PhD Open Defense – Angelico Raphael Obille

Abstract: While it remains challenging to engineer strong, biocompatible adhesives that are effective in wet conditions, many aquatic organisms have evolved strategies to adhere to surfaces underwater. Zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) are freshwater bivalves that use a proteinaceous structure called the byssus to permanently attach to diverse surfaces. Although superficially similar to the marine mussel byssus, the Dreissenid byssal system evolved in freshwater conditions, resulting in a unique, and understudied, biochemical profile. Understanding the mechanism of byssal adhesion employed by Dreissenids offers potential new insights for the development of bioinspired adhesive materials. The objective of this thesis is to identify and functionally characterize Dreissenid adhesive proteins that directly interface with adherend surfaces. Localization via quantitative proteomics of quagga mussel byssal proteins revealed a set of 20 putatively adhesive footprint proteins. Among these was Dbfp7, a highly expressed small polymorphic protein that was shown to exhibit adhesive ability in aqueous conditions despite lacking significant amounts of 3,4-dihydroxyphenylalanine (DOPA). A sequence-reductive approach combined with atomic force nanomechanical mapping and surface-enhanced Raman spectroscopy revealed functional differences between domains of Dbfp7, revealing sequences that encode adhesive properties. The identification and characterization of Dbfp7 expands the repertoire of known wet adhesive proteins, furthers our understanding of freshwater bioadhesion, and provides a new source of inspiration for the development of improved bioinspired wet adhesive materials for applications including medical adhesives.