posted on 2024-02-24, 16:07authored byTu Anh Nguyen, ChangWoo Lee
This study investigates
the impact of aromatic–aromatic
interactions on the cold adaptation of thioredoxin (Trx), a small
redox protein with a conserved Trx-fold structure. Two Trx orthologs,
one from the psychrophilic Arctic bacterium Sphingomonas sp. (SpTrx) and the other from the mesophilic Escherichia
coli (EcTrx), display distinct aromatic interactions
in their α1,α3-helices. SpTrx features a larger Trp11-Phe69
pair, while EcTrx employs a smaller Phe12-Tyr70 pair along with an
additional Asp9-Thr66 hydrogen bond. Smaller aromatic residues in
SpTrx (Phe-Phe or Phe-Tyr pair) lead to decreased thermal and thermodynamic
stabilities, increased conformational flexibility, and reduced enzyme
activity. In contrast, EcTrx’s thermal stability is primarily
influenced by the larger Trp residue, especially in the more hydrophobic
Trp-Phe pair compared to the Trp-Tyr pair. Both SpTrx and EcTrx exhibit
a strengthening of the Asp-Thr hydrogen bond by a Phe-Tyr pair and
a weakening by a Trp-Phe pair. Additionally, the Asp8-Thr65 hydrogen
bond in SpTrx contributes to the destabilization of the Phe-Phe pair.
Molecular dynamics simulations of SpTrx indicate that a smaller aromatic
pair or the Asp-Thr hydrogen bond in the α1,α3-helices
further destabilizes the α2-helix across the central β-sheet.
Our results suggest that the Thr-to-Ala mutation destabilizes the
α1,α3-helices, resulting in a larger aromatic pair and
reduced packing density in psychrophilic Trxs during cold adaptation.
These findings enhance our understanding of Trx’s adaptation
to colder temperatures.