Archaea, have several adaptations that allow their cellular proteins to remain stable and active under the extreme environmental conditions. There is not one basic set of adaptations that works across all environments, instead Archaea have evolved protein features that are specifically adapted for each extreme environment.

Archaea can be categorized into three groups on the basis of protein adaptations: thermophilic, psychrophilic, and halophilic. Thermophilic proteins tend to have a prominent hydrophobic core and increased electrostatic interactions to maintain activity at higher temperatures. Psychrophilic proteins have a reduced hydrophobic core and a less charged protein surface to maintain flexibility and activity under cold temperatures. Halophilic proteins are characterized by increased negative surface charge due to increased acidic amino acid content and peptide insertions, which compensates for extreme ionic conditions.

It should be noted that acidophiles, alkaliphiles, and piezophiles are their own class of Archaeam, however protein adaptations toward pH and pressure are much less discernible.

Hope this partially helps,

Scott

I think as prokaryote their genes can easily structured for new adaptation

A unique and distinct S-layer (made of proteins) that provides chemical and physical protection, A completely different lipid profile of membrane, glycerol-ether lipids (not ester liker others), Unique enantiomers of glycerol, a differential tail structure of its lipids and occasional presence of a fused , more strong monolayer instead of bilayer are some of the features that make them so resilient.

Special membrane lipids and unique GC contact in DNA could offer some explanations!