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Title: Discovery of novel lignin oxidizing enzymes from Sphingobacterium sp.T2
Author: Rashid, Goran M. M.
ISNI:       0000 0004 5915 9104
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2015
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Bacterial lignin-degrading strain Sphingobacterium sp. T2 is reported as most active strain among 12 isolates and proteomic analysis of extracellular fractions gave hits for two superoxide dismutase enzymes. Two novel lignin-oxidising enzymes from Sphingobacterium sp. T2 were identified. Experimental and bioinformatic evidence revealed that these enzymes are extracellular superoxide dismutases, namely SOD1 and SOD2. Both enzyme genes have been cloned and overexpressed in Escherichia coli. The metal specificity of both enzymes was investigated using ICP-OES, UV-vis spectra and superoxide dismutation activity of different metal-containing enzyme preparations, the results indicate that both enzymes (SOD1 and SOD2) are manganese-containing SOD. MnSOD1 and MnSOD2 from Sphingobacterium sp. T2 (SpMnSODs) exhibit time-dependent lignin-oxidising ability, they can depolymerise wheat straw organosolv lignin, modify Kraft lignin, and lignocellulose materials (pine and miscanthus). Analysis of reaction components of SpMnSOD enzymes with organosolv lignin by HPLC, LC/MS and GC/MS show that SOD1 and SOD2 generate 10 new products. These metabolites were identified by comparison of their retention times and mass fragmentation pattern produced by LC/MS and GC/MS with their authentic analogue. The mechanism of reaction and reactive species generated by SpMnSODs were elucidated from their identified reaction products. Results indicate that SpMnSOD enzymes produce highly reactive species (hydroxyl radical) and catalyse several types of reactions which include: Ca-Cß cleavage, arylC-Ca Cleavage, -OCH3 group replacement with -OH group, hydroxylation of aromatic rings, Ipso-substitution and decarboxylation. The X-ray crystal structure of MnSOD1 was determined to 1.35 Å resolution, showing that MnSOD1 has a typical homodimer with a Mn(II) ion in each active site ligated by three His, one Asp, and a water/hydroxide forming trigonal bipyramidal geometry. The reaction of SpMnSOD enzymes with lignin model compounds confirms that these enzymes can catalyse Ca-Cß cleavage, arylC-Ca Cleavage, ipso-substitution, decarboxylation, demethoxylation, hydroxylation of aromatic rings and fragmentation of propenoic acid side chains which in turn are evidence of generation of highly oxidising species (hydroxyl radical).
Supervisor: Not available Sponsor: Ministry of Higher Education and Scientific Research (Kurdistan)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry ; QK Botany