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Journal of Bacteriology, December 2001, p. 7224-7230, Vol. 183, No. 24
Department of Microbiology, University of
Illinois, Urbana, Illinois 61801
Received 1 May 2001/Accepted 4 September 2001
An early step in the utilization of starch by Bacteroides
thetaiotaomicron is the binding of starch to the bacterial
surface. Four starch-associated outer membrane proteins of B. thetaiotaomicron that have no starch-degrading activity have been
identified. Two of these, SusC and SusD, have been shown by genetic
analysis to be required for starch binding. In this study, we provide
the first biochemical evidence that these two proteins interact
physically with each other. Both formaldehyde cross-linking and
nondenaturing gel electrophoresis experiments showed that SusC and SusD
interact to form a complex. Two other proteins encoded by genes in the same operon, SusE and SusF, proved not to be essential for starch utilization and actually decreased starch binding when they were present along with SusC and SusD. Consistent with this, nondenaturing gel analysis revealed that in a strain producing SusC, SusD, and SusE,
the SusCD complex was partially destabilized. The strain producing
SusC, SusD, and SusE also grew more slowly on starch than a strain
producing SusC, SusD, SusE, and SusF (µmax, 0.29 and
0.37/h, respectively). Thus, SusE appears to interact with the SusCD
complex. SusE also interacts with SusF, because SusE was less
susceptible to proteinase K digestion when SusF was present, and
nondenaturing gel analysis detected a complex formed by these two
proteins. Our results indicate that SusC, SusD, SusE, and SusF form a
protein complex in the outer membrane but that SusE and SusF are
dispensable members of this complex.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.24.7224-7230.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Biochemical Analysis of Interactions between Outer
Membrane Proteins That Contribute to Starch Utilization by
Bacteroides thetaiotaomicron
*
Corresponding author. Mailing address: Department of
Microbiology, 601 S. Goodwin Ave., CLSL 103, University of Illinois, Urbana, IL 61801. Phone: (217) 333-7378. Fax: (217) 244-8485. E-mail:
abigails{at}uiuc.edu.
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