Initial three-dimensional reconstructions of protein kinase C δ from two-dimensional crystals on lipid monolayers

Two-dimensional crystals of protein kinase C δ (PKCδ) and of its regulatory domain (RDδ) were grown on lipid monolayers and analyzed by electron microscopy at tilt angles varying from − 50° to + 55°. Although the crystals exhibit pseudo-3-fold symmetry, analysis of difference phase residuals indicates that there is only one way to align the crystals for merging so the data were processed in plane group P1. Three-dimensional reconstructions generated for several two-dimensional crystals each of PKCδ and RDδ show good agreement and are consistent with membrane attachment via a single C1 subdomain, a small surface contact by one or two loops from the C2 domain, and, in intact PKCδ, a small appendage from the catalytic domain, probably V5. Two-dimensional crystallography with three-dimensional reconstruction should be suitable for examination of additional PKC isozymes and for analysis of the enzymes bound to substrates and other proteins.