Abstract
The SAD/BRSK kinases participate in various important life processes, including neural development, cell cycle and energy metabolism. Like other members of the AMPK family, SAD contains an N-terminal kinase domain followed by the characteristic UBA and KA1 domains. Here we identify a unique autoinhibitory sequence (AIS) in SAD kinases, which exerts autoregulation in cooperation with UBA. Structural studies of mouse SAD-A revealed that UBA binds to the kinase domain in a distinct mode and, more importantly, AIS nestles specifically into the KD-UBA junction. The cooperative action of AIS and UBA results in an ‘αC-out' inactive kinase, which is conserved across species and essential for presynaptic vesicle clustering in C. elegans. In addition, the AIS, along with the KA1 domain, is indispensable for phospholipid binding. Taken together, these data suggest a model for synergistic autoinhibition and membrane activation of SAD kinases.
Highlights
The SAD/BRSK kinases participate in various important life processes, including neural development, cell cycle and energy metabolism
BRSK1/SAD-B and BRSK2/SAD-A are closely related to AMPK-a1/2 subunits and 10 other kinases (MARK1/2/3/4, SIK1/2/3, NUAK1/2 and MELK), and these kinases constitute a unique branch of the human kinome tree, the AMPK family[18]
To dissect the precise function of the non-catalytic region of SAD kinases, we examined the effects of step-wise C-terminal truncations of mouse SAD-A on enzyme activity (Fig. 1a and Supplementary Fig. 1)
Summary
The SAD/BRSK kinases participate in various important life processes, including neural development, cell cycle and energy metabolism. The AIS-KA1 fragment did not inhibit the activity of kinase domain alone, indicating that the AIS autoinhibition on SAD activity requires the UBA domain (Supplementary Fig. 5). We generated triple mutations to release both the UBA and AIS inhibitions, and these mutants yielded dramatic increase in the SAD activity, comparable to that of the kinase domain alone.
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