Large-Size Subunit Catalases Are Chimeric Proteins: A H2O2 Selecting Domain with Catalase Activity Fused to a Hsp31-Derived Domain Conferring Protein Stability and Chaperone Activity

High-Throughput Screening Method Using Escherichia coli Keio Mutants for Assessing Primary Damage Mechanism of Antimicrobials

The Escherichia coli Keio mutant collection has been a tool for assessing the role of specific genes and determining their role in E. coli physiology and uncovering novel functions. In this work, specific mutants in the DNA repair pathways and oxidative stress response were evaluated to identify the primary targets of silver nanoparticles (NPs) and their mechanism of action. The results presented in this work suggest that NPs mainly target DNA via double-strand breaks and base modifications since the recA, uvrC, mutL, and nfo mutants rendered the most susceptible phenotype, rather than involving the oxidative stress response. Concomitantly, during the establishment of the control conditions for each mutant, the katG and sodA mutants showed a hypersensitive phenotype to mitomycin C, an alkylating agent. Thus, we propose that KatG catalase plays a key role as a cellular chaperone, as reported previously for the filamentous fungus Neurospora crassa, a large subunit catalase. The Keio collection mutants may also be a key tool for assessing the resistance mechanism to metallic NPs by using their potential to identify novel pathways involved in the resistance to NPs.

The Molecular Chaperone Mechanism of the C-Terminal Domain of Large-Size Subunit Catalases

Large-size subunit catalases (LSCs) have an additional C-terminal domain (CT) that is structurally similar to Hsp31 and DJ-1 proteins, which have molecular chaperone activity. The CT of LSCs derives from a bacterial Hsp31 protein. There are two CT dimers with inverted symmetry in LSCs, one dimer in each pole of the homotetrameric structure. We previously demonstrated the molecular chaperone activity of the CT of LSCs. Like other chaperones, LSCs are abundant proteins that are induced under stress conditions and during cell differentiation in bacteria and fungi. Here, we analyze the mechanism of the CT of LSCs as an unfolding enzyme. The dimeric form of catalase-3 (CAT-3) CT (TDC3) of Neurospora crassa presented the highest activity as compared to its monomeric form. A variant of the CAT-3 CT lacking the last 17 amino acid residues (TDC3Δ17aa), a loop containing hydrophobic and charged amino acid residues only, lost most of its unfolding activity. Substituting charged for hydrophobic residues or vice versa in this C-terminal loop diminished the molecular chaperone activity in all the mutant variants analyzed, indicating that these amino acid residues play a relevant role in its unfolding activity. These data suggest that the general unfolding mechanism of CAT-3 CT involves a dimer with an inverted symmetry, and hydrophobic and charged amino acid residues. Each tetramer has four sites of interaction with partially unfolded or misfolded proteins. LSCs preserve their catalase activity under different stress conditions and, at the same time, function as unfolding enzymes.

Catalases in the pathogenesis of Sporothrix schenckii research

Pathogenic fungal infection success depends on the ability to escape the immune response. Most strategies for fungal infection control are focused on the inhibition of virulence factors and increasing the effectiveness of antifungal drugs. Nevertheless, little attention has been focused on their physiological resistance to the host immune system. Hints may be found in pathogenic fungi that also inhabit the soil. In nature, the saprophyte lifestyle of fungi is also associated with predators that can induce oxidative stress upon cell damage. The natural sources of nutrients for fungi are linked to cellulose degradation, which in turn generates reactive oxygen species (ROS). Overall, the antioxidant arsenal needed to thrive both in free-living and pathogenic lifestyles in fungi is fundamental for success. In this review, we present recent findings regarding catalases and oxidative stress in fungi and how these can be in close relationship with pathogenesis. Additionally, special focus is placed on catalases of Sporothrix schenckii as a pathogenic model with a dual lifestyle. It is assumed that catalase expression is activated upon exposure to H₂O₂, but there are reports where this is not always the case. Additionally, it may be relevant to consider the role of catalases in S. schenckii survival in the saprophytic lifestyle and why their study can assess their involvement in the survival and therefore, in the virulence phenotype of different species of Sporothrix and when each of the three catalases are required. Also, studying antioxidant mechanisms in other isolates of pathogenic and free-living fungi may be linked to the virulence phenotype and be potential therapeutic and diagnostic targets. Thus, the rationale for this review to place focus on fungal catalases and their role in pathogenesis in addition to counteracting the effect of immune system reactive oxygen species. Fungi that thrive in soil and have mammal hosts could shed light on the importance of these enzymes in the two types of lifestyles. We look forward to encouraging more research in a myriad of areas on catalase biology with a focus on basic and applied objectives and placing these enzymes as virulence determinants.

Discovering Diverse Roles of Peroxidases and Catalases in Photosynthetic and Non-Photosynthetic Eukaryotes

This Special Issue of Antioxidants, dedicated to "The Role of Peroxidases and Catalases in Photosynthetic and Non-photosynthetic Eukaryotes", was accomplished with the contribution of five original research articles and two detailed reviews [...].

Monofunctional Heme-Catalases

The review focuses on four issues that are critical for the understanding of monofunctional catalases. How hydrogen peroxide (H2O2) reaches the active site and outcompetes water molecules to be able to function at a very high rate is one of the issues examined. Part of the answer is a gate valve system that is instrumental to drive out solvent molecules from the final section of the main channel. A second issue relates to how the enzyme deals with an unproductive reactive compound I (Cpd I) intermediate. Peroxidatic two and one electron donors and the transfer of electrons to the active site from NADPH and other compounds are reviewed. The new ascribed catalase reactions are revised, indicating possible measurement pitfalls. A third issue concerns the heme b to heme d oxidation, why this reaction occurs only in some large-size subunit catalases (LSCs), and the possible role of singlet oxygen in this and other modifications. The formation of a covalent bond between the proximal tyrosine with the vicinal residue is analyzed. The last issue refers to the origin and function of the additional C-terminal domain (TD) of LSCs. The TD has a molecular chaperone activity that is traced to a gene fusion between a Hsp31-type chaperone and a small-size subunit catalase (SSC).