PDBsum entry 1ihg

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Isomerase PDB id
Protein chain
364 a.a. *
Waters ×489
* Residue conservation analysis

References listed in PDB file
Key reference
Title Two structures of cyclophilin 40: folding and fidelity in the tpr domains.
Authors P.Taylor, J.Dornan, A.Carrello, R.F.Minchin, T.Ratajczak, M.D.Walkinshaw.
Ref. Structure, 2001, 9, 431-438. [DOI no: 10.1016/S0969-2126(01)00603-7]
PubMed id 11377203
BACKGROUND: The "large immunophilin" family consists of domains of cyclophilin or FK506 binding protein linked to a tetratricopeptide (TPR) domain. They are intimately associated with steroid receptor complexes and bind to the C-terminal domain of Hsp90 via the TPR domain. The competitive binding of specific large immunophilins and other TPR-Hsp90 proteins provides a regulatory mechanism for Hsp90 chaperone activity. RESULTS: We have solved the X-ray structures of monoclinic and tetragonal forms of Cyp40. In the monoclinic form, the TPR domain consists of seven helices of variable length incorporating three TPR motifs, which provide a convincing binding surface for the Hsp90 C-terminal MEEVD sequence. The C-terminal residues of Cyp40 protrude out beyond the body of the TPR domain to form a charged helix-the putative calmodulin binding site. However, in the tetragonal form, two of the TPR helices have straightened out to form one extended helix, providing a dramatically different conformation of the molecule. CONCLUSIONS: The X-ray structures are consistent with the role of Cyclophilin 40 as a multifunctional signaling protein involved in a variety of protein-protein interactions. The intermolecular helix-helix interactions in the tetragonal form mimic the intramolecular interactions found in the fully folded monoclinic form. These conserved intra- and intermolecular TPR-TPR interactions are illustrative of a high-fidelity recognition mechanism. The two structures also open up the possibility that partially folded forms of TPR may be important in domain swapping and protein recognition.
Figure 5.
Figure 5. Stereo Picture of the Main Intermolecular Interaction in the Tetragonal Form of Cyp40 and an Overlay of the Folding Intermediate Dimer and the Fully Folded Conformer(a) The partially unfolded TPR domains form a symmetrical dimer. One molecule is colored as in Figure 3b, and the partner molecule is colored red. The first TPR, comprising helices P and Q (shown in the boxed region), make an intermolecular contact with helix R' of the dimer-related molecule.(b) The boxed region of (b), with the same color scheme, showing helices P, Q, and R' for the tetragonal form, overlaid with helices P, Q, and R (yellow) of the folded TPR domain of the monoclinic form. The intra- and intermolecular interactions of helix R with helices P and Q are seen to be nearly identical

The above figure is reprinted by permission from Cell Press: Structure (2001, 9, 431-438) copyright 2001.
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