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Infection and Immunity, April 2001, p. 2180-2189, Vol. 69, No. 4
Department of Microbiology and Immunology, F. Edward Hébert School of Medicine, Uniformed Services
University of the Health Sciences, Bethesda, Maryland 20814
Received 11 August 2000/Returned for modification 7 November
2000/Accepted 22 December 2000
The Mxi-Spa type III secretion system of Shigella
flexneri directs the host cell contact-induced secretion of a set
of invasins, referred to as Ipas. In this study, we examined the role
of Spa33 in Ipa secretion. A spa33-null mutant was both
noninvasive and unable to translocate the Ipas from inner membrane to
outer membrane (OM) positions of the Mxi-Spa transmembrane channel.
Spa33 was found to be a Mxi-Spa substrate that is translocated to the
bacterial cell surface upon the induction of Ipa secretion. This
mobility may serve to drive Ipa translocation within Mxi-Spa toward OM positions. Consistent with a second distinct role in regulating Ipa
traffic, the overexpression of Spa33 also blocked Ipa secretion and
resulted in Ipa accumulation at the OM. Co-overexpression of Spa33 and
another OM-associated element, Spa32, did not disrupt Ipa secretion,
suggesting an interaction between the two proteins and an effect on the
mechanism which serves to regulate Ipa release from the OM. These
findings indicate that Spa33 is a mobile element within Mxi-Spa, which
is required to control Ipa translocation into and out of OM positions
of the secretory structure.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.4.2180-2189.2001
Spa33, a Cell Surface-Associated Subunit of the
Mxi-Spa Type III Secretory Pathway of Shigella
flexneri, Regulates Ipa Protein Traffic
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, F. Edward Hébert School of Medicine,
Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799. Phone: (301) 295-3415. Fax: (301) 295-1545. E-mail: amaurelli{at}usuhs.mil.
Infection and Immunity, April 2001, p. 2180-2189, Vol. 69, No. 4
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.4.2180-2189.2001
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