Synthetic affinity ligands as a novel tool to improve protein stability

One-Step Purification of Recombinant Cutinase from an E. coli Extract Using a Stabilizing Triazine-Scaffolded Synthetic Affinity Ligand

Cutinase from Fusarium solani pisi is an enzyme that bridges functional properties between lipases and esterases, with applications in detergents, food processing, and the synthesis of fine chemicals. The purification procedure of recombinant cutinase from E. coil extracts is a well-established but time-consuming process, which involves a sequence of two anionic exchange chromatography steps followed by dialysis. Affinity chromatography is the most efficient method for protein purification, the major limitation of its use being often the availability of a ligand selective for a given target protein. Synthetic affinity ligands that specifically recognize certain sites on the surface of proteins are highly desirable for affinity processes due to their cost-effectiveness, durability, and reusability across multiple cycles. Additionally, these ligands establish moderate affinity interactions with the target protein, making it possible to purify proteins under gentle conditions while maintaining high levels of activity recovery. This study aimed to develop a new method for purifying cutinase, utilizing triazine-scaffolded biomimetic affinity ligands. These ligands were previously screened from a biased-combinatorial library to ensure their binding ability to cutinase without compromising its biological function. A lead ligand, designated as 11/3', [4-({4-chloro-6-[(2-methylbutyl)amino]-1,3,5-triazin-2-yl}amino)benzoic acid], was chosen and directly synthesized onto agarose. Experiments conducted at different scales demonstrated that this ligand (with an affinity constant Ka ≈ 104 M-1) exhibited selectivity towards cutinase, enabling the purification of the enzyme from an E. coli crude production medium in a single step. Under optimized conditions, the protein and activity yields reached 25% and 90%, respectively, with a resulting cutinase purity of 85%.

Biomimetic Affinity Ligands for Protein Purification

The development of sophisticated molecular modeling software and new bioinformatic tools, as well as the emergence of data banks containing detailed information about a huge number of proteins, enabled the de novo intelligent design of synthetic affinity ligands. Such synthetic compounds can be tailored to mimic natural biological recognition motifs or to interact with key surface-exposed residues on target proteins, and are designated as "biomimetic ligands". A well-established methodology for generating biomimetic or synthetic affinity ligands integrates rational design with combinatorial solid-phase synthesis and screening, using the triazine scaffold and analogs of amino acid side chains to create molecular diversity.Triazine-based synthetic ligands are nontoxic, low-cost, and highly stable compounds that can replace advantageously natural biological ligands in the purification of proteins by affinity-based methodologies.

Biomimetic affinity ligands for protein purification

The development of sophisticated molecular modeling software and new bioinformatic tools, as well as the emergence of data banks containing detailed information about a huge number of proteins, enabled the de novo intelligent design of synthetic affinity ligands. Such synthetic compounds can be tailored to mimic natural biological recognition motifs or to interact with key surface-exposed residues on target proteins and are designated as "biomimetic ligands." A well-established methodology for generating biomimetic or synthetic affinity ligands integrates rational design with combinatorial solid-phase synthesis and screening, using the triazine scaffold and analogues of amino acids side chains to create molecular diversity.Triazine-based synthetic ligands are nontoxic, low-cost, highly stable compounds that can replace advantageously natural biological ligands in the purification of proteins by affinity-based methodologies.

Computational design of a thermostable mutant of cocaine esterase via molecular dynamics simulations

Cocaine esterase (CocE) has been known as the most efficient native enzyme for metabolizing naturally occurring cocaine. A major obstacle to the clinical application of CocE is the thermoinstability of native CocE with a half-life of only ∼11 min at physiological temperature (37 °C). It is highly desirable to develop a thermostable mutant of CocE for therapeutic treatment of cocaine overdose and addiction. To establish a structure-thermostability relationship, we carried out molecular dynamics (MD) simulations at 400 K on wild-type CocE and previously known thermostable mutants, demonstrating that the thermostability of the active form of the enzyme correlates with the fluctuation (characterized as the root-mean square deviation and root-mean square fluctuation of atomic positions) of the catalytic residues (Y44, S117, Y118, H287, and D259) in the simulated enzyme. In light of the structure-thermostability correlation, further computational modelling including MD simulations at 400 K predicted that the active site structure of the L169K mutant should be more thermostable. The prediction has been confirmed by wet experimental tests showing that the active form of the L169K mutant had a half-life of 570 min at 37 °C, which is significantly longer than those of the wild-type and previously known thermostable mutants. The encouraging outcome suggests that the high-temperature MD simulations and the structure-thermostability relationship may be considered as a valuable tool for the computational design of thermostable mutants of an enzyme.