Direct detection of coupled proton and electron transfers in human manganese superoxide dismutase
Year: 2021
Type: article
Abstract: Human manganese superoxide dismutase is a critical oxidoreductase found in the mitochondrial matrix. Concerted proton and electron transfers are used by the enzyme to rid the mitochondria of O 2 •− . The mechanisms of concerted transfer enzymes are typically unknown due to the difficulties in detecting the protonation states of specific residues and solvent molecules at particular redox states. Here, neutron diffraction of two redox-controlled manganese superoxide dismutase crystals reveal the all-atom structures of Mn 3+ and Mn 2+ enzyme forms. The structures deliver direct data on protonation changes between oxidation states of the metal. Observations include glutamine deprotonation, the involvement of tyrosine and histidine with altered pK a s, and four unusual strong-short hydrogen bonds, including a low barrier hydrogen bond. We report a concerted proton and electron transfer mechanism for human manganese superoxide dismutase from the direct visualization of active site protons in Mn 3+ and Mn 2+ redox states.
Source: Nature Communications
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $5,560
Funders: U.S. Department of Energy, National Aeronautics and Space Administration, Nuclear Safety and Security Commission, National Institutes of Health, Office of Science, Fred and Pamela Buffett Cancer Center, National Cancer Institute, National Institute of General Medical Sciences, National Center for Research Resources, Basic Energy Sciences, Biological and Environmental Research, Office of Experimental Program to Stimulate Competitive Research, Oak Ridge National Laboratory
Awards: Nebraska Research Network in Functional Genomics, G1663022414, G281700398, SUPEROXIDE DISMUTASES (SODS) ARE IMPORTANT ANTIOXIDANT ENZYMES THAT PROTECT ALL MVING CELLS AGAINST TOXIC OXYGEN METABOLITES, ALSO KNOWN AS REACTIVE, G3418376741, Computational Tools for Neutron Protein Crystallography, SUPEROXIDE DISMUTASES (SODS) ARE IMPORTANT ANTIOXIDANT ENZYMES THAT PROTECT ALL LIVING CELLS AGAINST TOXIC OXYGEN METABOLITES ALSO KNOWN AS REACTIVE OXYGEN SPECIES (ROS). SODS ARE THE FIRST DEFENSE AGAINST PROPAGATION OF DAMAGING OXIDATIVE REACTIONS THROUGH ELIMINATION OF SUPEROXIDE. SUPEROXIDE IS GENERATED THROUGH NORMAL METABOLISM AND/OR IONIZING RADIATION. EACH CATALYTIC CYCLE DISMUTES TWO MOLECULES OF SUPEROXIDE TO OXYGEN AND HYDROGEN PEROXIDE VIA CYCLIC REDUCTION AND OXIDATION HALF REACTIONS USING THE ACTIVE SITE METAL ION. HUMANS HAVE CU/ZNSOD IN THE CYTOSOL AND EXTRACELLULAR SPACES AND MNSOD IN THEIR MITOCHONDRIA. MUTATIONS IN SOD LEAD TO AGING AND DEGENERATIVE DISEASES SUCH AS AMYOTROPHIC LATERAL SCLEROSIS DIABETES AND CANCER. THIS FLIGHT PROPOSAL WILL PROVIDE THE CRITICAL CRYSTAL SAMPLES NEEDED FOR A DETAILED STUDY OF HUMAN SOD. DESPITE THE BIOLOGICAL AND MEDICAL IMPORTANCE OF SOD THE COMPLETE ENZYMATIC MECHANISM IS STILL UNKNOWN. PRECISE STRUCTURAL DATA ARE NEEDED. THE BINDING SITES OF THE DIATOMIC SUBSTRATE AND PRODUCT AS WELL AS THE SOURCE OF THE PROTONS IN THE REACTION HAVE BEEN STUDIED BUT THEIR EXACT IDENTIFICATION HAS NOT BEEN POSSIBLE. THIS DETAILED INFORMATION CAN ONLY BE DETERMINED BY NEUTRON DIFFRACTION. COMPLEXES OF HUMAN MNSOD INCLUDING STRUCTURAL INTERMEDIATES AND MUTANTS WILL BE THE TARGETS FOR LARGE VOLUME CRYSTAL ( 1MM3) GROWTH FOR STRUCTURE DETERMINATION BY NEUTRON MACROMOLECULAR CRYSTALLOGRAPHY (NMC). THE QUIESCENT ENVIRONMENT AFFORDED BY MICROGRAVITY IS KNOWN TO GROW CRYSTALS LARGE ENOUGH FOR NEUTRON STUDIES NOT ONLY ARE THEY LARGE BUT THEIR QUALITY APPROACHES PERFECTION. IN 2001 THE BORGSTAHL LABORATORY SUCCESSFULLY GREW LARGE CRYSTALS OF SOD USING MICROGRAVITY CONDITIONS ON THE INTERNATIONAL SPACE STATION (ISS). WITH NASA S RENEWED INTEREST IN IMPLEMENTING THE MICROGRAVITY ENVIRONMENT ON THE ISS FOR PROTEIN CRYSTAL GROWTH WE WOULD LIKE TO MOVE FORWARD WITH THESE EXCITING EARLY MICROGRAVITY CRYSTALLIZATION RESULTS FOR SOD. EXISTING CRYSTALLIZATION HARDWARE THAT USES THE GRANADA CRYSTALLIZATION BOXES (GCB) FOR CAPILLARY COUNTERDIFFUSION PROTOCOLS WILL BE USED TO ACHIEVE THESE GOALS. A MICROGRAVITY ENVIRONMENT IS ESSENTIAL TO FORM A STABLE SUPERSATURATION GRADIENT TO OBTAIN THE LARGE HIGH QUALITY CRYSTALS REQUIRED FOR NMC. THEN NMC WILL BE PERFORMED WITH COLLABORATORS AT OAK RIDGE NATIONAL LABORATORY (ORNL). THE PRINCIPAL OUTCOME WILL BE TO IDENTIFY THE ROLE OF HYDROGEN ATOMS IN ENZYMATIC ACTIVITY DISCERN SUPEROXIDE FROM PEROXIDE AND WATER FROM HYDROXIDE ION BY THEIR PROTONATION STATE AND DECIPHER A STRUCTURE-BASED MECHANISM FOR HUMAN MNSOD MORE PRECISELY THAN FROM PREVIOUS X-RAY CRYSTALLOGRAPHIC MODELS DETERMINED FROM EARTH-GROWN CRYSTALS. THESE CONTRIBUTIONS WILL ALSO PROVIDE CRITERIA NEEDED FOR THE PROTEIN ENGINEERING OF DESIRABLE PROPERTIES INTO ENZYMATIC METAL CENTERS FOR PROTON COUPLED ELECTRON TRANSFER., Nebraska Research Network in Functional Genomics, G8070519185, Deciphering the Enzymatic Mechanism of Superoxide Dismutase, Buffett Cancer Center Support Grant
OpenAlex ID: W3141831396