Abstract
The barnacle, Amphibalanus amphitrite, is a common marine fouling organism. Understanding the mechanism of barnacle adhesion will be helpful in resolving the fouling problem. Barnacle cement is thought to play a key role in barnacle attachment. Although several adult barnacle cement proteins have been identified in Megabalanus rosa, little is known about their function in barnacle settlement. In this study, two homologous 20k-cement proteins (cp20k) in Amphibalanus amphitrite, named Bamcp20k-1 and Bamcp20k-2, were characterized. The two homologues share primary sequence structure with proteins from other species including Megabalanus rosa and Fistulobalanus albicostatus. The conserved structure included repeated Cys domains and abundant charged amino acids, such as histidine. In this study we demonstrated that Bamcp20k-1 localized at the α secretory cells in the cyprid cement gland, while Bamcp20k-2 localized to the β secretory cells. The differential localizations suggest differential regulation for secretion from the secretory cells. Both Bamcp20k-1 and Bamcp20k-2 from cyprids dissolved in PBS. However, adult Bamcp20k-2, which was dominant in the basal shell of adult barnacles, was largely insoluble in PBS. Solubility increased in the presence of the reducing reagent Dithiothreitol (DTT), suggesting that the formation of disulfide bonds plays a role in Bamcp20k-2 function. In comparison, Bamcp20k-1, which was enriched in soft tissue, could not be easily detected in the shell and base by Western blot and easily dissolved in PBS. These differential solubilities and localizations indicate that Bamcp20k-1 and Bamcp20k-2 have distinct functions in barnacle cementing.
Highlights
Amphibalanus amphitrite, an inter-tide marine organism, is a common fouling animal found all over the world
Bamcp20k-1 was enriched in the soft tissue and soluble in phosphate-buffered saline (PBS) buffer
Bamcp20-2 was predominately present in the base plate and was insoluble in PBS even in the presence of 500 mM DTT
Summary
Amphibalanus amphitrite, an inter-tide marine organism, is a common fouling animal found all over the world. Understanding how the barnacles glue themselves to substrata is essential. The barnacle is a bi-phase crustacean with a planktonic phase and a sessile phase (Fig. 1). The planktonic phase is composed of six feeding nauplius stages and one non-feeding cyprid stage. The cyprid stage is critical for the barnacle from planktonic to sessile phase. Once a site is selected, the cyprid releases adhesive called cement that it uses to glue itself onto the substratum. As the juvenile matures into an adult the cement between the barnacle and the substratum becomes much stronger
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