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Infection and Immunity, August 1999, p. 3952-3959, Vol. 67, No. 8
Department of Microbiology and Immunology,
University of Arkansas for Medical Sciences, Little Rock, Arkansas
722051; Department of Chemical and
Biochemical Engineering, University of Maryland
Received 7 January 1999/Returned for modification 12 April
1999/Accepted 30 April 1999
The Staphylococcus aureus collagen adhesin (CNA) occurs
in at least four forms that differ in the number (one, two, three, or
four) of B domains. The B domains contain 187 amino acids and are
located between the domains that anchor CNA to the cell envelope and
the ligand-binding A domain. To determine whether a B domain is
required for functional expression of CNA, we cloned the 2B cna gene from S. aureus strain Phillips and
then eliminated both B domains by overlapping PCR. The absence of a B
domain did not affect processing of the collagen adhesin to the cell
surface or the ability to bind collagen. Based on our recent
demonstration that the capsule can mask CNA on the surface of S. aureus cells (A. F. Gillaspy et al., Infect. Immun.
66:3170-3178, 1998), we also investigated the possibility that
multiple B domains can extend the ligand-binding A domain outward from
the cell surface and thereby overcome the inhibitory effect of the
capsule. Specifically, we cloned the naturally occurring 4B CNA variant
from S. aureus UAMS-639 and, by successive elimination of B
domains, generated 1, 2, and 3B variants that are isogenic with respect
to the 4B clone. After introducing each variant into microencapsulated
and heavily encapsulated strains of S. aureus and growing
cells under conditions known to affect capsule production (e.g., growth
on Columbia agar), we correlated capsule production with exposure of
CNA on the cell surface and the ability to bind collagen. Under no
circumstance was the masking effect of the capsule reduced by the
presence of multiple B domains. These results indicate that the B
domains do not extend the ligand-binding A domain outward in a fashion
that can overcome the inhibition of collagen binding associated with
capsule production.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Functional Analysis of the Staphylococcus
aureus Collagen Adhesin B Domain
Baltimore County,
Baltimore, Maryland 212502; and
University of Kansas Medical Center, Kansas City, Kansas
661603
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Slot 511, University of Arkansas for
Medical Sciences, 4301 W. Markham, Little Rock, AR 72205. Phone: (501) 686-7958. Fax: (501) 686-5359. E-mail:
smeltzermarks{at}exchange.uams.edu.
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