Considering these examples, the overall a-helical propensity of CD79a and CD79b is not unexpected. However, this tendency for a-helical structure indicated by the secondary chemical shifts does not exclude the presence of other secondary structure species in solution. Since the presence of helical and b/extended structures have opposite effects on observed secondary chemical shifts, the only definite conclusion that can be drawn from our secondary chemical shift data is that, in solution, the residual helical structure has higher occupancy in comparison to the alternative conformations. Neither can we rule out the possibility of onset of non-helical structures in CD79a and CD79b upon interactions with their binding partners. It has previously been demonstrated that upon interaction with SH2 domains, ITAM residues in the vicinity of the phosphorylated tyrosines adopt an extended structure. As mentioned, it is common for IDPs to have several functional conformations and adjust their structure to specific binding partners via conformational selection or coupled folding and binding. In the following paragraphs we focus on the effect of phosphorylation on the observed helical propensity of CD79a and CD79b. In vivo the ITAMs located in the cytoplasmic domains of CD79a and CD79b are phosphorylated by members of the Src-family kinases and the SYK kinase. In this study we used a recombinant version of the Src-family member Fyn to perform in vitro phosphorylation of 15N/13C labeled samples of CD79a and CD79b. As has been previously noted and was also observed in this study, the BATCP aromatic side-chain 1H-13C resonances of solvent exposed protein tyrosine residues show very limited chemical shift dispersion making direct ABT-418 hydrochloride determination of multiple phosphorylation states difficult. Instead, identification of phosphotyrosine positions was performed by examining backbone chemical shift changes displayed by residues surrounding the expected phosphorylation sites. The differences in chemical shifts between the non-phosphorylated and the phosphorylated states of CD79a and CD79b are here defined as d2dP where d and dP are the chemical shifts in the non-phosphorylated and phosphorylated states respectively. If an expected phosphorylation site has a neighboring residue stretch with d2dP values that deviate significantly from zero, this means that the site may have become phosphorylated.