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Infection and Immunity, November 1998, p. 5202-5207, Vol. 66, No. 11
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
The Major Outer Membrane Protein of Chlamydia
psittaci Functions as a Porin-Like Ion Channel
Susan
Wyllie,1,2
Richard H.
Ashley,2
David
Longbottom,1,* and
Alan J.
Herring1,
Moredun Research Institute, International
Research Centre, Pentland Science Park, Penicuik, Midlothian EH26
0PZ,1 and
Department of Biochemistry,
University of Edinburgh, Edinburgh EH8 9XD,2
United Kingdom
Received 17 April 1998/Returned for modification 4 June
1998/Accepted 20 August 1998
The major outer membrane protein (MOMP) of Chlamydia
species shares several biochemical properties with classical porin
proteins. Secondary structure analysis by circular dichroism now
reveals that MOMP purified from Chlamydia psittaci has a
predominantly
-sheet content (62%), which is also typical of
bacterial porins. Can MOMP form functional ion channels? To directly
test the "porin channel" hypothesis at the molecular level, the
MOMP was reconstituted into planar lipid bilayers, where it gave rise
to multibarreled channels, probably trimers, which were modified by an
anti-MOMP monoclonal antibody. These observations are consistent with
the well-characterized homo-oligomeric nature of MOMP previously
revealed by biochemical analysis and with the triple-barreled behavior of other porins. MOMP channels were weakly anion selective
(PCl/PK ~ 2) and
permeable to ATP. They may therefore be a route by which Chlamydia can take advantage of host nucleoside
triphosphates and explain why some anti-MOMP antibodies neutralize
infection. These findings have broad implications on the search for an
effective chlamydial vaccine to control the significant human and
animal diseases caused by these organisms.
*
Corresponding author. Mailing address: Moredun Research
Institute, International Research Centre, Pentland Science Park,
Penicuik, Midlothian EH26 0PZ, United Kingdom. Phone: 44 (0)131 445 6136. Fax: 44 (0)131 445 6235. E-mail:
longd{at}mri.sari.ac.uk.
Present address: The Public Health Laboratory, Kingsdown, Bristol
BS2 8EL, United Kingdom.
Infection and Immunity, November 1998, p. 5202-5207, Vol. 66, No. 11
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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