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Structural studies on the extracellular flavocytochrome cellobiose dehydrogenase from Phanerochaete chrysosporium
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microorganisms that degrade lignocellulose play an important role in maintaining the global carbon cycle. Under cellulolytic conditions, the fungus Phanerochaete chrysosporium produces an extracellular flavocytochrome, cellobiose dehydrogenase (CDH), with a proposed role in lignocellulose degradation. CDH consists of 755 amino acids including a C-terminal flavodehydrogenase linked by a peptide hinge to an N-terminal b-type cytochrome. The enzyme catalyses the oxidation of cellobiose to cellobiono-1,5-lactone, followed by transfer of electrons to an electron acceptor, either directly by the flavodehydrogenase domain, or via the cytochrome domain. This thesis presents a structural study on the individual domains of P. chrysosporium cellobiose dehydrogenase.

The crystal structure of the cytochrome was determined at 1.9 Å resolution. It folds as a β-sandwich with the topology of the antibody Fab V(H) domain, and the haem iron is ligated by Met65 and His163. This is only the second example of a b-type cytochrome with this ligation. The haem propionates are surface exposed to facilitate interdomain electron transfer.

The structure of a cytochrome Met65His mutant was determined at 1.9 Å resolution. In the mutant, the iron is ligated by the histidyl δ and ε nitrogens, rather than the usual N-ε/N-εligation. This is the first example of a bis-His N-ε/N-δ coordinated protoporphyrin IX iron. The structure of the flavoprotein domain was determined at 1.5 Å resolution. It is partitioned into an FAD-binding subdomain of α/β-type and a substrate-binding subdomain consisting of a seven-stranded β-sheet and six α-helices. Furthermore, the structure of the flavoprotein with the inhibitor cellobiono-1,5-lactam at 1.8 Å resolution lends support to a hydride-transfer mechanism for the reductive-half reaction of CDH although a radical mechanism cannot be excluded.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 48
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 767
Keyword [en]
Cell and molecular biology, cellobiose dehydrogenase, flavocytochrome, hydride transfer, radical mechanism, X-ray crystallography
Keyword [sv]
Cell- och molekylärbiologi
National Category
Biochemistry and Molecular Biology
Research subject
Biology, with specialization in structural biology
Identifiers
URN: urn:nbn:se:uu:diva-2701ISBN: 91-554-5448-8 (print)OAI: oai:DiVA.org:uu-2701DiVA, id: diva2:162075
Public defence
2002-11-22, B42, Biomedical Centre, Uppsala, 13:15
Opponent
Available from: 2002-10-30 Created: 2002-10-30Bibliographically approved

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