Effects of endogenous cysteine proteinases on structures of collagen fibres from dermis of sea cucumber (Stichopus japonicus)

- Collagen fibres from sea cucumber were treated by endogenous cysteine proteinases.
- Collagen fibrils were disaggregated into collagen fibres by cysteine proteinases.
- Cysteine proteinases caused increasing structural disorder of collagen fibres.
- Cysteine proteinases freed glycosaminoglycan and hydroxyproline.

Autolysis of sea cucumber, caused by endogenous enzymes, leads to postharvest quality deterioration of sea cucumber. However, the effects of endogenous proteinases on structures of collagen fibres, the major biologically relevant substrates in the body wall of sea cucumber, are less clear. Collagen fibres were prepared from the dermis of sea cucumber (Stichopus japonicus), and the structural consequences of degradation of the collagen fibres caused by endogenous cysteine proteinases (ECP) from Stichopus japonicus were examined. Scanning electron microscopic images showed that ECP caused partial disaggregation of collagen fibres into collagen fibrils by disrupting interfibrillar proteoglycan bridges. Differential scanning calorimetry and Fourier transform infrared analysis revealed increased structural disorder of fibrillar collagen caused by ECP. SDS-PAGE and chemical analysis indicated that ECP can liberate glycosaminoglycan, hydroxyproline and collagen fragments from collagen fibres. Thus ECP can cause disintegration of collagen fibres by degrading interfibrillar proteoglycan bridges.