New insights into the biosynthesis of mycobacterial lipomannan arising from deletion of a conserved gene.
Genetic construction of a mutant strain (designated MSMEG4245) of Mycobacterium smegmatis, defective in a broadly conserved gene for a putative glycosyltransferase of the glycosyltransferase-C superfamily, results in a phenotype marked by the virtual absence of the phosphatidylinositol-containing lipomannan and lipoarabinomannan, replaced instead by a novel truncated form of lipomannan. The normal spectrum of phosphatidylinositol mannosides, long presumed precursors of these lipoglycans, was retained. Matrix-assisted laser desorption/ionization-time of flight/mass spectrometry of the mutated form of lipomannan shows a family of phosphatidylinositol-anchored lipomannans with from only 5 to 20 Manp residues as compared with lipomannan from the wild type strain consisting of 21-34 Manp residues but with few changes in the branching pattern. Thus, MSMEG4245 is apparently a key mannosyltransferase, required for the proper elongation of lipomannan to its normal state and subsequent synthesis of lipoarabinomannan. The corresponding ortholog in Mycobacterium tuberculosis H37Rv has been identified as Rv2174. This previously unrecognized feature of the biosynthesis of lipomannan/lipoarabinomannan allows a significant revision of structural and biosynthetic schemata and provides a molecular basis of selectivity in biosynthesis, as conferred by the MSMEG4245 gene.
Kaur
Devinder
D
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, 80523, the.
McNeil
Michael R
MR
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, 80523, the.
Khoo
Kay-Hooi
KH
Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan, and the.
Chatterjee
Delphi
D
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, 80523, the.
Crick
Dean C
DC
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, 80523, the.
Jackson
Mary
M
Unite de Genetique Mycobacterienne, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France.
Brennan
Patrick J
PJ
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, 80523, the. Electronic address: patrick.brennan@colostate.edu.
D000595:Amino Acid Sequence; D002874:Chromosome Mapping; D017353:Gene Deletion; D016680:Genome, Bacterial; D016695:Glycosyltransferases / Q000235:genetics*; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000235:genetics; D020102:Mycobacterium smegmatis / Q000235:genetics / Q000378:metabolism*
D008070:Lipopolysaccharides; C050016:lipoarabinomannan; C064351:lipomannan; D016695:Glycosyltransferases