The discovered chimeric protein plays the cohesive role to maintain scallop byssal root structural integrity

Pingping Xu,Dandan Wang,Yan Miao,Xiaokang Zhang,Bo Dong,Zhenmin Bao,Xiaoting Dai,Qianqian Lyu,Weizhi Liu,Shi Wang,Shuoshuo Wang,Luyao Teng

doi:10.1038/s41598-018-35265-y

Pingping Xu, Dandan Wang + Show 10 more

Open Access

https://doi.org/10.1038/s41598-018-35265-y

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Journal: Scientific Reports	Publication Date: Nov 20, 2018
Citations: 8	License type: open-access

Affiliation: Ocean University of China

Abstract

Adhesion is essential for many marine sessile organisms. Unraveling the compositions and assembly of marine bioadheisves is the fundamental to understand their physiological roles. Despite the remarkable diversity of animal bioadhesion, our understanding of this biological process remains limited to only a few animal lineages, leaving the majority of lineages remain enigmatic. Our previous study demonstrated that scallop byssus had distinct protein composition and unusual assembly mechanism apart from mussels. Here a novel protein (Sbp9) was discovered from the key part of the byssus (byssal root), which contains two Calcium Binding Domain (CBD) and 49 tandem Epidermal Growth Factor-Like (EGFL) domain repeats. Modular architecture of Sbp9 represents a novel chimeric gene family resulting from a gene fusion event through the acquisition of CBD2 domain by tenascin like (TNL) gene from Na+/Ca2+exchanger 1 (NCX1) gene. Finally, free thiols are present in Sbp9 and the results of a rescue assay indicated that Sbp9 likely plays the cohesive role for byssal root integrity. This study not only aids our understanding of byssus assembly but will also inspire biomimetic material design.

Highlights

Underwater bioadhesion is an essential biological process for marine sessile organisms, which is believed to be critical for movement, food procurement, self-defense, metamorphosis, and attachment[1,2,3]
It is known that some scallop species are able to attach to the substratum through a byssus with remarkably unique morphology[9], the scallop byssus is analogous to mussel byssus
To study the sequence features of the Epidermal Growth Factor-Like (EGFL) derived from Sbp[9], multiple sequence alignments among all 49 EGFL domains were carried out, and the results show that one significant feature of these conserved EGFL repeats is the presence of the PCGGPC motif at the first two Cys residues (Supplementary Fig. S3), which is quite similar to the predominant subrepeat of GPGGX in flagelliform silk[18]

Summary

Results and Discussion

Root region of scallop byssus exhibits unique mechanical and ultrastructural properties. One possible explanation is the presence of extra EGFL4 sacrifices itself by consuming residual DTT, the byssal root region is able to partially recover the original structure Another possible explanation is free Cys in the EFGL4 can form covalent bonds with neighboring byssal fibers through formation of either the disulfide or the Dopa-quinone[28], which both extensively exist in scallop byssus[11]. Previous study has shown that the EGFL domain in TN-X is important for the interaction with collagen[29] These observations suggest that Sbp[9] may play a cohesive role as the cross-linker that is responsible for structural integrity of scallop byssal root. Metal ions present in seawater, especially Ca2+, are able to alter the protein self-assembly properties to further strengthen these interactions and can function as a “trigger”

Conclusions

Author Contributions

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