Premium
Entropic allostery dominates the phosphorylation‐dependent regulation of Syk tyrosine kinase release from immunoreceptor tyrosine‐based activation motifs
Author(s) -
Feng Chao,
Roy Amitava,
Post Carol Beth
Publication year - 2018
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.3489
Subject(s) - syk , sh2 domain , immunoreceptor tyrosine based activation motif , allosteric regulation , chemistry , isothermal titration calorimetry , phosphorylation , biophysics , cooperative binding , tyrosine , biochemistry , plasma protein binding , binding site , tyrosine phosphorylation , stereochemistry , signal transduction , tyrosine kinase , receptor , biology
Abstract Spleen tyrosine kinase (Syk) is an essential player in immune signaling through its ability to couple multiple classes of membrane immunoreceptors to intracellular signaling pathways. Ligand binding leads to the recruitment of Syk to a phosphorylated cytoplasmic region of the receptors called ITAM. Syk binds to ITAM with high‐affinity (nanomolar K d ) via its tandem pair of SH2 domains. The affinity between Syk and ITAM is allosterically regulated by phosphorylation at Y130 in a linker connecting the tandem SH2 domains; when Y130 is phosphorylated, the binding affinity decreases (micromolar K d ). Previous equilibrium binding studies attribute the increase in the binding free energy to an intra‐molecular binding (isomerization) step of the tandem SH2 and ITAM, but a physical basis for the increased free energy is unknown. Here, we provide evidence that Y130 phosphorylation imposes an entropy penalty to isomerization, but surprisingly, has negligible effect on the SH2 binding interactions with ITAM and thus on the binding enthalpy. An analysis of NMR chemical shift differences characterized conformational effects of ITAM binding, and binding thermodynamics were measured from isothermal titration calorimetry. Together the data support a previously unknown mechanism for the basis of regulating protein–protein interactions through protein phosphorylation. The decreased affinity for Syk association with immune receptor ITAMs by Y130 phosphorylation is an allosteric mechanism driven by an increased entropy penalty, likely contributed by conformational disorder in the SH2–SH2 inter‐domain structure, while SH2‐ITAM binding contacts are not affected, and binding enthalpy is unchanged.