Abstract
Casein kinase 1 δ (CK1δ) is a regulatory enzyme in the mammalian circadian oscillator and represents a potential pharmacological target for modulating circadian rhythms. Crystal structures of four different polymorphs of CK1δ have previously been determined and this article reports the crystallization and structure determination of a new crystal form belonging to space group P21. Comparison of CK1δ crystal structures reveals few conformational differences within the C-terminal lobe, but more significant movements of the β-sheet region of the N-terminal lobe were observed.