Conformational response to charge clustering in synthetic intrinsically disordered proteins

Background: Recent theoretical and computational studies have shown that the charge content and, most importantly, the linear distribution of opposite charges are major determinants of conformational properties of intrinsically disordered proteins (IDPs). Charge segregation in a sequence can be measured through kappa, which represents a normalized measure of charge asymmetry. A strong inverse correlation between kappa and radius of gyration has been previously demonstrated for two independent sets of permutated IDP sequences. Methods: We used two well-characterized IDPs, namely measles virus N-TAIL and Hendra virus PNT4, sharing a very similar fraction of charged residues and net charge per residue, but differing in proline (Pro) content. For each protein, we have rationally designed a low- and a high-kappa variant endowed with the highest and the lowest kappa values compatible with their natural amino acid composition. Then, the conformational properties of wild-type and kappa-variants have been assessed by biochemical and biophysical techniques. Results: We confirmed a direct correlation between kappa and protein compaction. The analysis of our original data along with those available from the literature suggests that Pro content may affects the responsiveness to charge clustering. Conclusions: Charge clustering promotes IDP compaction, but the extent of its effects depends on the sequence context. Proline residues seem to play a role contrasting compaction. General significance: These results contribute to the identification of sequence determinants of IDP conformational properties. They may also serve as an asset for rational design of non-natural IDPs with tunable degree of compactness.