Catalyzes the second step of the '4S' desulfurization pathway that removes covalently bound sulfur from dibenzothiophene (DBT) without breaking carbon-carbon bonds. Metabolizes DBT-sulfone (DBTO2 or DBT 5,5-dioxide) to an unidentified intermediate (not 2-hydroxybiphenyl (2-HBP)). DszA and DszB together metabolize DBTO2 to 2-HBP (PubMed:7961424, PubMed:7574582). Metabolizes DBTO2 to 2-(2'-hydroxyphenyl)benzene sulphinate (HBPS), also converts BPSo (biphenylenesultone (dibenz[c,e][l,2]oxathiin-6,6-dioxide)) to DHBP (2,2'-dihydroxybiphenyl) and sulfite (PubMed:9308179). The pathway substrate specificity has been augmented using mutagenesis, however no mutations allowed use of alkylated thiophenes (PubMed:11823208). Also acts on 3-methyl DBT sulfone (3-methyl dibenzothiophene 5,5-dioxide) yielding the 3-methylated derivative; mutating Gln-345 alters the product isomer ratio (PubMed:12967013). dibenzothiophene 5,5-dioxide + FMNH2 + NADH + O2 = 2'-hydroxybiphenyl-2-sulfinate + FMN + H(+) + H2O + NAD(+) Reduced flavin is provided by flavin reductase DszD. kcat is about 1 sec(-1). Sulfur metabolism; dibenzothiophene degradation. Homodimer. Expressed during growth on DBT or DMSO as sole sulfur source (at protein level) (PubMed:8932295). Part of the probable dszA-dszB-dszC operon (Probable). Desulfurization is repressed by sulfate, cysteine and methionine (PubMed:7574582, PubMed:8932295). DBTO2 but not 2-HBP is detected following growth on DBT. Can be used to remove sulfur from polycyclic aromatic sulfur compounds found in gasoline and diesel (biodesulfurization), which are a considerable source of pollution. In addition it may be possible to engineer the operon to make specialty chemicals. Belongs to the NtaA/SnaA/DszA monooxygenase family.