Purification and Preliminary X-Ray Crystallographic Analysis of the Peptidyl-Prolyl cis-trans Isomerase Alr5059 from Anabaena sp. PCC 7120

Peptidyl-prolyl cis-trans isomerases (PPIases) have a wide range of functions in all cells. They are typically classified as cyclophilin, the FK506-binding protein-like or parvulins. Most PPIases are two-domain enzymes. While the peptidyl-prolyl cis-trans isomerase domain is common to all PPIlases, different proteins differ in the function of the second domain. Plant PPIases of the cyclophilin family (Cyp38 in A. thaliana) contain a second domain at the N-terminus, but its function is still not known. They are localized in the thylakoid lumen and are involved in the assembly of photosystem II. The protein is conserved among plants and cyanobacteria with high similarity in the PPIase domain, but with some divergence in the N-terminal region of the protein. This prompted protein crystallization to analyze whether a unique feature of plant proteins originates from a cyanobacterial ancestor. We expressed the Alr5059 protein from Anabaena sp. PCC 7120 in E. coli and crystallized protein by the sitting drop method. Single crystals of the Alr5059 protein appeared after 5-7 days. The best crystal gave a diffraction pattern to a resolution of 1.1 angstrom. The crystal belongs to the monoclinic space group P12(1)1 with unit cell parameters a = 41.2 angstrom, b = 103.2 angstrom, c = 44.2 angstrom and beta = 114.7 degrees and contains one molecule per asymmetric unit.