  Protein aggregates exhibit diverse morphology, exemplified by amyloid
fibrils, gel-like structures, and liquid-like condensates. Differences in the
morphologies in identical proteins play important functional roles in several
diseases. Simulations using a minimal model show that such structures are
encoded in the sequence complexity and bending rigidity of the monomers. The
low-complexity flexible sequences form liquid droplets, whose relaxation
dynamics are ergodic. In contrast, rigid low and high-complexity sequences,
which form ordered nematic fibril-like structures and amorphous aggregates,
exhibit heterogenous, non-ergodic dynamics. The relaxation times under these
conditions increase as the waiting time increases, which is a signature of
aging. The implications of our findings for aging in intrinsically disordered
proteins and repeat RNA sequences are outlined.
