A Timely Structure: The physiology and behavior of most organisms are inextricably aligned with the day/night cycle. In mammals, these daily rhythms are generated by a circadian clock encoded by transcriptional activators and repressors operating in a feedback loop that takes about 24 hours to complete. A key participant in this loop is a heterodimeric transcriptional activator consisting of the CLOCK and BMAL1 proteins. Huang et al. (p. 189 , published online 31 May; see Perspective by Crane ) determined the crystal structure of a complex containing the PAS domains (implicated in protein-protein interactions) and the basic helix-loop-helix domains (implicated in DNA binding) from each protein. CLOCK and BMAL1 were observed to be tightly intertwined in an unusual asymmetric conformation, which may contribute to the stability and activity of the complex.

Significance: With-no-lysine (K) (WNK) protein kinases regulate ion transport. Mutations in WNKs 1 and 4 can cause a monogenic hypertension, pseudohypoaldosteronism type II (PHA2). The WNK-regulated protein kinases STE20/SPS1-related proline- and alanine-rich kinase (SPAK) and oxidative stress-responsive 1 (OSR1) mediate actions of WNKs on cation chloride cotransporters. The conserved C-terminal domains (CCTs) of OSR1/SPAK recognize linear R-F-x-V/I motifs in transporters and other protein targets. We discovered that OSR1/SPAK CCTs also recognize a motif variant, R-x-F-x-V/I, found in 8 of 16 inward rectifier K ⁺ (IRK) channels. We show that WNK and OSR1 regulate IRK channels, dependent on the presence of the variant motif. WNK kinase activity-dependent regulation of ion channels reveals a previously unknown mechanism and expands knowledge of potential WNK-OSR1/SPAK actions in cardiac and renal physiology.

The most frequent extracellular signal-regulated kinase 2 (ERK2) mutation occurring in cancers is E322K (E-K). ERK2 E-K reverses a buried charge in the ERK2 common docking (CD) site, a region that binds activators, inhibitors, and substrates. Little is known about the cellular consequences associated with this mutation, other than apparent increases in tumor resistance to pathway inhibitors. ERK2 E-K, like the mutation of the preceding aspartate (ERK2 D321N [D-N]) known as the sevenmaker mutation, causes increased activity in cells and evades inactivation by dual-specificity phosphatases. As opposed to findings in cancer cells, in developmental assays in Drosophila , only ERK2 D-N displays a significant gain of function, revealing mutation-specific phenotypes. The crystal structure of ERK2 D-N is indistinguishable from that of wild-type protein, yet this mutant displays increased thermal stability. In contrast, the crystal structure of ERK2 E-K reveals profound structural changes, including disorder in the CD site and exposure of the activation loop phosphorylation sites, which likely account for the decreased thermal stability of the protein. These contiguous mutations in the CD site of ERK2 are both required for docking interactions but lead to unpredictably different functional outcomes. Our results suggest that the CD site is in an energetically strained configuration, and this helps drive conformational changes at distal sites on ERK2 during docking interactions.