Solution Structure of the WNK1 Autoinhibitory Domain, a WNK-Specific PF2 Domain

WNK1 [with no lysine (K)-1] is a 250-kDa serine/threonine protein kinase involved in the maintenance of cellular salt levels and is directly linked to a hereditary form of hypertension. Here, we report the solution NMR structure of the autoinhibitory domain of WNK1 (WNK1-Al), a small regulatory subunit that lies immediately C-terminal of the kinase domain. We show that this domain is a homolog of the RFXV-binding PASK/FRAY homology 2 (PF2) domain found in OSR (oxidative stress responsive) and SPAK (serine/threonine proline-alanine-rich) kinases, which are substrates of WNK1. The WNK1-Al has a circularly permuted topology relative to the OSR1-PF2 domain. Nevertheless, like PF2 domains, WNK1-Al binds peptides that contain an RFXV motif with micromolar affinities as assessed by changes in H-1, N-15 heteronuclear single quantum coherence spectra. Mutations to the WNK1-Al and binding peptides confirm a similar binding mode. (C) 2013 Published by Elsevier Ltd.