1H, 13C, and 15N resonance assignment of the C terminal region of the disordered postsynaptic scaffold protein GKAP

Guanylate kinase-associated protein, GKAP, is a largely disordered scaffold protein with multiple interaction partners, playing a role in the organization of the postsynaptic protein network. Its C-terminus contains a binding motif for the PDZ domain of Shank proteins, another class of postsynaptic scaffolds. Based on predictions, this motif is preceded by a ~ 40-residue disordered segment with no known additional binding sites or established functional role. Here we report the expression, purification, and ¹H, ¹³C and ¹⁵N resonance assignment of the GKAP Ct43 construct containing the C-terminal 43 residues. This region is functionally intact, having a binding affinity to Shank1 PDZ in the micromolar range. Chemical shifts indicate that this region is indeed disordered but displays helical propensity in two regions. The short, slightly helical segment immediately before a PDZ-binding motif is somewhat comparable to the structural organization observed at the C-terminus of the E6 and RSK1 proteins, but its significance in GKAP is yet to be explored.