Ambiguity between Adaptation and Aggregation of Intrinsically Disordered Fish Proteins: Antifreeze-like or Amyloid-like?

Antifreeze proteins (AFPs) play a crucial role in the survival of fish species by inhibiting ice crystal growth. In this study, a comprehensive in silico characterization of an uncharacterized AFP sequence from Arctogadus glacialis along with other fishes was performed. Sequence analysis revealed the presence of extensive tandem repeats, suggesting a modular architecture typical of AFPs. The predicted molecular weight of the protein was 185.1 kDa, with a theoretical isoelectric point ranging between 5.54 and 5.73 and a net charge of − 16.5 at pH 7.0. Amino acid composition analysis indicated threonine (8.6%) and leucine (8.2%) as the most abundant residues, while tryptophan (0.9%) and lysine (1.2%) were least represented. The protein exhibited an aliphatic index of 75.79, a GRAVY value of − 0.147, and an instability index of 52.13, suggesting moderate thermostability and hydrophilicity. Secondary structure prediction indicated a predominance of random coils (53.65%) in the protein; comparative analysis showed a higher random coil (57.54%) structure in lamprey AFPs. Tertiary structure modeling yielded a pTM score of 0.43, supporting a partially ordered structure with flexible loop regions. Conserved domain analysis identified a key motif spanning residues 1471–1520, potentially involved in ice-binding. Phylogenetic analysis of AFPs from host and parasitic fish species revealed evolutionary clustering consistent with adaptation to unfamiliar environments. Collectively, these findings provide the first computational insights into the structural and functional features of A. glacialis AFP, contributing to the broader understanding of antifreeze mechanisms among fishes.