Int J Mol Sci 2026 Jul 15;2714:. doi: 10.3390/ijms27146288.

Stable and Specific Multiprotein Complexes with High Molecular Masses in Different Organs of the Sea Cucumber Eupentacta fraudatrix.

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We have found for the first time several distinct, very large (1.25-1.69 megadaltons), stable protein-peptide complexes in various organs and tissues (upper body wall, gonads, respiratory trees, gut, and coelomic fluid) of the sea cucumber Eupentacta fraudatrix. It has been previously shown that complexes isolated from the whole organism are destroyed only under very harsh conditions. Here, for the first time, complexes were isolated from individual organs of the sea cucumber Eupentacta fraudatrix. According to gel filtration data, the molecular weights (MWs) of complexes from different organs are distinct but comparable (in kDa): 1690 ± 29 (coelomic fluid), 1650 ± 307 (gut), 1550 ± 253 (gonads), 1520 ± 140 (body wall), and 1250 ± 97 (respiratory trees). All complexes contain many of the same as well as different proteins with MWs of 10-20 kDa and >20 kDa. The number and type of proteins in the 10-20 kDa range vary among organs: body wall (20), gonads (19), coelomic fluid (16), gut (13), and respiratory trees (14). In addition, each complex contains specific proteins and peptides that are not present in complexes from other organs, and the number of such unique proteins also differs: body wall (13), gonads (7), respiratory trees (5), gut (4), and coelomic fluid (0). In the entire set of complexes isolated from the whole organism, 469 oligopeptides were identified, whereas only 370 peptides were detected in complexes from the five analyzed individual organs. The number of various peptides with MWs below 10 kDa in individual organ complexes decreases in the following order: body wall (134) > gut (115) > coelomic fluid (95) > respiratory trees (88) > gonads (70). These complexes contain both shared and distinct oligopeptides. Such highly stable complexes from different organs of sea cucumber Eupentacta fraudatrix have been isolated and characterized for the first time. In contrast to individual proteins and peptides, multiprotein complexes have expanded functional possibilities, as they can interact with various molecules and cells with which the individual proteins, enzymes, and peptides comprising the complexes can interact. Thus, they can perform the functions of all components located on their surfaces. One may suppose that many of the specific proteins, peptides, and enzymes within each complex are necessary for carrying out the specific biological functions of each individual organ.

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