Crystal structure of AmyA lacks acidic surface and provide insights into protein stability at poly-extreme condition.

Here we report the first crystal structure of a protein, AmyA, a secretory alpha-amylase isolated from Halothermothrix orenii, which is both halophilic and thermophilic. The crystal structure was determined at 1.6 A resolution. AmyA lacks the conserved acidic surface, which is considered essential for protein stability at high salinity. Sedimentation velocity and CD experiments on AmyA reveal the formation of unique reversible poly-dispersed oligomers that show unusually high thermal stability. These studies provide valuable insight into the structural elements that contribute to the stability of AmyA at both physical and chemical extremes and their functional implications.