X-ray crystallographic studies on Particulate Methane Monooxygenase, Thioredoxin A and Arginine Decarboxylase

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Title: X-ray crystallographic studies on Particulate Methane Monooxygenase, Thioredoxin A and Arginine Decarboxylase
Authors: Andrell, Juni
Item Type: Thesis or dissertation
Abstract: The work presented in this thesis describes the X-ray crystallographic studies of particulate methane monoxygenase (pMMO) from Methylococcus capsulatus (Bath), thioredoxin A (BsTrxA) from Bacillus subtilis and arginine decarboxylase (AdiA) from Escherichia coli. 1. pMMO is a respiratory enzyme that catalyses the first step in the metabolic pathway in methanotrophic bacteria by converting methane to methanol. The crystal structure of this integral membrane protein was determined by molecular replacement to 3.5 Å resolution. The three metal sites in pMMO were confirmed to be a mononuclear copper site, a dinuclear copper site and a mononuclear zinc site. 2. Thioredoxin is a ubiquitous protein present in nearly all known organisms. Its purpose in the cell is to maintain cysteine-containing proteins in the reduced state by converting intramolecular disulfide bonds to dithiols in a redox reaction. The crystal structure of an active site mutant of BsTrxA was determined by molecular replacement to 1.5 Å resolution. The structure shows a homodimer that resembles enzyme-substrate reaction intermediates. 3. AdiA is a vitamin B6-dependent enzyme that catalyses the decarboxylation of arginine into agmatine. It forms a part of an enzymatic system in E. coli that contribute to making this organism acid resistant. The structure of arginine decarboxylase (AdiA) from E. coli was determined by multiple isomorphous replacement and anomalous scattering (MIRAS) methods to 2.4 Å resolution. The structure revealed a ~800 kDa decamer composed as a pentamer of five homodimers. AdiA becomes active as the cellular environment becomes more acidic. The structure of AdiA suggests how functional decamers associate with decreasing pH or disassociates into inactive homodimers with increasing pH. The enzyme mechanism and determinants for substrate specificity are discussed within the framework of the structure and comparisons with related structures are made.
Issue Date: 2008
Date Awarded: Dec-2008
URI: http://hdl.handle.net/10044/1/4634
Supervisor: Carpenter, Liz
Iwata, So
Author: Andrell, Juni
Department: Molecular Biosciences
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Molecular Biosciences PhD theses



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