It was proposed previously that the FHA2 domain of the @entity375 protein kinase @entity16387 has dual specificity toward pY and pT peptides. The consensus sequences of pY peptides for binding to FHA2, as well as the solution structures of free FHA2 and FHA2 complex with a pY peptide derived from @entity20087 , have been obtained previously. We now report the use of a pT library to screen for binding of pT peptides with the FHA2 domain. The results show that FHA2 binds favorably to pT peptides with Ile at the +3 position. We then searched the @entity20087 sequences with a pTXXI/L motif, and tested the binding affinity of FHA2 toward ten pT peptides derived from @entity20087 . One of the peptides, (599)EVEL(pT)QELP(607), displayed the best binding affinity (K(d)=12.9 microM) and the greatest chemical shift changes. The structure of the FHA2 complex with this peptide was then determined by solution NMR and the structure of the complex between FHA2 and the pY peptide (826)EDI(pY)YLD(832) was further refined. Structural comparison of these two complexes indicates that the Leu residue at the +3 position in the pT peptide and that at the +2 position in the pY peptide occupy a very similar position relative to the binding site residues from FHA2. This can explain why FHA2 is able to bind both pT and pY peptides. This position change from +3 to +2 could be the consequence of the size difference between Thr and Tyr. Further insight into the structural basis of ligand specificity of FHA domains was obtained by comparing the structures of the FHA2-pTXXL complex obtained in this work and the FHA1-pTXXD complex reported in the accompanying paper.

Solution structure of the @entity375 XXXX FHA2 complexed with a phosphothreonine peptide pTXXL: comparison with the structures of FHA2-pYXL and FHA1-pTXXD complexes.

@entity20087 :: ('851803(Tax:4932)', 'Gene') :: ['Rad9'] @entity375 :: ('4932', 'Species') :: ['yeast'] @entity16387 :: ('855950(Tax:4932)', 'Gene') :: ['Rad53']
@entity16387 :: (855950(Tax:4932),Gene) :: ['Rad53']
