Prevention of liposome cryoaggregation by a radish (Raphanus sativus L.) vacuolar calcium-binding protein (RVCaB).

Previously we found that the soluble fraction of radish (Raphanus sativus L.) taproots contained a large amount of an intrinsically disordered protein, which we identified as radish vacuolar calcium binding protein (RVCaB). Although RVCaB is known to inhibit cryo-damage to freeze-sensitive enzyme lactate dehydrogenase, there is no information on its cryoprotection of other types of macromolecules, such as biomembranes. In this study we found that RVCaB inhibited the cryoaggregation of phospholipid liposomes to a greater extent than common cryoprotectants, such as trehalose, glycine betaine, proline, bovine serum albumin (BSA), and polyethylene glycol (PEG). RVCaB inhibited the freeze/thaw-induced membrane fusion of liposomes. It became structurally disordered in solution, and this disorder was maintained in the presence of liposomes. Finally, the mechanism underlying RVCaB's inhibition of liposome cryoaggregation was discussed. • RVCaB is a major soluble protein in radish taproots. • RVCaB inhibited liposome cryoaggregation more efficiently than general protectants. • RVCaB prevented cryo-induced membrane fusion of liposomes. • The structural disorder of RVCaB may enhance its cryoprotection of liposomes. [ABSTRACT FROM AUTHOR]