Crystal Structure of Arabidopsis Cyclophilin38 Reveals a Previously Uncharacterized Immunophilin Fold and a Possible Autoinhibitory Mechanism

Department of Biological Sciences, National University of Singapore, Singapore 117543.
The Plant Cell (Impact Factor: 9.34). 06/2012; 24(6):2666-74. DOI: 10.1105/tpc.111.093781
Source: PubMed


Cyclophilin38 (CYP38) is one of the highly divergent cyclophilins from Arabidopsis thaliana. Here, we report the crystal structure of the At-CYP38 protein (residues 83 to 437 of 437 amino acids) at 2.39-Å resolution. The structure reveals two distinct domains: an N-terminal helical bundle and a C-terminal cyclophilin β-barrel, connected by an acidic loop. Two N-terminal β-strands become part of the C-terminal cyclophilin β-barrel, thereby making a previously undiscovered domain organization. This study shows that CYP38 does not possess peptidyl-prolyl cis/trans isomerase activity and identifies a possible interaction of CYP38 with the E-loop of chlorophyll protein47 (CP47), a component of photosystem II. The interaction of CYP38 with the E-loop of CP47 is mediated through its cyclophilin domain. The N-terminal helical domain is closely packed together with the putative C-terminal cyclophilin domain and establishes a strong intramolecular interaction, thereby preventing the access of the cyclophilin domain to other proteins. This was further verified by protein-protein interaction assays using the yeast two-hybrid system. Furthermore, the non-Leucine zipper N-terminal helical bundle contains several new elements for protein-protein interaction that may be of functional significance. Together, this study provides the structure of a plant cyclophilin and explains a possible mechanism for autoinhibition of its function through an intramolecular interaction.

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    • "The HCF136 protein is a prerequisite for the assembly of PSII reaction centers during complex biogenesis, while CYP38 assists the assembly of PSII core complexes during both biogenesis and repair (Meurer et al., 1998; Plucken et al., 2002; Fu et al., 2007; Sirpio et al., 2008). The C-terminal CYP-like domain of CYP38 interacts with the PSII apoprotein, CP47 (Vasudevan et al., 2012). Thus, CYP38 might assist the correct folding and integration of CP47 into the PSII core. "
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