Two-dimensional 1H-NMR studies of phospholipase-A2-inhibitor complexes bound to a micellar lipid-water interface.

One- and two-dimensional NMR studies were performed on the complexes of porcine pancreatic phospholipase A2 with substrate analogs bound to a micellar lipid-water interface of fully deuterated dodecylphosphocholine. The interactions between the inhibitor and the enzyme were localized by comparison of the two-dimensional NOE spectra recorded for the enzyme-inhibitor complex using both protonated and selectively deuterated inhibitors. These experiments led us to the following conclusions for the phospholipase-A2-micelle complex: (i) the 38-kDa phospholipase A2 complex gives NMR spectra with relatively narrow lines, which is indicative of high mobility of the enzyme; (ii) the residues Ala1, Trp3, Phe63 and Tyr69 located in the interface recognition site, as well as Phe22, Tyr75, Phe106 and Tyr111 are involved in the micelle-binding process; (iii) when present on the micelle, phospholipase A2 is stereospecific for the inhibitor binding; (iv) the inhibitor, (R)-dodecyl-2-aminohexanol-1-phosphoglycol, binds stoichiometrically to phospholipase A2 with high affinity (Kd less than or equal to 10 microM); (v) the inhibitor binds in the active site of the enzyme, which is evidenced by large chemical-shift differences for Phe5, Ile9, Phe22, His48, Tyr52 and Phe106; (vi) the acyl chain of the inhibitor makes hydrophobic contacts (less than 0.4 nm) near Phe5, Ile9, Phe22 and Phe106. Comparison of our results on the enzyme-inhibitor-micelle ternary complex with the crystal structure of the enzyme-inhibitor complex [Thunnissen, M. M. G. M., AB, E., Kalk, K. H., Drenth, J., Dijkstra, B. W., Kuipers, O. P., Dijkman, R., de Haas, G. H. & Verheij, H. M. (1990) Nature 347, 689-691] shows that the mode of inhibitor binding is similar.