Various Types of Polyampholyte Necklaces: Charge-in-Beads, Charge-in-Strings, and Hierarchical Structures

Polyampholytes are considered synthetic analogs of intrinsically disordered proteins (IDPs). In our previous work [1], we provided scaling predictions for single-chain conformations of charge-imbalanced Markov polyampholytes in theta solvent. Two distinct types of polyampholyte necklaces were predicted: charge-in-beads and charge-in-strings necklaces.



Herein, we corroborate the predictions of ref. [1] by molecular dynamics simulations. For the first time, the charge-in-strings necklace is detected in simulations. As the charge blockiness increases, the crossover between charge-in-beads and charge-in-strings necklaces occurs. This crossover is accompanied by a non-monotonic change in the number of globular beads, which is consistent with the theoretical predictions of ref. [1].



Further, we extend our theoretical framework to arbitrary solvent quality. Under poor solvent conditions and at high charge blockiness, a scaling region is found where a new, hybrid type of necklace is predicted. This hierarchical necklace can be viewed as a small classical necklace in ref. [2] forming within the charge-in-strings necklaces. Our findings can help understand the conformations of IDPs.



[1] Rumyantsev, A. M.; Johner, A.; de Pablo, J. J., ACS Macro Letter, 2021.

[2] Dobrynin, A. V.; Rubinstein, M.; Obukhov, S. P., Macromolecules, 1996.