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Eukaryotic cyclophilin as a molecular switch for effector activation
Author(s) -
Coaker Gitta,
Zhu George,
Ding Zhaofeng,
Van Doren Steven R.,
Staskawicz Brian
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05335.x
Subject(s) - effector , biology , pseudomonas syringae , peptidylprolyl isomerase , cyclophilin , cis trans isomerases , arabidopsis , biochemistry , microbiology and biotechnology , isomerase , mutant , enzyme , gene
Summary Gram‐negative phytopathogenic bacteria, such as Pseudomonas syringae , deliver multiple effector proteins into plant cells during infection. It is hypothesized that certain plant and mammalian effector proteins need to traverse the type III secretion system unfolded and are delivered into host cells as inactive enzymes. We have previously identified cyclophilin as the Arabidopsis eukaryotic activator of AvrRpt2, a P. syringae effector that is a cysteine protease. Cyclophilins are general folding catalysts and possess peptidyl‐prolyl cis/trans isomerase (PPIase) activity. In this paper, we demonstrate the mechanism of AvrRpt2 activation by the Arabidopsis cyclophilin ROC1. ROC1 mutants lacking PPIase enzymatic activity were unable to activate AvrRpt2. Furthermore, nuclear magnetic resonance spectroscopy revealed a structural change in AvrRpt2 from an unfolded to a folded state in the presence of ROC1. Using in vitro binding assays, ROC1's consensus binding sequence was identified as GPxL, a motif present at four sites within AvrRpt2. The GPxL motifs are located in close proximity to AvrRpt2's catalytic triad and are required for protease activity both in vitro and in planta . These data suggest that after delivery into the plant cell during infection, cyclophilin binds AvrRpt2 at four sites and properly folds the effector protein by peptidyl‐prolyl cis/trans isomerization.