The Quantitative Proteome of the Cement and Adhesive Gland of the Pedunculate Barnacle, Pollicipes pollicipes

Abstract

Adhesive secretion has a fundamental role in barnacles’ survival, keeping them in an adequate position on the substrate under a variety of hydrologic regimes. It arouses special interest for industrial applications, such as antifouling strategies, underwater industrial and surgical glues, and dental composites. This study was focused on the goose barnacle Pollicipes pollicipes adhesion system, a species that lives in the Eastern Atlantic strongly exposed intertidal rocky shores and cliffs. The protein composition of P. pollicipes cement multicomplex and cement gland was quantitatively studied using a label-free LC-MS high-throughput proteomic analysis, searched against a custom transcriptome-derived database. Overall, 11,755 peptide sequences were identified in the gland while 2880 peptide sequences were detected in the cement, clustered in 1616 and 1568 protein groups, respectively. The gland proteome was dominated by proteins of the muscle, cytoskeleton, and some uncharacterized proteins, while the cement was, for the first time, reported to be composed by nearly 50% of proteins that are not canonical cement proteins, mainly unannotated proteins, chemical cues, and protease inhibitors, among others. Bulk adhesive proteins accounted for one-third of the cement proteome, with CP52k being the most abundant. Some unannotated proteins highly expressed in the proteomes, as well as at the transcriptomic level, showed similar physicochemical properties to the known surface-coupling barnacle adhesive proteins while the function of the others remains to be discovered. New quantitative and qualitative clues are provided to understand the diversity and function of proteins in the cement of stalked barnacles, contributing to the whole adhesion model in Cirripedia.

Proteogenomic Characterization of the Cement and Adhesive Gland of the Pelagic Gooseneck Barnacle Lepas anatifera

“…However, in our opinion, this classification has various drawbacks, since it does not provide accurate information of the CPs diversity, nor a proper definition of CPs family. Moreover, the more CPs are identified, featuring different molecular weights, the bigger the confusion for naming the CPs and CP families, as naming is based on weight, and particularly since high throughput proteomics has been applied to the analysis of cirripede adhesives, several new proteins with an enormous variety of molecular weights have been described [ 12 , 13 , 14 , 15 , 16 , 17 ]. CPs may have a quite different weight, while featuring very similar physicochemical properties and amino acid relative abundance, which causes their clustering in principal components analyses [ 17 ].…”

“…In some cases (e.g., CP19k and CP20k; surface coupling proteins) they may have similar weight and feature very different physicochemical properties and amino acid relative abundance. In Pollicipes pollicipes several putative CPs were recently reported in the cement, with a variety of molecular weights [ 15 ]. Intriguingly these barnacle CPs did not show any homology with other marine adhesive proteins [ 11 , 12 ], or other proteins at all, possessing no identifiable protein domains, being in some cases structurally very disordered, and that could not be named in the previously defined CP’s nomenclature.…”

“…Intriguingly these barnacle CPs did not show any homology with other marine adhesive proteins [ 11 , 12 ], or other proteins at all, possessing no identifiable protein domains, being in some cases structurally very disordered, and that could not be named in the previously defined CP’s nomenclature. This puts a limitation to name the new CPs identified, specifically the interfacial ones, which seems to be more diverse [ 15 ]. Despite the updating of the general model of barnacle adhesion in the last years [ 16 , 18 , 19 ], the current CPs classification is becoming obsolete with the discover of new CPs [ 15 ].…”

“…This puts a limitation to name the new CPs identified, specifically the interfacial ones, which seems to be more diverse [ 15 ]. Despite the updating of the general model of barnacle adhesion in the last years [ 16 , 18 , 19 ], the current CPs classification is becoming obsolete with the discover of new CPs [ 15 ]. Barnacles’ adhesive secretion mechanism remains misunderstood, and CPs misclassified.…”

“…The combination of transcriptomic and proteomic approaches has resulted in a powerful tool for a high throughput discovery of barnacle’s CPs [ 15 ]. Thus, this study was focused on the proteogenomic characterization of L. anatifera ( Figure 1 ) adhesion system.…”