3 research outputs found
Correction for Kipkorir et al., "De Novo Cobalamin Biosynthesis, Transport, and Assimilation and Cobalamin-Mediated Regulation of Methionine Biosynthesis in Mycobacterium smegmatis"
Volume 203, no. 7, e00620-20, 2021, https://doi.org/10.1128/JB.00620-20. Page 1: This article was published on 8 March 2021 with Stephanie S. Dawes missing from the byline. The byline was updated in the version posted on 21 January 2022. The following corrections were also made in that version. Page 1, footnote box: The following footnote was added. “§Present address: Stephanie S. Dawes, Laboratory of Structural Biology, School of Biological Sciences and Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand.” Page 14, Acknowledgments, line 3: “and Stephanie Dawes for providing the DmetE cobK::hyg mutant” was deleted. Page 14, Acknowledgments, lines 1 and 2 from bottom: “(to V.M. and D.F.W.)” was changed to “(to S.S.D., V.M., and D.F.W.).
Substrate specificity of an oxygen dependent sulfoxide synthase in ovothiol biosynthesis
OvoA is an iron(II) dependent sulfoxide synthase which catalyzes the first step in ovothiol A biosynthesis. This enzyme sulphurizes the Câ‚… position of the imidazole side chain of L-histidine. We report the substrate specificity profile of this catalyst and present data which indicate that OvoA catalysis follows an thiol-ene type mechanism
De Novo Cobalamin Biosynthesis, Transport, and Assimilation and Cobalamin-Mediated Regulation of Methionine Biosynthesis in Mycobacterium smegmatis.
Cobalamin is an essential cofactor in all domains of life, yet its biosynthesis is restricted to some bacteria and archaea. Mycobacterium smegmatis, an environmental saprophyte frequently used as surrogate for the obligate human pathogen M. tuberculosis, carries approximately 30 genes predicted to be involved in de novo cobalamin biosynthesis. M. smegmatis also encodes multiple cobalamin-dependent enzymes, including MetH, a methionine synthase that catalyzes the final reaction in methionine biosynthesis. In addition to metH, M. smegmatis possesses a cobalamin-independent methionine synthase, metE, suggesting that enzyme use-MetH versus MetE-is regulated by cobalamin availability. Consistent with this notion, we previously described a cobalamin-sensing riboswitch controlling metE expression in M. tuberculosis Here, we apply a targeted mass spectrometry-based approach to confirm de novo cobalamin biosynthesis in M. smegmatis during aerobic growth in vitro We also demonstrate that M. smegmatis can transport and assimilate exogenous cyanocobalamin (CNCbl; also known as vitamin B12) and its precursor, dicyanocobinamide ([CN]2Cbi). However, the uptake of CNCbl and (CN)2Cbi in this organism is restricted and seems dependent on the conditional essentiality of the cobalamin-dependent methionine synthase. Using gene and protein expression analyses combined with single-cell growth kinetics and live-cell time-lapse microscopy, we show that transcription and translation of metE are strongly attenuated by endogenous cobalamin. These results support the inference that metH essentiality in M. smegmatis results from riboswitch-mediated repression of MetE expression. Moreover, differences observed in cobalamin-dependent metabolism between M. smegmatis and M. tuberculosis provide some insight into the selective pressures which might have shaped mycobacterial metabolism for pathogenicity.IMPORTANCE Alterations in cobalamin-dependent metabolism have marked the evolution of Mycobacterium tuberculosis into a human pathogen. However, the role(s) of cobalamin in mycobacterial physiology remains poorly understood. Using the nonpathogenic saprophyte M. smegmatis, we investigated the production of cobalamin, transport and assimilation of cobalamin precursors, and the role of cobalamin in regulating methionine biosynthesis. We confirm constitutive de novo cobalamin biosynthesis in M. smegmatis, in contrast with M. tuberculosis, which appears to lack de novo cobalamin biosynthetic capacity. We also show that uptake of cyanocobalamin (vitamin B12) and its precursors is restricted in M. smegmatis, apparently depending on the cofactor requirements of the cobalamin-dependent methionine synthase. These observations establish M. smegmatis as an informative foil to elucidate key metabolic adaptations enabling mycobacterial pathogenicity