Potassium cations expand the conformation ensemble of β-amylase2 (BAM2).

The process for and regulatory mechanism controlling the synthesis and degradation of the polysaccharide starch are only superficially understood. β-amylases (BAMs) are enzymes that hydrolyze starch into maltose which is further used to drive metabolism and other cellular processes. Most BAMs in plants can function as monomeric enzymes and have hyperbolic kinetics. BAM2 from is unusual as it forms a homotetramer, displays sigmoidal kinetics, and is stimulated by the presence of potassium cations (K ). We used circular dichroism spectroscopy, small-angle X-Ray scattering, and molecular dynamics to investigate the effect of K on the structure of BAM2 and found that K induces the formation of an active conformation of BAM2 thereby increasing its activity.