Dissertation

Conserved Variation in Tandem Repeat Sequences Tunes the Self-Assembly and Stability Characteristics of the Staphylococcus epidermidis Biofilm Protein Aap

Shelton, Catherine L

2016

Overview

Staphylcoccus epidermidis is a ubiquitous commensal of the human skin with few virulence factors; however once inside the body it can form robust biofilms, that are virtually resistant to antibiotic treatment, on indwelling medical devices. Accumulation associated protein (Aap) is a S. epidermidis cell-wall associated protein (CWA) that plays an important role in mediating cell-cell adhesion within the biofilm. Specifically, the B-repeat regions –comprised of extended, ribbon-like ß-sheet modules –overlap from two adjacent cells and form a zinc-zipper with two zinc ions coordinated between each set of anti-parallel B-repeats. This work describes important new findings that refine our understanding of Aap-mediated accumulation of bacterial cells. Though highly identical, Aap B-repeat sequences contain a region of conserved variant amino acids in some of the repeats, but not in others. Interestingly, the alternative set of residues is clustered at the most critical region of the protein –the dimerization interface. Biophysical and structural characterization of repeats containing the conserved variant amino acids shows that these changes at the dimerization interface alter binding affinity and assembly of B-repeats. As a result, the previous model of zinc-zipper adhesion with equal affinity at each dimer interface has been modified to account for a mixture of both high- and low-affinity dimer interfaces along the length of the B-repeat region. These findings not only clarify our understanding of Aap-mediated cell accumulation, but also provide critical information for the development of novel antibody and vaccine targets.

• Publisher: ProQuest Dissertations & Theses
• Subject: Biochemistry
• ISBN: 9780438390942, 0438390946