Substrate-analog binding and electrostatic surfaces of human manganese superoxide dismutase

Jahaun Azadmanesh, Scott R. Trickel, Gloria E.O. Borgstahl

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Superoxide dismutases (SODs) are enzymes that play a key role in protecting cells from toxic oxygen metabolites by disproportionation of two molecules of superoxide into molecular oxygen and hydrogen peroxide via cyclic reduction and oxidation at the active site metal. The azide anion is a potent competitive inhibitor that binds directly to the metal and is used as a substrate analog to superoxide in studies of SOD. The crystal structure of human MnSOD-azide complex was solved and shows the putative binding position of superoxide, providing a model for binding to the active site. Azide is bound end-on at the sixth coordinate position of the manganese ion. Tetrameric electrostatic surfaces were calculated incorporating accurate partial charges for the active site in three states, including a state with superoxide coordinated to the metal using the position of azide as a model. These show facilitation of the anionic ligand to the active site pit via a ‘valley’ of positively-charged surface patches. Surrounding ridges of negative charge help guide the superoxide anion. Within the active site pit, Arg173 and Glu162 further guide and align superoxide for efficient catalysis. Superoxide coordination at the sixth position causes the electrostatic surface of the active site pit to become nearly neutral. A model for electrostatic-mediated diffusion, and efficient binding of superoxide for catalysis is presented.

Original languageEnglish (US)
Pages (from-to)68-75
Number of pages8
JournalJournal of Structural Biology
Volume199
Issue number1
DOIs
StatePublished - Jul 2017

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Keywords

  • Electrostatic guidance
  • Mitochondria
  • Reactive oxygen species
  • Superoxide dismutase enzyme
  • X-ray crystallography

ASJC Scopus subject areas

  • Structural Biology

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