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Journal of Bacteriology, December 1999, p. 7285-7290, Vol. 181, No. 23
Department of Bacteriology, University of
Wisconsin-Madison, Madison, Wisconsin 53706
Received 6 July 1999/Accepted 16 September 1999
ApbE is a lipoprotein in Salmonella typhimurium, and
mutants unable to make this protein have a reduced ability to make
thiamine (vitamin B1) and require it as a supplement for
optimal growth in minimal glucose medium. Polyclonal antibodies
specific to ApbE were used to determine that wild-type ApbE is located
exclusively in the inner membrane. The periplasmic, monotopic topology
of ApbE was determined by using computer-based hydrophobicity plots, LacZ and PhoA gene fusions, and proteinase protection experiments. This
extracellular location of ApbE is required for its function, since a
cytoplasmic form (ApbEcyto) did not allow an
apbE mutant to grow in the absence of thiamine. A
periplasmic form of ApbE (ApbEperi) lacking the lipoprotein
modification allowed an apbE mutant to grow in the absence
of thiamine, indicating that soluble ApbE could function in thiamine
synthesis and that lipoation and membrane association were not
required. Alteration of the amino acid implicated in membrane sorting
for other lipoproteins did not result in a relocalization of ApbE to
the outer membrane, suggesting that additional sorting determinants
exist for ApbE.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
A Periplasmic Location Is Essential for the Role of
the ApbE Lipoprotein in Thiamine Synthesis in Salmonella
typhimurium
*
Corresponding author. Mailing address: University of
Wisconsin-Madison, Department of Bacteriology, 1550 Linden Dr.,
Madison, WI 53706. Phone: (608) 265-4630. Fax: (608) 262-9865. E-mail: downs{at}bact.wisc.edu.
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