title: Low expression level of glnA1 accounts for absence of cell wall associated poly-l-glutamate/glutamine in Mycobacterium smegmatis.
abstract: Cell wall associated poly-l-glutamine (PLG) layer synthesis is directly linked to glutamine synthetase (GS) encoded by glnA1 in tuberculosis causing mycobacteria. Avirulent Mycobacterium smegmatis (M. smegmatis) despite of having a glnA1 homolog lacks cell wall associated PLG layer. In the present study, we complemented a ΔglnA1 mutant of Mycobacterium bovis (lack PLG in cell wall) with M. smegmatis glnA1 cloned under M. bovis glnA1 promoter. PLG synthesis was restored in the cell wall of complemented strain. The complemented strain also showed increased resistance to physical stresses such as lysozyme, SDS and increased survival in THP-1 macrophages in comparison to the knockout. Further, in β-galactosidase reporter assay M. smegmatis glnA1 promoter showed ten times less activity as compared to M. bovis glnA1 promoter. GACT-8-11 → TGAC mutations in the M. smegmatis glnA1 promoter restored its activity by 60% as compared to the activity of glnA1 promoter of M. bovis. This mutation also showed increased GS expression and produced cell wall associated PLG in M. smegmatis. The results of this study demonstrate that glnA1 promoter of M. smegmatis accounts for low expression level of GS and apparently responsible for absence of cell wall associated PLG layer.
authors: Molecular Biology and Genetic Engineering Laboratory, School of Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: deeksha.jnu@gmail.com.
authors: Deeksha
authors: D
authors: Tripathi
authors: International Centre for Genetic Engineering and Biotechnology, New Delhi 110067, India. Electronic address: sashi.kant@osumc.edu.
authors: Sashi
authors: S
authors: Kant
authors: Molecular Biology and Genetic Engineering Laboratory, School of Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: rajni.garg@gmail.com.
authors: Rajni
authors: R
authors: Garg
authors: Molecular Biology and Genetic Engineering Laboratory, School of Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: rakeshbhatnagar@jnu.ac.in.
authors: Rakesh
authors: R
authors: Bhatnagar
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism*; D020102:Mycobacterium smegmatis / Q000378:metabolism*; D011099:Polyglutamic Acid / Q000378:metabolism*
chemical_list: D005973:Glutamine; D011099:Polyglutamic Acid; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase
keywords: Glutamine synthetase; Mycobacterium bovis; Mycobacterium smegmatis; Poly-l-glutamine/glutamate