Ribonucleases of Very Stable Multi-Protein Complexes from Different Organs of Sea Cucumber Paracaudina chilensis

Ribonuclease (RNase) activity, which mediates RNA degradation, plays a critical role in the development and survival of various organisms. In this study, we for the first time performed a comprehensive analysis of ribonuclease activity within highly stable multi-protein complexes isolated from five different organs of the holothurian Paracaudina chilensis (coelomic fluid, body wall, gut, gonads, and respiratory trees). Previously, these complexes were shown to have molecular masses ranging from 1.2 to 1.8 MDa and to differ in their protein–peptide composition. Using zymography, we identified enzymatically active protein bands with apparent molecular masses ranging from approximately 10 to 180 kDa within these complexes, which exhibited RNase activity at pH values from 3.5 to 9.5. The number of detectable activities differed among organs: the greatest diversity (13 distinct RNA-hydrolyzing activities detected under at least one set of conditions) was observed in the complex from coelomic fluid, whereas the complexes from body wall and gut contained the lowest numbers (5 and 6, respectively). Each complex was characterized by a set of RNase catalytic activities that differed in optimal pH (in the presence of 5 mM MgCl2), the number of apparent pH optima per band (from one to four), and sensitivity to metal ions (Mg2+, Mn2+, Zn2+, Co2+, Ca2+, and Ni2+). Some RNase activities were activated by a single metal ion, while others responded to multiple ions. The obtained data demonstrate that preparations of stable multiprotein complexes contain diverse sets of RNA-hydrolyzing activities, but the individual enzymes responsible for these activities remain unidentified. Given the outstanding regenerative capacity of holothurians and the involvement of RNases in the regulation of gene expression and RNA processing, it is suggested that the detected sets of RNase activities may play important roles in tissue regeneration, immune defense, and other physiological processes. This work opens new perspectives for studying the functional role of stable multiprotein complexes in marine invertebrates and highlights the need for further investigation of their catalytic potential.