Crystal structure implies that cyclophilin predominantly catalyzes the trans to cis isomerization.
The crystal structure of human recombinant cyclophilin A complexed with a substrate of succinyl-Ala-Ala-Pro-Phe-p-nitroanilide (AAPF) has been determined and refined to an R-factor of 0.189 at 2.4 A resolution. The structure revealed only the cis form of the substrate bound to cyclophilin A in a stoichiometry of 1:1. This binding ratio is different from the structure of cyclophilin A complexed with the tetrapeptide N-acetyl-Ala-Ala-Pro-Ala-amidomethylcourmarin. Model docking revealed that the trans form of AAPF does not fit into the active site. The observation that only the trans cis form of AAPF binds to cyclophilin A implies that cyclophilin A predominantly catalyzes the trans to cis isomerization of a peptidylprolyl amide bond. On the basis of the structure, it is proposed that Arg55 hydrogen-bonds to the nitrogen to deconjugate the resonance of the prolyl amide bond and thus facilitates the cis-trans rotation.
Zhao
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Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill 27599, USA.
Ke
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H
D000591:Amino Acid Isomerases / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D003196:Computer Graphics; D003198:Computer Simulation; D003524:Cyclosporins / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D007536:Isomerism; D007700:Kinetics; D046911:Macromolecular Substances; D008958:Models, Molecular; D008961:Models, Structural; D008969:Molecular Sequence Data; D019696:Peptidylprolyl Isomerase; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity
D002352:Carrier Proteins; D003524:Cyclosporins; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase