Functional consequences of B-repeat sequence variation in the staphylococcal biofilm protein Aap: deciphering the
Catherine L Shelton1,2, Deborah G Conrady2, Andrew B Herr2,3
1Program in Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, U.S.A.
The Biochemical Journal
|November 23, 2016
Summary
Staphylococcus epidermidis biofilm formation relies on the accumulation-associated protein (Aap). Its B-repeat subtypes influence zinc-mediated dimerization and stability, impacting bacterial adhesion.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Staphylococcus epidermidis forms robust biofilms, contributing to antibiotic resistance.
- Biofilm intercellular adhesion is mediated by the accumulation-associated protein (Aap).
- Aap's B-repeat region mediates zinc-dependent self-assembly, crucial for adhesion.
Purpose of the Study:
- To investigate the functional significance of Aap B-repeat subtypes in Staphylococcus epidermidis.
- To elucidate the structural and mechanistic basis for differential B-repeat function.
Main Methods:
- Analytical ultracentrifugation to assess protein dimerization.
- Circular dichroism thermal denaturation to determine protein stability.
- X-ray crystallography to determine protein structures.
Main Results:
- Variant B-repeat sequences exhibited reduced or absent Zn2+-induced dimerization.
- Variant sequences significantly stabilized the B-repeat fold, depending on location.
- Crystal structures revealed stabilizing bonding networks and altered electrostatic potentials at the Zn2+-binding site.
Conclusions:
- Distinct Aap B-repeat subtypes possess unique functional properties influencing dimerization and stability.
- An 'assembly code' governs Aap B-repeat oligomerization, crucial for biofilm formation.
- A 'slip-grip' model explains initial contact and firm adhesion during Staphylococcus epidermidis biofilm development.
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