title: The Proline/Glycine-Rich Region of the Biofilm Adhesion Protein Aap Forms an Extended Stalk that Resists Compaction.
abstract: Staphylococcus epidermidis is one of the primary bacterial species responsible for healthcare-associated infections. The most significant virulence factor for S. epidermidis is its ability to form a biofilm, which renders the bacteria highly resistant to host immune responses and antibiotic action. Intercellular adhesion within the biofilm is mediated by the accumulation-associated protein (Aap), a cell wall-anchored protein that self-assembles in a zinc-dependent manner. The C-terminal portion of Aap contains a 135-aa-long, proline/glycine-rich region (PGR) that has not yet been characterized. The region contains a set of 18 nearly identical AEPGKP repeats. Analysis of the PGR using biophysical techniques demonstrated the region is a highly extended, intrinsically disordered polypeptide with unusually high polyproline type II helix propensity. In contrast to many intrinsically disordered polypeptides, there was a minimal temperature dependence of the global conformational state of PGR in solution as measured by analytical ultracentrifugation and dynamic light scattering. Furthermore, PGR was resistant to conformational collapse or α-helix formation upon the addition of the osmolyte trimethylamine N-oxide or the cosolvent 2,2,2-trifluoroethanol. Collectively, these results suggest PGR functions as a resilient, extended stalk that projects the rest of Aap outward from the bacterial cell wall, promoting intercellular adhesion between cells in the biofilm. This work sheds light on regions of low complexity often found near the attachment point of bacterial cell wall-anchored proteins.
authors.affiliation: Graduate Program in Molecular Genetics, Biochemistry & Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA; Division of Immunobiology and Center for Systems Immunology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Yarawsky
authors.affiliation: Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA.
authors.forename: Lance R
authors.initials: LR
authors.lastname: English
authors.affiliation: Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Whitten
authors.affiliation: Division of Immunobiology and Center for Systems Immunology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA; Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA. Electronic address: andrew.herr@cchmc.org.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Herr
mesh_terms: D000595:Amino Acid Sequence; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D018441:Biofilms; D005998:Glycine / Q000737:chemistry*; D008744:Methylamines; D011392:Proline / Q000737:chemistry*; D013212:Staphylococcus epidermidis / Q000737:chemistry / Q000235:genetics; D014270:Trifluoroethanol; D037521:Virulence Factors / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D008744:Methylamines; D037521:Virulence Factors; D014270:Trifluoroethanol; D011392:Proline; C005855:trimethyloxamine; D005998:Glycine
keywords: Staphylococcus epidermidis; analytical ultracentrifugation; cell wall-anchored protein; circular dichroism; intrinsically disordered protein