Microcrystals of the beta 1 isoenzyme of protein kinase C: an electron microscopic study

Microcrystals of protein kinase C beta 1 have been grown from solutions of poly(ethylene glycol). Image analysis of electron micrographs of the protein crystals, which diffracted to 5.0 nm, revealed p3 symmetry with a unit cell of about 10.3 nm x 10.3 nm. The electron stain-excluding densities showed a three-domain ring structure in projection, giving kidney bean-shaped molecules of about 7.0 nm x 4.5 nm diameter, packed as trimers. The implications of these observations for the function of the enzyme are discussed.