Transfer of the first arabinofuranose residue to galactan is essential for Mycobacterium smegmatis viability.
The mycobacterial arabinan is an elaborate component of the cell wall with multiple glycosyl linkages and no repeating units. In Mycobacterium spp., the Emb proteins (EmbA, EmbB, and EmbC) have been identified as putative mycobacterial arabinosyltransferases implicated in the biogenesis of the cell wall arabinan. Furthermore, it is now evident that the EmbA and EmbB proteins are involved in the assembly of the nonreducing terminal motif of arabinogalactan and EmbC is involved in transferring arabinose, perhaps in the early stage of arabinan synthesis in lipoarabinomannan. It has also been shown that the Emb proteins are a target of the antimycobacterial drug ethambutol (EMB). In the search for additional mycobacterial arabinosyltransferases in addition to the Emb proteins, we disrupted MSMEG_6386 (an orthologue of Rv3792 and a gene upstream of embC) in Mycobacterium smegmatis. Allelic exchange at the chromosomal MSMEG_6386 locus of M. smegmatis could only be achieved in the presence of a rescue plasmid carrying a functional copy of MSMEG_6386 or Rv3792, strongly suggesting that MSMEG_6386 is essential. An in vitro arabinosyltransferase assay using a membrane preparation from M. smegmatis expressing Rv3792 and synthetic beta-d-Galf-(1-->5)-beta-D-Galf-(1-->6)-beta-D-Galf-octyl and beta-D-Galf-(1-->6)-beta-D-Galf-(1-->5)-beta-D-Galf-octyl showed that Rv3792 gene product can transfer an arabinose residue to the C-5 position of the internal 6-linked galactose. The reactions were insensitive to EMB, and when alpha-d-Manp-(1-->6)-alpha-D-Manp-(1-->6)-alpha-D-Manp-octylthiomethyl was used as an acceptor, no product was formed. These observations indicate that transfer of the first arabinofuranose residue to galactan is essential for M. smegmatis viability.
Shi
Libin
L
Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado 80523-1682, USA.
Zhou
Roukun
R
Liu
Zhentong
Z
Lowary
Todd L
TL
Seeberger
Peter H
PH
Stocker
Bridget L
BL
Crick
Dean C
DC
Khoo
Kay-Hooi
KH
Chatterjee
Delphi
D
D001089:Arabinose / Q000031:analogs & derivatives* / Q000378:metabolism; D002240:Carbohydrate Sequence; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004977:Ethambutol / Q000494:pharmacology; D005685:Galactans / Q000378:metabolism*; D017353:Gene Deletion; D005798:Genes, Bacterial; D020043:Genes, Essential; D050296:Microbial Viability; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D020102:Mycobacterium smegmatis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D010430:Pentosyltransferases / Q000235:genetics / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D004791:Enzyme Inhibitors; D005685:Galactans; C431714:arabinofuranose; D004977:Ethambutol; D001089:Arabinose; D010430:Pentosyltransferases; C101967:arabinosyltransferase