bi0c00625_si_001.pdf (2.05 MB)
Spectroscopic Identification of Peptide Chemistry in the Caulobacter crescentus Holdfast
journal contribution
posted on 2020-09-05, 14:29 authored by Alex Nyarko, Saranshu Singla, Hazel A. Barton, Ali DhinojwalaThe
bacterium Caulobacter crescentus is known
to attach irreversibly to underwater surfaces by utilizing an adhesive
structure called the holdfast, which exhibits the greatest known adhesive
strength of any organism. The very small size of the holdfast (∼400
nm wide and ∼40 nm high) has made direct chemical analysis
difficult, and its structure remains poorly understood. In this study,
we employ spectroscopic techniques, including attenuated total reflection
infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy,
to probe holdfast chemistry. The data indicate the presence of a peptide
signal within the holdfast polymer. By comparing the ATR-IR spectrum
of the holdfast to peptidoglycan spectra from other bacterial species,
we demonstrate the similarity of the holdfast chemistry to that of
peptidoglycan, suggesting peptide cross-linking may play a role in
holdfast architecture. To probe the molecular groups at the interface,
surface-sensitive sum frequency generation spectroscopy was used to
show that aromatic and hydroxyl groups related to this protein content
at the adhesive interface could be playing a crucial role in adhesion.
On the basis of these results, we propose a model of the holdfast
architecture with similarities to the peptide cross-linking observed
in the peptidoglycan polymer of the bacterial cell wall. These results
not only provide information about the development of adhesives that
could be based on holdfast chemical architecture but also reveal a
potentially yet unexplored biosynthetic pathway in holdfast synthesis
that has not yet been revealed by genetic approaches, thereby opening
up a potentially new avenue of research in holdfast synthesis.