Structural Insights into Substrate Binding by <i>Pv</i> FKBP35, a Peptidylprolyl <i>cis-trans</i> Isomerase from the Human Malarial Parasite Plasmodium vivax

<jats:title>ABSTRACT</jats:title> <jats:p> The immunosuppressive drug FK506 binding proteins (FKBPs), an immunophilin family with the immunosuppressive drug FK506 binding property, exhibit peptidylprolyl <jats:italic>cis-trans</jats:italic> isomerase (PPIase) activity. While the cyclophilin-catalyzed peptidylprolyl isomerization of X-Pro peptide bonds has been extensively studied, the mechanism of the FKBP-mediated peptidylprolyl isomerization remains uncharacterized. Thus, to investigate the binding of FKBP with its substrate and the underlying catalytic mechanism of the FKBP-mediated proline isomerization, here we employed the FK506 binding domain (FKBD) of the human malarial parasite <jats:named-content content-type="genus-species">Plasmodium vivax</jats:named-content> FK506 binding protein 35 ( <jats:italic>Pv</jats:italic> FKBP35) and examined the details of the molecular interaction between the isomerase and a peptide substrate. The crystallographic structures of apo <jats:italic>Pv</jats:italic> FKBD35 and its complex with the tetrapeptide substrate succinyl-Ala-Leu-Pro-Phe- <jats:italic>p</jats:italic> -nitroanilide (sALPFp) determined at 1.4 Å and 1.65 Å resolutions, respectively, showed that the substrate binds to <jats:italic>Pv</jats:italic> FKBD35 in a <jats:italic>cis</jats:italic> conformation. Nuclear magnetic resonance (NMR) studies demonstrated the chemical shift perturbations of D55, H67, V73, and I74 residues upon the substrate binding. In addition, the X-ray crystal structure, along with the mutational studies, shows that Y100 is a key residue for the catalytic activity. Taken together, our results provide insights into the catalytic mechanism of <jats:italic>Pv</jats:italic> FKBP35-mediated <jats:italic>cis-trans</jats:italic> isomerization of substrate and ultimately might aid designing substrate mimetic inhibitors targeting the malarial parasite FKBPs. </jats:p>