A cation-binding protein of Arabidopsis thaliana AtPCaP1 has a unique cation-binding property and Cu²⁺-induced structural change.

Abstract

AtPCaP1 is localized to plasma membrane via N-myrisotylation and association with PI(3,5)P₂. The protein is composed of 225 amino acid residues and rich in Glu and Lys. No enzymatic functional motif was found in AtPCaP1. The physiological function is unclear. In the present study, we prepared the recombinant AtPCaP1 to determine its cation-binding properties. By CD spectrum and DSC (differential scanning calorimeter) analyses, AtPCaP1 has been revealed to have unique properties: namely, the binding of divalent cations and the high protein concentrations decreased the thermal denaturation temperature. In other words, these conditions decreased heat stability of AtPCaP1. Furthermore, AtPCaP1 specifically changed higher-order structure by binding of Cu²⁺. Interestingly, it binds 8 Cu²⁺ ions per molecule with K_d of 10 μM even though AtPCaP1 has no His or Cys, We will report more detailed information and discuss its physiological role.