Molecular Determinants of a Regulatory Prolyl Isomerization
in the Signal Adapter Protein c‑CrkII
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Abstract
The cellular CT10 regulator of kinase
protein (c-CrkII) transmits
signals from oncogenic tyrosine kinases to cellular targets. Nuclear
magnetic resonance studies had suggested that in chicken c-CrkII a
native state prolyl <i>cis</i>–<i>trans</i> isomerization is involved in signal propagation. Corresponding evidence
for the closely related human c-CrkII was not obtained. Here we analyzed
the kinetics of folding and substrate binding of the two homologues
and found that <i>cis</i>–<i>trans</i> isomerization
of Pro238 determines target binding in chicken but not in human c-CrkII.
A reciprocal mutational analysis uncovered residues that determine
the isomeric state at Pro238 and transmit it to the binding site for
downstream target proteins. The transfer of these key residues to
human c-CrkII established a regulatory proline switch in this protein,
as well. We suggest that Pro238 isomerization extends the lifetime
of the signaling-active state of c-CrkII and thereby functions as
a long-term molecular storage device