Biophysical characterization of chitin-binding beak proteins in dosidicus gigas

• Main Author: Heymann, Dario Benjamin Jonas
• Other Authors: Ali Gilles Tchenguise Miserez
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials::Biomaterials
• Online Access: https://hdl.handle.net/10356/138896
• Institution: Nanyang Technological University

Carbohydrate-binding proteins (CBPs) are a versatile group of proteins occurring in almost every organism on earth. These proteins are imperative to various functions, ranging from enzymatic carbohydrate degradation and serve as templating scaffolds with load-bearing properties in the exoskeleton of crustaceans or insects. A large amount of data on how lectins bind highly specifically to carbohydrates exist, however, the actual binding mechanisms involved is unknown in most biological materials where they are found. Primary focus of the subsequent study is the determination of the structure of CBD-γ, a chitin-binding domain found in the Chitin-binding Beak Protein-3 (DgCBP-3) using NMR spectroscopy. DgCBP-3 is one of four unique chitin-binding proteins (DgCBPs) found in the beak structure of Dosidicus gigas and is believed to interact with chitin to form a net-like structure in which a second class of proteins, namely Histidine-binding Beak Proteins (DgHBPs) infiltrate to assemble the beak. Previous research has identified one chitin-binding motif, the extended Rebers and Riddiford” consensus (R&R), to play a critical step in the biogenesis and hardening process in exoskeletons of arthropods. However, till date no experimental tertiary structure of a protein containing an R&R Consensus has been reported and the mechanism how the R&R Consensus binds chitin remains unclear. The following study includes the structural determination of CBD-γ, which appears to be the first experimentally solved three-dimensional protein structure of a CBP containing the R&R Consensus. Further, solution state NMR spectroscopy has been used to elucidate the molecular interactions between CBD-γ and the soluble chitin derivative pentaacetyl-chitopentaose (PCP). The study shows that PCP triggers a folding of CBD-γ upon its interaction. The results of this study can be used as a template to understand in more details the role of the R&R motif and may inform other research conducted on other structural chitin-binding domains across species, including other cephalopods, crustaceans, and insects.