Substrate-Dependent Allosteric Regulation in Cytochrome P450cam (CYP101A1).

Various biophysical methods have provided evidence of a second substrate binding site in the well-studied cytochrome P450cam, although the location and biological relevance of this site has remained elusive. A related question is how substrate and product binding and egress occurs. While many active site access channels have been hypothesized, only one, channel 1, has been experimentally validated. In this study, molecular dynamics simulations reveal an allosteric site related to substrate binding and product egress. The remote allosteric site opens channel 1 and primes the formation of a new channel that is roughly perpendicular to channel 1. Substrate entry to the active site via channel 1 as well as substrate/product egress via channel 2 is observed after binding of a second molecule of substrate to the allosteric site, indicating cooperativity between these two sites. These results are consistent with and bring together many early and recent experimental results to reveal a dynamic interplay between a weak allosteric site and substrate binding to the active site that controls P450cam activity.

Insights into an efficient light-driven hybrid P450 BM3 enzyme from crystallographic, spectroscopic and biochemical studies.

BACKGROUND: In order to perform selective CH functionalization upon visible light irradiation, Ru(II)-diimine functionalized P450 heme enzymes have been developed. The sL407C-1 enzyme containing the Ru(bpy)2PhenA (bpy=2,2'-bipyridine and PhenA=5-acetamido-1,10-phenanthroline) photosensitizer (1) covalently attached to the non-native single cysteine L407C of the P450BM3 heme domain mutant, displays high photocatalytic activity in the selective CH bond hydroxylation of several substrates. METHODS: A combination of X-ray crystallography, site-directed mutagenesis, transient absorption measurements and enzymatic assays was used to gain insights into its photocatalytic activity and electron transfer pathway. RESULTS: The crystal structure of the sL407C-1 enzyme was solved in the open and closed conformations revealing a through-space electron transfer pathway involving highly conserved, F393 and Q403, residues. Several mutations of these residues (F393A, F393W or Q403W) were introduced to probe their roles in the overall reaction. Transient absorption measurements confirm rapid electron transfer as heme reduction is observed in all four hybrid enzymes. Compared to the parent sL407C-1, photocatalytic activity was negligible in the dF393A-1 enzyme while 60% increase in activity with total turnover numbers of 420 and 90% product conversion was observed with the dQ403W-1 mutant. CONCLUSIONS: In the sL407C-1 enzyme, the photosensitizer is ideally located to rapidly deliver electrons, using the naturally occurring electron transfer pathway, to the heme center in order to activate molecular dioxygen and sustain photocatalytic activity. GENERAL SIGNIFICANCE: The results shed light on the design of efficient light-driven biocatalysts and the approach can be generalized to other members of the P450 superfamily.

Biopolymer Molecular Weight Can Modulate the Wound Healing Efficacy of Multivalent Sonic Hedgehog-Hyaluronic Acid Conjugates.

There is a clinical need for new therapeutics to improve healing of chronic impaired wounds. Thus, we investigated how biopolymer conjugation could be used to improve the wound healing performance of a key growth factor for tissue regeneration: Sonic hedgehog (Shh). We generated two multivalent Shh conjugates (mvShh) using hyaluronic acid with two different MWs, which exhibited equivalent potency and proteolytic protection in vitro. Using db/db diabetic mice, we showed that mvShh made with smaller HyA MW resulted in more rapid and robust neovascularization compared to mvShh made with larger MW HyA. Further, smaller mvShh conjugates resulted in faster wound resolution compared to the unconjugated Shh. This study is the first to show how the wound healing efficacy of multivalent protein-polymer conjugates is sensitive to the polymer MW, and our findings suggest that this parameter could be used to enhance the efficacy of growth factor conjugates.

Effector Roles of Putidaredoxin on Cytochrome P450cam Conformational States.

In this study, the effector role of Pdx (putidaredoxin) on cytochrome P450cam conformation is refined by attaching two different spin labels, MTSL or BSL (bifunctional spin-label) onto the F or G helices and using DEER (double electron-electron resonance) to measure the distance between labels. Recent EPR and crystallographic studies have observed that oxidized Pdx induces substrate-bound P450cam to change from the closed to the open state. However, this change was not observed by DEER in the reduced Pdx complex with carbon-monoxide-bound P450cam (Fe(2+)CO). In addition, recent NMR studies have failed to observe a change in P450cam conformation upon binding Pdx. Hence, resolving these issues is important for a full understanding the effector role of Pdx. Here we show that oxidized Pdx induces camphor-bound P450cam to shift from the closed to the open conformation when labeled on either the F or G helices with MTSL. BSL at these sites can either narrow the distance distribution widths dramatically or alter the extent of the conformational change. In addition, we report DEER spectra on a mixed oxidation state containing oxidized Pdx and ferrous CO-bound P450cam, showing that P450cam remains closed. This indicates that CO binding to the heme prevents P450cam from opening, overriding the influence exerted by Pdx binding. Finally, we report the open form P450cam crystal structure with substrate bound, which suggests that crystal packing effects may prevent conformational conversion. Using multiple labeling approaches, DEER provides a unique perspective to resolve how the conformation of P450cam depends on Pdx and ligand states.