Two-Dimensional Crystal Structures of Protein Kinase C-δ, Its Regulatory Domain, and the Enzyme Complexed with Myelin Basic Protein

AbstractTwo-dimensional crystals of protein kinase C (PKC) δ, its regulatory domain (RDδ), and the enzyme complexed with the substrate myelin basic protein have been grown on lipid monolayers composed of phosphatidylcholine: phosphatidylserine: diolein (45:50:5, molar ratio). Images have been reconstructed to 10-Å resolution. The unit cells of all three proteins have cell edges a=b and interedge angle γ=60o. RDδ has an edge length of 33±1Å, and its reconstruction is donut shaped. The three-dimensional reconstructions from the PKCδ C1b crystal structure (Zhang et al., 1995) can be accommodated in this two-dimensional projection. Intact PKCδ has an edge length of 46±1Å in the presence or absence of a nonhydrolyzable ATP analog, AMP-PnP. Its reconstruction has a similar donut shape, which can accommodate the C1b domain, but the spacing between donuts is greater than that in RDδ; some additional structure is visible between the donuts. The complex of PKCδ and myelin basic protein, with or without AMP-PnP, has an edge length of 43±1Å and a distinct structure. These results indicate that the C1 domains of RDδ are tightly packed in the plane of the membrane in the two-dimensional crystals, that there is a single molecule of PKCδ in the unit cell, and that its interaction with myelin basic protein induces a shift in conformation and/or packing of the enzyme