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Journal of Bacteriology, June 2001, p. 3680-3688, Vol. 183, No. 12
Department of Microbiology, University of
Georgia, Athens, Georgia 30602
Received 9 January 2001/Accepted 3 April 2001
Mycoplasma pneumoniae adsorbs to host respiratory
epithelium primarily by its attachment organelle, the proper function
of which depends upon mycoplasma adhesin and cytoskeletal proteins. Among the latter are the cytadherence-associated proteins HMW1 and
HMW2, whose specific roles in this process are unknown. In the M. pneumoniae cytadherence mutant I-2, loss of HMW2 results in
accelerated turnover of HMW1 and other cytadherence-accessory proteins,
probably by proteolysis. However, both the mechanism of degradation and
the means by which these proteins are rendered susceptible to it are
not understood. In this study, we addressed whether HMW1 degradation is
a function of its presence among specific subcellular fractions and
established that HMW1 is a peripheral membrane protein that is antibody
accessible on the outer surfaces of both wild-type and mutant I-2
M. pneumoniae but to a considerably lesser extent in the
mutant. Quantitation of HMW1 in Triton X-100-fractionated extracts from
cells pulse-labeled with [35S]methionine indicated that
HMW1 is synthesized in a Triton X-100-soluble form that exists in
equilibrium with an insoluble (cytoskeletal) form. Pulse-chase analysis
demonstrated that over time, HMW1 becomes stabilized in the
cytoskeletal fraction and associated with the cell surface in wild-type
M. pneumoniae. The less efficient transition to the
cytoskeleton and mycoplasma cell surface in mutant I-2 leads to
accelerated degradation of HMW1. These data suggest a role for HMW2 in
promoting export of HMW1 to the cell surface, where it is stable and
fully functional.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.12.3680-3688.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Stability of Mycoplasma pneumoniae
Cytadherence-Accessory Protein HMW1 Correlates with Its Association
with the Triton Shell

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Corresponding author. Mailing address: Department of
Microbiology, 523 Biological Sciences Bldg., University of Georgia,
Athens, GA 30602. Phone: (706) 542-2671. Fax: (706) 542-2674. E-mail: dkrause{at}arches.uga.edu.
Present address: Department of Veterinary Medicine, Kangwon
National University, Chuncheon, Korea.
Present address: The Scotts Company, Marysville, OH 43041.
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