Human RNase 1 can extensively oligomerize through 3D domain swapping thanks to the crucial contribution of its C-terminus

Human ribonuclease (RNase) 1 and bovine RNase A are the proto-types of the secretory pancreatic-type (pt)RNase super-family. RNase A can oligomerize through the 3D domain swapping (DS) mechanism upon acetic acid (HAc) lyophilisation, producing enzymatically active oligomeric conformers by swapping both N- and Ctermini. Also some RNase 1 mutants were found to self-associate through 3D-DS, however forming only Nswapped dimers. Notably, enzymatically active dimers and larger oligomers of wt-RNase 1 were collected here, in higher amount than RNase A, from HAc lyophilisation. In particular, RNase 1 self-associates through the 3D-DS of its Nterminus and, at a higher extent, of the C-terminus. Since RNase 1 is four-residues longer than RNase A, we further analyzed its oligomerization tendency in a mutant lacking the last four residues. The C-terminus role has been investigated also in amphibian onconase (ONC & REG;), a pt-RNase that can form only a N-swapped dimer, since its C-terminus, that is three-residues longer than RNase A, is locked by a disulfide bond. While ONC mutants designed to unlock or cut this constraint were almost unable to dimerize, the RNase 1 mutant self-associated at a higher extent than the wt, suggesting a specific role of the C-terminus in the oligomerization of different RNases. Overall, RNase 1 reaches here the highest ability, among pt-RNases, to extensively self-associate through 3DDS, paving the way for new investigations on the structural and biological properties of its oligomers.

Automated summary

Human RNase 1 and bovine RNase A are prototypes of the pt-RNase superfamily and can oligomerize through the 3D domain swapping mechanism. RNase 1 self-associates through the 3D-DS of its N- and C-termini, while RNase A only forms N-swapped dimers. RNase 1 exhibits a higher tendency to self-associate than RNase A, and its C-terminus plays a specific role in the oligomerization of different RNases.