Parravicini_2013_PLoS.One_8_e56254

Acyl aminoacyl peptidases are two-domain proteins composed by a C-terminal catalytic alpha/beta-hydrolase domain and by an N-terminal beta-propeller domain connected through a structural element that is at the N-terminus in sequence but participates in the 3D structure of the C-domain. We investigated about the structural and functional interplay between the two domains and the bridge structure (in this case a single helix named alpha1-helix) in the cold-adapted enzyme from Sporosarcina psychrophila (SpAAP) using both protein variants in which entire domains were deleted and proteins carrying substitutions in the alpha1-helix. We found that in this enzyme the inter-domain connection dramatically affects the stability of both the whole enzyme and the beta-propeller. The alpha1-helix is required for the stability of the intact protein, as in other enzymes of the same family; however in this psychrophilic enzyme only, it destabilizes the isolated beta-propeller. A single charged residue (E10) in the alpha1-helix plays a major role for the stability of the whole structure. Overall, a strict interaction of the SpAAP domains seems to be mandatory for the preservation of their reciprocal structural integrity and may witness their co-evolution.