Functional Divergence of Mucus in Pacific Oyster ( <i>Crassostrea gigas</i> ): Insights From Integrated Proteomic and Rheological Study

Crassostrea gigas survives in the intertidal zone by relying on tissue-specific mucus secreted by different organs. However, the macroscopic differentiation of mucus physical properties and their molecular mechanisms remain poorly understood. Here, we integrated proteomics and rheological analysis to investigate the molecular basis potentially underlying the viscosity hierarchy of mucus and its functional match across three key tissues (mantle, labial palps, and gill) in the C. gigas. Proteomic analysis suggested that varying levels of extracellular matrix (ECM) components and glycosaminoglycan (GAG) synthesis are closely associated with this physical hierarchy. Specifically, active GAG synthesis and high ECM enrichment in the labial palps are consistent with a dense hydrated gel network. In contrast, progressively lower ECM accumulation and downregulated carbohydrate metabolism in the mantle and gill correlate with weaker hydrogen bond networks. Rheological characterization suggested a clear viscosity hierarchy that is consistent with each tissue's physiological role: labial palps mucus displayed the highest complex viscosity (0.046 Pa·s), reflecting properties that may contribute to feeding; mantle mucus exhibits elastic-dominant suitable for surface protection; and gill mucus showed the lowest viscosity (0.028 Pa·s), which is consistent with facilitating gas exchange. Ultimately, this study indicates that tissue-specific molecular and metabolic profiles are associated with mucus viscoelasticity to meet physiological requirements. These findings not only provide insight into the tissue-specific molecular basis of mucus viscosity in C. gigas, but also provide inspiration for designing marine bionic intelligent hydrogels and the development of anti-corrosion coatings, addressing longstanding challenges in offshore engineering.