title: Inactivation of the regulatory protein B of soluble methane monooxygenase from Methylococcus capsulatus (Bath) by proteolysis can be overcome by a Gly to Gln modification.
abstract: The regulatory protein B of soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath), exists as a mixture of the full-length active form and truncated forms, B' and B". Electrospray ionisation mass spectrometry (ESI-MS) was used to identify a cleavage site between Met12 and Gly13, such that 12 amino acids were lost from the N-terminus of protein B. This truncate was designated B' and molecular masses were assigned to proteins B and B' of 15,852.6+/-0.4 Da and 14,629.5+/-0.3 Da, respectively. A cleavage site between Gln29 and Val30 was also identified such that 29 amino acids were lost from the N-terminus of protein B. This truncate was designated B" and had a molecular mass of 12,709.93+/-0.02 Da. Proteins B' and B" were found to be inactive in the sMMO system. Addition of protease inhibitors or the heterologous expression of protein B in various strains of lon-deficient or ompT-deficient Escherichia coli, did not inhibit B' formation. Expression of protein B as a glutathione S-transferase fusion protein and subsequent purification of protein B from E. coli using affinity chromatography resulted in preparations of protein B with higher enzyme activities than that of wild-type protein B. However, ESI-MS confirmed that protein B' was still present. Alteration of the Met12-Gly13 cleavage site to Met12-Gln13 revealed that the stability of G13Q at 20 degrees C and 37 degrees C was higher than that of wild-type preparations. ESI-MS indicated that protein B' was absent and could only be identified after prolonged incubation at room temperature. The amount of active protein B present in the cell may be controlled by protein B cleavage, thereby regulating electron transfer. Alternatively, it may allow protein B to maintain a certain conformation necessary for enzyme activity and this may control the activity of sMMO in response to the supply of methane to the cell.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry, United Kingdom.
authors.forename: J S
authors.initials: JS
authors.lastname: Lloyd
authors.forename: A
authors.initials: A
authors.lastname: Bhambra
authors.forename: J C
authors.initials: JC
authors.lastname: Murrell
authors.forename: H
authors.initials: H
authors.lastname: Dalton
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D005973:Glutamine / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D046911:Macromolecular Substances; D013058:Mass Spectrometry; D008772:Methylococcaceae / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010105:Oxygenases / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics; D012995:Solubility
chemical_list: D017931:DNA Primers; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D005973:Glutamine; D010105:Oxygenases; C021555:methane monooxygenase; D005998:Glycine