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Infect. Immun. doi:10.1128/IAI.01288-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of LpxL, a late Acyl Transferase of Francisella tularensis

Department of Microbiology, University of Iowa, Iowa City, Iowa, The Buck Institute for Age Research, Novato, CA, Department of Pharmaceutical Chemistry, The University of California, San Francisco, CA

^* To whom correspondence should be addressed. Email: bgibson{at}buckinstitute.org.

	Abstract

Lipopolysaccharide (LPS) is a major component of the outer membrane of gram-negative bacteria, and the lipid A region of LPS mediates stimulation of the immune system in a structure dependent manner. Unlike the LPS of many other gram-negative bacteria, the LPS of F. tularensis isolated from in vitro cultures is not proinflammatory. This observed lack of proinflammatory prowess may reflect structural features of the lipid A, such as the number and length of the acyl chains and the single phosphate group. To better understand this phenotype, we have begun to elucidate LPS biosynthesis in F. tularensis. We present complementation, mutational, and chemical data demonstrating that F. tularensis FTT0232c encodes a functional late acyltransferase enzyme, with specificity similar to the E. coli LpxL ortholog. Expression of this late acyltransferase complemented the temperature-sensitive and hypoacylated lipid A phenotypes of an E. coli lpxL mutant, expression of FTT0232c is increased during intracellular growth relative to in vitro growth, and finally, LPS obtained from a mutant of F. tularensis lacking FTT0232c showed an abundant triacyl lipid A species after mass spectrometric analysis consistent with loss of an LpxL late acyl transferase.