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J Bacteriol, February 1998, p. 505-513, Vol. 180, No. 3
Department of Microbiology and
Immunology,1
Division of Infectious
Diseases,
Received 3 September 1997/Accepted 4 December 1997
One of the most abundant proteins synthesized by Legionella
pneumophila, particularly during growth in a variety of
eukaryotic host cells, is Hsp60, a member of the GroEL family of
molecular chaperones. The present study was initiated in response to a
growing number of reports suggesting that for some bacteria, including L. pneumophila, Hsp60 may exist in extracytoplasmic
locations. Immunolocalization techniques with Hsp60-specific monoclonal
and polyclonal antibodies were used to define the subcellular location and distribution of Hsp60 in L. pneumophila grown in vitro,
or in vivo inside of HeLa cells. For comparative purposes
Escherichia coli, expressing recombinant L. pneumophila Hsp60, was employed. In contrast to E. coli, where Hsp60 was localized exclusively in the cytoplasm, in
L. pneumophila Hsp60 was predominantly associated with the
cell envelope, conforming to a distribution pattern typical of surface
molecules that included the major outer membrane protein OmpS and
lipopolysaccharide. Interestingly, heat-shocked L. pneumophila organisms exhibited decreased overall levels of
cell-associated Hsp60 epitopes and increased relative levels of surface
epitopes, suggesting that Hsp60 was released by stressed bacteria.
Putative secretion of Hsp60 by L. pneumophila was further
indicated by the accumulation of Hsp60 in the endosomal space, between
replicating intracellular bacteria. These results are consistent with
an extracytoplasmic location for Hsp60 in L. pneumophila
and further suggest both the existence of a novel secretion mechanism
(not present in E. coli) and a potential role in
pathogenesis.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Immunolocalization of Hsp60 in
Legionella pneumophila
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Faculty of Medicine, Sir Charles Tupper Medical Bldg., Dalhousie University, Halifax, Nova Scotia, Canada B3H
4H7. Phone: (902) 494-3889. Fax: (902) 494-5125. E-mail:
hoffmanp{at}tupdean1.med.dal.ca.
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