BACKGROUND: Cellobiose dehydrogenase (CDH) is a fungal extracellular oxidoreductase which fuels lytic polysaccharide monooxygenase with electrons during cellulose degradation. Interdomain electron transfer between the flavin and cytochrome domain in CDH, preceding the electron flow to lytic polysaccharide monooxygenase, is known to be pH dependent, but the exact mechanism of this regulation has not been experimentally proven so far. METHODS: To investigate the structural aspects underlying the domain interaction in CDH, hydrogen/deuterium exchange (HDX-MS) with improved proteolytic setup (combination of nepenthesin-1 with rhizopuspepsin), native mass spectrometry with ion mobility and electrostatics calculations were used. RESULTS: HDX-MS revealed pH-dependent changes in solvent accessibility and hydrogen bonding at the interdomain interface. Electrostatics calculations identified these differences to result from charge neutralization by protonation and together with ion mobility pointed at higher electrostatic repulsion between CDH domains at neutral pH. In addition, we uncovered extensive O-glycosylation in the linker region and identified the long-unknown exact cleavage point in papain-mediated domain separation. CONCLUSIONS: Transition of CDH between its inactive (open) and interdomain electron transfer-capable (closed) state is shown to be governed by changes in the protein surface electrostatics at the domain interface. Our study confirms that the interdomain electrostatic repulsion is the key factor modulating the functioning of CDH. GENERAL SIGNIFICANCE: The results presented in this paper provide experimental evidence for the role of charge repulsion in the interdomain electron transfer in cellobiose dehydrogenases, which is relevant for exploiting their biotechnological potential in biosensors and biofuel cells.

BioCeV Institute of Microbiology The Czech Academy of Sciences Prumyslova 595 252 50 Vestec Czech Republic

BioOrganic Mass Spectrometry Laboratory IPHC Université de Strasbourg 25 rue Becquerel 67087 Strasbourg France

Department of Biochemistry Faculty of Science Charles University Prague Hlavova 8 128 43 Prague Czech Republic

Department of Food Sciences and Technology BOKU University of Natural Resources and Life Sciences Muthgasse 18 1190 Vienna Austria

IPHC CNRS UMR7178 67087 Strasbourg France

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$a Kadek, Alan $u BioCeV - Institute of Microbiology, The Czech Academy of Sciences, Prumyslova 595, 252 50 Vestec, Czech Republic; Department of Biochemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Prague, Czech Republic.

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$a Interdomain electron transfer in cellobiose dehydrogenase is governed by surface electrostatics / $c A. Kadek, D. Kavan, J. Marcoux, J. Stojko, AK. Felice, S. Cianférani, R. Ludwig, P. Halada, P. Man,

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$a BACKGROUND: Cellobiose dehydrogenase (CDH) is a fungal extracellular oxidoreductase which fuels lytic polysaccharide monooxygenase with electrons during cellulose degradation. Interdomain electron transfer between the flavin and cytochrome domain in CDH, preceding the electron flow to lytic polysaccharide monooxygenase, is known to be pH dependent, but the exact mechanism of this regulation has not been experimentally proven so far. METHODS: To investigate the structural aspects underlying the domain interaction in CDH, hydrogen/deuterium exchange (HDX-MS) with improved proteolytic setup (combination of nepenthesin-1 with rhizopuspepsin), native mass spectrometry with ion mobility and electrostatics calculations were used. RESULTS: HDX-MS revealed pH-dependent changes in solvent accessibility and hydrogen bonding at the interdomain interface. Electrostatics calculations identified these differences to result from charge neutralization by protonation and together with ion mobility pointed at higher electrostatic repulsion between CDH domains at neutral pH. In addition, we uncovered extensive O-glycosylation in the linker region and identified the long-unknown exact cleavage point in papain-mediated domain separation. CONCLUSIONS: Transition of CDH between its inactive (open) and interdomain electron transfer-capable (closed) state is shown to be governed by changes in the protein surface electrostatics at the domain interface. Our study confirms that the interdomain electrostatic repulsion is the key factor modulating the functioning of CDH. GENERAL SIGNIFICANCE: The results presented in this paper provide experimental evidence for the role of charge repulsion in the interdomain electron transfer in cellobiose dehydrogenases, which is relevant for exploiting their biotechnological potential in biosensors and biofuel cells.

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$a Kavan, Daniel $u BioCeV - Institute of Microbiology, The Czech Academy of Sciences, Prumyslova 595, 252 50 Vestec, Czech Republic; Department of Biochemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Prague, Czech Republic.

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$a Marcoux, Julien $u BioOrganic Mass Spectrometry Laboratory (LSMBO), IPHC, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France; IPHC, CNRS, UMR7178, 67087 Strasbourg, France.

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$a Stojko, Johann $u BioOrganic Mass Spectrometry Laboratory (LSMBO), IPHC, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France; IPHC, CNRS, UMR7178, 67087 Strasbourg, France.

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$a Felice, Alfons K G $u Department of Food Sciences and Technology, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, 1190 Vienna, Austria.

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$a Cianférani, Sarah $u BioOrganic Mass Spectrometry Laboratory (LSMBO), IPHC, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France; IPHC, CNRS, UMR7178, 67087 Strasbourg, France.

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$a Ludwig, Roland $u Department of Food Sciences and Technology, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, 1190 Vienna, Austria.

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$a Halada, Petr $u BioCeV - Institute of Microbiology, The Czech Academy of Sciences, Prumyslova 595, 252 50 Vestec, Czech Republic.

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$a Man, Petr $u BioCeV - Institute of Microbiology, The Czech Academy of Sciences, Prumyslova 595, 252 50 Vestec, Czech Republic; Department of Biochemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Prague, Czech Republic. Electronic address: pman@biomed.cas.cz.

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