Abstract
Barnacle adhesion is a focus for fouling-control technologies as well as the development of bioinspired adhesives, although the mechanisms remain very poorly understood. The barnacle cypris larva is responsible for surface colonisation. Cyprids release cement from paired glands that contain proteins, carbohydrates and lipids, although further compositional details are scant. Several genes coding for cement gland-specific proteins were identified, but only one of these showed database homology. This was a lysyl oxidase-like protein (lcp_LOX). LOX-like enzymes have been previously identified in the proteome of adult barnacle cement secretory tissue. We attempted to produce recombinant LOX in E. coli, in order to identify its role in cyprid cement polymerisation. We also produced two other cement gland proteins (lcp3_36k_3B8 and lcp2_57k_2F5). lcp2_57k_2F5 contained 56 lysine residues and constituted a plausible substrate for LOX. While significant quantities of soluble lcp3_36k_3B8 and lcp2_57k_2F5 were produced in E. coli, production of stably soluble lcp_LOX failed. A commercially sourced human LOX catalysed the crosslinking of lcp2_57k_2F5 into putative dimers and trimers, and this reaction was inhibited by lcp3_36k_3B8. Inhibition of the lcp_LOX:lcp2_57k_2F5 reaction by lcp3_36k_3B8 appeared to be substrate specific, with no inhibitory effect on the oxidation of cadaverine by LOX. The results demonstrate a possible curing mechanism for barnacle cyprid cement and, thus, provide a basis for a more complete understanding of larval adhesion for targeted control of marine biofouling and adhesives for niche applications.
Highlights
Barnacles are well-known for their ability to remain attached throughout their adult life
The present study identified a range of uncharacterised proteins within the cyprid cement gland and attempted their recombinant production in Escherichia coli
The amount of hydrogen peroxide generated was calculated from the difference between the end point of fluorescence signals of identical samples incubated in the presence and absence of lysyl oxidase (LOX)
Summary
Barnacles are well-known for their ability to remain attached throughout their adult life. Can live for many years and throughout this period their adhesive bond survives biodegradation and exposure-immersion cycles, and accommodates growth of the animal, adapting to the morphology of the substratum. The adhesive bond must be sufficiently strong to resist removal by predators and the local hydrodynamics, and compatible with a diverse range of natural surfaces that may be selected by the settling larva, the cyprid (Aldred and Clare 2008). Several decades of research into the adhesion of adult barnacles have improved understanding of their dynamic adhesion process with a view to preventing barnacle adhesion on artificial structures at sea (antifouling) and/or developing synthetic adhesives with niche capabilities (bioadhesion). The fundamentals of barnacle adhesion remain poorly understood (Liang et al 2019; Davey et al 2021)
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