Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange
Abstract
Chitin is the second most abundant biopolymer found in nature and is present predominantly in the exoskeleton, endoskeleton, and cell wall of many organisms. It has great economic value for its properties and is extensively used for industrial and biomedical purposes. Chitin-protein composites in different organisms are usually localized in their external shells and are heavily mineralized. Self-assembly of shells from mollusks, arthropods and cephalopods is of fundamental interest to understand evolutionary diversity and learn construction mechanisms from nature to promote assembly of new materials with commercial applications. It is difficult to study natural assembly of complex chitin-protein composites, and very little is known so far. To learn how chitin and proteins are assembled into 3- dimensional weight-bearing structures it would be ideal to study a simple chitinous structure comprised of hydrated chitin without metals that could be studied at the cellular and molecular level from its embryonic origin and also easily extracted in bulk quantity from the adult. The pen or gladius of D. pealeii is one such example. While most chitinbearing structures are external to the organism’s anatomy, the pen of the squid is constructed internally. The pen is a translucent, tough, yet flexible skeletal element, involved with maintaining the structure of the mantle during jet propulsion. It is a multilamellar assembly of chitin and protein without mineralization or sclerotization. We have identified that the pen is constructed with chitin and very few proteins. We have studied the 20 most abundant embedded proteins in the chitin-protein composite in the pen. While we have identified some of these proteins, many of them remain to be characterized. We have used microscopy, CP-NMR, RACE PCR, and different bioinformatics tools to characterize and obtain full-length sequences for the proteins. We have used the transcriptome, proteome and genome of D. pealeii to assemble the building blocks of the gladius. We compare these protein sequences with the predicted sequences in the genomes of the elusive giant squid, Architeuthis dux, and the bobtail squid, Euprymna scolopes. The giant squid, like D. pealeii assembles a gladius, while the bobtail squid does not. This unique comparison has enabled us to identify protein sequences that appear unique to the construction of squid gladii. These efforts will be used to help identify the chemistry behind the cellular attachment to chitin as well as chemical modifications to promote chitin as a printable scaffold for tissue engineering
