natural heme-dependent oxidation enzymes.

Tiede, D.M.; Utschig, L.M.

J. Am. Chem. Soc. 2011, 133, 16334-16337, 10.1021/ja206012r

Solar energy conversion of water into the environmentally clean fuel hydrogen offers one of the best long-term solutions for meeting future energy demands. Nature provides highly evolved, finely tuned molecular machinery for solar energy conversion that exquisitely manages photon capture and conversion processes to drive oxygenic water-splitting and carbon fixation. Herein, we use one of Nature’s specialized energy-converters, the Photosystem I (PSI) protein, to drive hydrogen production from a synthetic molecular catalyst comprised of inexpensive, earth-abundant materials. PSI and a cobaloxime catalyst self-assemble, and the resultant complex rapidly produces hydrogen in aqueous solution upon exposure to visible light. This work establishes a strategy for enhancing photosynthetic efficiency for solar fuel production by augmenting natural photosynthetic systems with synthetically tunable abiotic catalysts.

Tiede, D.M.; Utschig, L.M.

J. Am. Chem. Soc. 2013, 135, 13246-13249, 10.1021/ja405277g

The direct conversion of sunlight into fuel is a promising means for the production of storable renewable energy. Herein, we use Nature’s specialized photosynthetic machinery found in the Photosystem I (PSI) protein to drive solar fuel production from a nickel diphosphine molecular catalyst. Upon exposure to visible light, a self-assembled PSI-[Ni(P2PhN2Ph)2](BF4)2 hybrid generates H2 at a rate 2 orders of magnitude greater than rates reported for photosensitizer/[Ni(P2PhN2Ph)2](BF4)2 systems. The protein environment enables photocatalysis at pH 6.3 in completely aqueous conditions. In addition, we have developed a strategy for incorporating the Ni molecular catalyst with the native acceptor protein of PSI, flavodoxin. Photocatalysis experiments with this modified flavodoxin demonstrate a new mechanism for biohybrid creation that involves protein-directed delivery of a molecular catalyst to the reducing side of Photosystem I for light-driven catalysis. This work further establishes strategies for constructing functional, inexpensive, earth-abundant solar fuel-producing PSI hybrids that use light to rapidly produce hydrogen directly from water.