Allosteric Cooperation in a De Novo-Designed Two-Domain Protein
Proc. Natl. Acad. Sci. U.S.A. 2020, 117, 33246-33253, 10.1073/pnas.2017062117
We describe the de novo design of an allosterically regulated protein, which comprises two tightly coupled domains. One domain is based on the DF (Due Ferri in Italian or two-iron in English) family of de novo proteins, which have a diiron cofactor that catalyzes a phenol oxidase reaction, while the second domain is based on PS1 (Porphyrin-binding Sequence), which binds a synthetic Zn-porphyrin (ZnP). The binding of ZnP to the original PS1 protein induces changes in structure and dynamics, which we expected to influence the catalytic rate of a fused DF domain when appropriately coupled. Both DF and PS1 are four-helix bundles, but they have distinct bundle architectures. To achieve tight coupling between the domains, they were connected by four helical linkers using a computational method to discover the most designable connections capable of spanning the two architectures. The resulting protein, DFP1 (Due Ferri Porphyrin), bound the two cofactors in the expected manner. The crystal structure of fully reconstituted DFP1 was also in excellent agreement with the design, and it showed the ZnP cofactor bound over 12 Å from the dimetal center. Next, a substrate-binding cleft leading to the diiron center was introduced into DFP1. The resulting protein acts as an allosterically modulated phenol oxidase. Its Michaelis–Menten parameters were strongly affected by the binding of ZnP, resulting in a fourfold tighter Km and a 7-fold decrease in kcat. These studies establish the feasibility of designing allosterically regulated catalytic proteins, entirely from scratch.
Anchoring strategy: Amino acidOptimization: ---Reaction: 4-amino-phenol oxidationMax TON: 10ee: ---PDB: 7JH6Notes: diFe-DFP3: Km 2.9 mM, kcat 0.7 min-1, 10 turnovers for 1 mM substrate, 20 uM protein. On binding ZnP, Km decreased 4x, and kcat decreased 7x, resulting in a lower kcat/Km overall.
Alteration of the Oxygen-Dependent Reactivity of De Novo Due Ferri Proteins
Nat. Chem. 2012, 4, 900-906, 10.1038/NCHEM.1454
De novo proteins provide a unique opportunity to investigate the structure–function relationships of metalloproteins in a minimal, well-defined and controlled scaffold. Here, we describe the rational programming of function in a de novo designed di-iron carboxylate protein from the Due Ferri family. Originally created to catalyse the O2-dependent, two-electron oxidation of hydroquinones, the protein was reprogrammed to catalyse the selective N-hydroxylation of arylamines by remodelling the substrate access cavity and introducing a critical third His ligand to the metal-binding cavity. Additional second- and third-shell modifications were required to stabilize the His ligand in the core of the protein. These structural changes resulted in at least a 106-fold increase in the relative rate between the arylamine N-hydroxylation and hydroquinone oxidation reactions. This result highlights the potential for using de novo proteins as scaffolds for future investigations of the geometric and electronic factors that influence the catalytic tuning of di-iron active sites.
Reaction: N-HydroxylationMax TON: ---ee: ---PDB: 2LFDNotes: ---
An Artificial Di-Iron Oxo-Orotein with Phenol Oxidase Activity
Nat. Chem. Biol. 2009, 5, 882-884, 10.1038/nchembio.257
Here we report the de novo design and NMR structure of a four-helical bundle di-iron protein with phenol oxidase activity. The introduction of the cofactor-binding and phenol-binding sites required the incorporation of residues that were detrimental to the free energy of folding of the protein. Sufficient stability was, however, obtained by optimizing the sequence of a loop distant from the active site.
Reaction: Alcohol oxidationMax TON: >50ee: ---PDB: 2KIKNotes: kcat/KM ≈ 1380 M-1*min-1
Reaction: Amine oxidationMax TON: ---ee: ---PDB: 2KIKNotes: kcat/KM ≈ 83 M-1*min-1
De Novo Design of Catalytic Proteins
Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 11566-11570, 10.1073/pnas.0404387101
The de novo design of catalytic proteins provides a stringent test of our understanding of enzyme function, while simultaneously laying the groundwork for the design of novel catalysts. Here we describe the design of an O2-dependent phenol oxidase whose structure, sequence, and activity are designed from first principles. The protein catalyzes the two-electron oxidation of 4-aminophenol (k cat/K M = 1,500 M·1·min·1) to the corresponding quinone monoimine by using a diiron cofactor. The catalytic efficiency is sensitive to changes of the size of a methyl group in the protein, illustrating the specificity of the design.
Reaction: Alcohol oxidationMax TON: >100ee: ---PDB: ---Notes: kcat/KM ≈ 1540 M-1*min-1
De Novo Design of Four-Helix Bundle Metalloproteins: One Scaffold, Diverse Reactivities
Acc. Chem. Res. 2019, 10.1021/acs.accounts.8b00674
De novo protein design represents anattractive approach for testing and extending our under-standing of metalloprotein structure and function. Here, we describe our work on the design of DF (Due Ferri or two-ironin Italian), a minimalist model for the active sites of muchlarger and more complex natural diiron and dimanganeseproteins. In nature, diiron and dimanganese proteins protypi-cally bind their ions in 4-Glu, 2-His environments, and theycatalyze diverse reactions, ranging from hydrolysis, to O2-dependent chemistry, to decarbonylation of aldehydes. In the design of DF, the position of each atom including the backbone, the first-shell ligands, the second-shell hydrogen-bonded groups, and the well-packed hydrophobic core was bespoke using precise mathematical equations and chemical principles. The first member of the DF family was designed to be of minimal size and complexity and yet to display the quintessential elements required for binding the dimetal cofactor. After thoroughly characterizing its structural, dynamic, spectroscopic, and functional properties, we added additional complexity in a rational stepwise manner to achieve increasingly sophisticated catalytic functions, ultimately demonstrating substrate-gated four-electron reduction of O2to water. We also briefly describe the extension of these studies to the design of proteins that bind non biological metal cofactors (a synthetic porphyrin and a tetranuclear cluster), and a Zn2+/proton antiporting membrane protein. Together these studies demonstrate a successful and generally applicable strategy for de novo metalloprotein design, which might indeed mimic the process by which primordial metalloproteins evolved. We began the design process with a highly symmetrical backbone and binding site, by using point-group symmetry to assemble the secondary structures that position the amino acid side chains required for binding. The resulting models provided a rough starting point and initial parameters for the subsequent precise design of thefinal protein using modern methods of computational protein design. Unless the desired site is itself symmetrical, this process requires reduction of the symmetry or lifting it altogether. Nevertheless, the initial symmetrical structure can be helpful to restrain the search space during assembly of the backbone. Finally, the methods described here should be generally applicable to the design of highly stable and robust catalysts and sensors. There is considerable potential in combining the efficiency and knowledge base associated with homogeneous metal catalysis with the programmability, biocompatibility, and versatility of proteins. While the work reported here focuses on testing and learning the principles of natural metalloproteins by designing and studying proteins one at a time, there is also considerable potential for using designed proteins that incorporate both biological and non biological metal ion cofactors for the evolution of novel catalysts.
Optimization: Computational designNotes: Additional PDB: 1LT1