Artificial Metalloenzymes: Recent Developments and Innovations in Bioinorganic Catalysis.

Cellular life is orchestrated by the biochemical components of cells that include nucleic acids, lipids, carbohydrates, proteins, and cofactors such as metabolites and metals, all of which coalesce and function synchronously within the cell. Metalloenzymes allow for such complex chemical processes, as they catalyze a myriad of biochemical reactions both efficiently and selectively, where the metal cofactor provides additional functionality to promote reactivity not readily achieved in their absence. While the past 60 years have yielded considerable insight on how enzymes catalyze these reactions, a need to engineer and develop artificial metalloenzymes has been driven not only by industrial and therapeutic needs, but also by innate human curiosity. The design of miniature enzymes, both rationally and through serendipity, using both organic and inorganic building blocks has been explored by many scientists over the years and significant progress has been made. Herein, recent developments over the past 5 years in areas that have not been recently reviewed are summarized, and prospects for future research in these areas are addressed.

Design of Artificial Glycosidases: Metallopeptides that Remove H†Antigen from Human Erythrocytes.

Catalysts that promote carbohydrate degradation have a wide range of potential applications, but the use of either enzyme glycosidases or small-molecule catalysts in biological systems raises significant challenges. Herein, we demonstrate a novel strategy for the design of synthetic agents that mimic natural glycosidases and address current problems for biological use. This strategy is illustrated by application to the development of potential blood substitutes for the rare Bombay blood type that is characterized by a deficiency of H2 antigen. Metallopeptides with 16 to 20 amino acids were constructed as artificial fucosidases that exhibit selective carbohydrate cleavage reactivity toward l-fucose over d-glucose. Selective fucose cleavage from the H2-antigen saccharide enables efficient removal of H2 antigen from erythrocytes and thereby accomplishes the conversion of regular human type-O blood into a potential blood substitute for the rare Bombay blood type.

Enhanced Synergism and Mechanism of Action Studies of Synthetic Antimicrobial Metallopeptides.

Antimicrobial peptides (AMPs) are found throughout most kingdoms of life, are an important part of host immunity, and have been shown to act synergistically in various organisms to ameliorate bacterial infections. Herein, we report the synergistic behavior observed between two AMPs, Sub5 and CP10A, against E. coli. In addition, enhanced synergistic activity against E. coli and MRSA 43300 for two derivatives of Sub5, extended with the amino-terminal copper and nickel (ATCUN) binding motif, is observed when dosed together with CP10A, while displaying little cytotoxicity towards human dermal fibroblasts. All three combinations of peptides co-localized within bacterial cells as evidenced by fluorescence confocal microscopy. Investigations into the mechanism of synergy shows that all peptides indirectly damage DNA within cells, while only the ATCUN derivatives can oxidize phospholipids. Combinations of peptides were also shown to upregulate the concentration of reactive oxygen species within both E. coli and MRSA 43300. These results suggest that the production of reactive oxygen species is an important aspect mechanistically and further highlights the potential of these metallopeptides to aid in the treatment of antibiotic-resistant infections.

Correction: Copper(ii) l/d-valine-(1,10-phen) complexes target human telomeric G-quadruplex motifs and promote site-specific DNA cleavage and cellular cytotoxicity.

Correction for 'Copper(ii) l/d-valine-(1,10-phen) complexes target human telomeric G-quadruplex motifs and promote site-specific DNA cleavage and cellular cytotoxicity' by Farukh Arjmand et al., Dalton Trans., 2020, 49, 9888-9899, DOI: 10.1039/d0dt01527j.

Copper(ii) l/d-valine-(1,10-phen) complexes target human telomeric G-quadruplex motifs and promote site-specific DNA cleavage and cellular cytotoxicity.

Chiral l-/d-valine-(1,10-phen)-Cu(ii) complexes that target G-quadruplex DNA were synthesized and thoroughly characterized by UV-vis, IR, EPR, ESI-MS, elemental analysis and single crystal X-ray spectroscopy. Complexes 1a and 1b crystallized in the monoclinic P21/c and C2 space groups, respectively. On the basis of Wolfe-Shimer analyses, the binding affinities of 1a and 1b with G-quadruplex telomeric DNA were determined, and 1a exhibited significantly higher binding as compared to 1b. Site selective cleavage of G4-DNA was demonstrated by employing the time-dependent PAGE assay, with 1a exhibiting a significantly higher cleavage rate from A1 to G22 (4.32 (±0.13) µM h-1) than 1b (4.29 (±0.11) µM h-1). The DNA cleavage profile demonstrated that both complexes perform non-random double-strand cleavage by following first-order kinetics (kobs = 0.9432 min-1 for 1a and kobs = 0.6574 min-1 for 1b). Molecular docking simulations were performed with both parallel and anti-parallel topologies of the quadruplex to provide a clear insight on G-quadruplex-complex interactions. Complexes 1a and 1b were found to interact strongly at the minor groove cavity of the quadruplex with preferential selectivity for the parallel vs. anti-parallel quadruplex. The cytotoxic activities of complexes 1a and 1b were evaluated on a few notably important human cancer cell lines, viz, breast (MCF-7), pancreatic strains (BxPC3, AsPC1) and liver (Huh7) by an MTT assay. Both 1a and 1b exhibited pronounced cytotoxic activity with remarkably low IC50 values (1-3 µM) for all tested cancer strains.