The functional domains of the chloroplast unusual positioning protein 1

Chloroplasts of plants move in response to variations in light intensity. One protein involved in this process is the chloroplast unusual positioning protein 1-CHUP1, which is anchored in the outer membrane of the organelle. The protein is able to interact with actin and profilin and might coordinate actin filament reformation and thereby chloroplast repositioning. However, molecular details on this action have not been presented so far. Here, we demonstrate that CHUP1 is able to homo-dimerize and that this dimerization is dependent on the N-terminal coiled-coil domain. The leucine zippers, which are present in the N-terminal and C-terminal portion of the protein, are involved in the formation of intra-molecular interactions. Based on this we propose that CHUP1 functions as a dimer and that intra-molecular structure formation might result in a close proximity of the proline rich domain involved in profilin binding and the actin binding domain.