Influence of the headgroup structure on the GST-PI3Kγ affinity to PtdIns and PtdIns(4,5)P2 monolayers. (A) IRRA spectra of DPPtdIns (dotted line) and DPPtdIns(4,5)P2 (solid line) and (B) IRRA spectra of DOPtdIns (dotted line) and DOPtdIns(4,5)P2 (solid line), with adsorbed GST-PI3Kγ on Tris buffer at 20 mN/m and acquired with p-polarized light at 40° angle of incidence. The kinase was injected at 5 mN/m. After protein adsorption, the film was compressed to 20 mN/m.