The role of S126 in the Staphylococcus equorum MnSOD activity and stability

New Insights into the Cooperativity and Dynamics of Dimeric Enzymes

A survey of protein databases indicates that the majority of enzymes exist in oligomeric forms, with about half of those found in the UniProt database being homodimeric. Understanding why many enzymes are in their dimeric form is imperative. Recent developments in experimental and computational techniques have allowed for a deeper comprehension of the cooperative interactions between the subunits of dimeric enzymes. This review aims to succinctly summarize these recent advancements by providing an overview of experimental and theoretical methods, as well as an understanding of cooperativity in substrate binding and the molecular mechanisms of cooperative catalysis within homodimeric enzymes. Focus is set upon the beneficial effects of dimerization and cooperative catalysis. These advancements not only provide essential case studies and theoretical support for comprehending dimeric enzyme catalysis but also serve as a foundation for designing highly efficient catalysts, such as dimeric organic catalysts. Moreover, these developments have significant implications for drug design, as exemplified by Paxlovid, which was designed for the homodimeric main protease of SARS-CoV-2.

Introducing Intermolecular Interaction to Strengthen the Stability of MnSOD Dimer

Manganese superoxide dismutase from Staphylococcus equorum (MnSODSeq) maintains its activity upon treatments like a wide range of pH, addition of detergent and denaturing agent, exposure to ultraviolet light, and heating up to 50 °C. The enzyme dimer dissociates at 52-55 °C, while its monomer unfolds at 63-67 °C. MnSOD dimeric form is indispensable for the enzyme activity; therefore, strengthening the interactions between the monomers is the most preferred strategy to improve the enzyme stability. However, to date, modification of MnSODSeq at the dimer interface has been unfruitful despite excluding the inner and outer sphere regions that are important to the enzyme activity. Here, a new strategy was developed and K38R-A121E/Y double substitutions were proposed. These mutants displayed similar enzyme activity to the wild type. K38R-A121E dimer was thermally more stable and its monomer stability was similar to the wild type. The thermal stability of K38R-A121Y dimer was similar to the wild type but its monomer was thermally less stable. In addition, the structure of the previously reported L169W mutant was also elucidated. The L169W mutant structure showed that intramolecular modification can decrease flexibility of the MnSODSeq monomer and leads to a less stable enzyme with similar activity to the wild type. Thus, while the enzyme activity depends on arrangement of residues in the dimer interface, the stability appears to depend more on its monomeric architecture. Furthermore, in the L169W structure in complex with azide, which is a specific inhibitor for MnSOD, one of the azide molecules was present in the dimer interface region that previously has been identified to involve in the enzymatic reaction. Nevertheless, the present results show that an MnSODSeq mutant with better thermal stability has been obtained.

The structure-function relationships and physiological roles of MnSOD mutants

In this review, we focus on understanding the structure–function relationships of numerous manganese superoxide dismutase (MnSOD) mutants to investigate the role that various amino acids play to maintain enzyme quaternary structure or the active site structure, catalytic potential and metal homeostasis in MnSOD, which is essential to maintain enzyme activity. We also observe how polymorphisms of MnSOD are linked to pathologies and how post-translational modifications affect the antioxidant properties of MnSOD. Understanding how modified forms of MnSOD may act as tumor promoters or suppressors by altering the redox status in the body, ultimately aid in generating novel therapies that exploit the therapeutic potential of mutant MnSODs or pave the way for the development of synthetic SOD mimics.