Premium
Effects of Hydrogen Bond Donors on Reactivity of Sulfite Oxidase
Author(s) -
Bali Sofia
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.655.33
Subject(s) - sulfite oxidase , chemistry , active site , sulfite , pyridinium , half reaction , molybdenum , rate determining step , nucleophile , inorganic chemistry , reaction mechanism , medicinal chemistry , catalysis , stereochemistry , combinatorial chemistry , redox , organic chemistry
Sulfite oxidase (SO) catalyzes the conversion of sulfite to sulfate as the last step in the degradation of cysteine and methionine [1]. Severe neonatal neurological problems are caused by SO deficiency in humans [2]. The overall mechanism of SO suggested that the reductive half reaction of SO is the rate limiting step for enzyme activity [3]. Using a computational approach, first I will study the elementary steps for the half reaction to determine the rate limiting step, then by introducing mutations in the active site of SO I will determine the effects of the hydrogen donors present in the active site. SO is part of the Molybdenum cofactor family of enzymes as it contains a mononuclear Molybdenum (Mo) that is penta‐coordinated [4]. At the Mo active site, the reductive half reaction of sulfite to sulfate takes place in two steps. The first step is a nucleophilic attack by the sulfite ion to the equatorial oxygen group. The second step is the release of sulfate facilitated by the spectator oxygen group [4]. By determining the energy profiles for both steps in this reaction I will determine which step is rate limiting and determine the route, associative or dissociative interchange, of the reaction. Model enzyme complexes have suggested that hydrogen donors in the active site play a key role in mediating this reaction. In previous studies performed we determined that the product release step is facilitated by pyridinium a hydrogen donor for the reaction. Pyridinium lowers the activation energy for the product release step (ΔH~ 30 kJ/mol) and promotes a dissociative interchange reaction route. In this study I will determine if hydrogen donors in the Mo active site behave as pyridinium does in the model enzyme complexes. Using Gaussian ONIOM to perform QM/MM calculations for the reaction of sulfite to sulfate catalyzed by SO, I will determine the energy profile of the reaction to identify the rate limiting step and the role of possible hydrogen donors in the active site of SO by comparing the reaction mechanism of two variants of SO with wild type SO. The variants will demonstrate the role as possible hydrogen bond donors of Tyrosine and water that are located in the active site of MO. The role of sulfite oxidase is crucial to the degradation of sulfite in the body and prevention of the accumulation of toxic sulfite in the body. Understanding how SO functions at a molecular level is crucial for the design and implementation of treatment for SO deficiency. The elementary steps of the enzyme activity can help determine specific roles of key residues in the enzyme. These steps cannot be seen in large scale enzyme kinetics studies, but computational studies allow the study of small movements and allow the study of these small‐scale reaction mechanics. Support or Funding Information Louis Stokes Alliance for Minority Participation (LSAMP) HRD # 1305011 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .