Many processes associated with DNA synthesis and repair, involve metal-containing cofactors, and misregulation of these processes can lead to carcinogenesis. However, because of the paucity of biochemical and structural information, knowledge of their modi operandi or the molecular linkage between integrity of the metallocofactor and pathological events remain largely unknown. A particularly important class of metal cofactors is that of iron-sulfur [Fe-S] clusters, perhaps the most ubiquitous prosthetic groups in nature. Their abundance is likely the consequence of their structural and redox plasticity, thereby making them versatile and tunable cofactors for mediating electron transfer. However, [Fe-S]-cluster containing proteins are much more functionally versatile than that originally thought; they mediate and participate in a variety of cellular processes, such as DNA maintenance, amino acid and nucleotide metabolism, ribosome function and tRNA modification. [Fe-S] clusters participate in enzyme catalysis and bind substrates, regulate gene expression, act as sensors of small molecules (i.e. O2, NO), store iron, serve as sulfur donors during synthesis of lipoic acid and biotin, etc. Thus, despite the simplicity of their chemical ‘make-up’, their chemical and functional diversity is both astounding and complex.
Many viral proteins are intrinsically disordered and often annotated as non structural proteins. These comprise elemental components of viruses, such as Sars-Cov2, PRRSV, Hepatitis, etc. for the viruses to replicate and efficiently infect the host. Many of these proteins contain conserved cysteines and histidines that can act as ligands for metallocofactors, such as Zn and [Fe-S] clusters. In fact, many of these proteins have been annotated as Zinc Finger proteins, because they contain a variable CCCH motif. Our research demonstrates that many of these proteins can in addition accomodate an [Fe-S] cofactor, the latter of which in many cases is the physiological cofactor. We have embarged onto a functional and structural journey to indentify such proteins and characterize their cofactors. The outcomes of this research will have many implications for the treatment of viral-related diseases and developement of therapeutic targets.
HD proteins are omnipresent and belong to a superfamily of metalloenzymes counting presently > 137,000 members with diverse and unknown functions affecting the human health and environment, including HIV-1 immunoresponse, anti-virulence, DNA/RNA unwinding and degradation, and signaling. Whereas their initial functionality was predicted to be solely hydrolytic, novel diiron oxygenases have emerged carrying out chemically difficult small molecule activations.
These proteins are typified by a helical fold harboring the H…HD…D residue quartet, known to bind a divalent metal ion (most commonly Zn2+). The presence of two additional histidines inbetween the aspartate residues extends their metal binding capacity and supports formation of di- or even tri-nuclear clusters. Though members of this superfamily were originally annotated as (phospho)hydrolases, less than a decade ago, a diiron HD enzyme involved in the catabolism of inositol associated with type I diabetes mellitus, namely myo-inositol oxygenase (MIOX) was demonstrated to carry out a radically different reaction using molecular oxygen to afford transformation of its substrate. The only recently recognized HD enzyme PhnZ, was also shown to follow the paradigm of MIOX, employing oxygen for the acquisition of phosphate from an organophosphonate by marine microorganisms. Biochemically uncharacterized dinuclear HD domain proteins have been selected as targets for discovering their substrates, identifying key residues that favor hydrolase or oxygenase activity and examining the catalytic potency of the types of metals incorporated. Considering the emergence of MIOX and PhnZ as evolutionary means to carry out reactions affecting the human health and environment, as well as the emergence of hydrolytic HD enzymes orchestrating immunoresponse in eukaryotes and prokaryotes, our work aims to serve as a paradigm for discovering new antiviral (and therapeutic) factors and functions within the largely uncharacterized HD superfamily.