HT1 and HT1(A109V) Phosphorylate the SLAC1 N Terminus and GHR1.
MPK12 and MPK4 inhibit the phosphorylation of GHR1 by HT1(A109V) less than the phosphorylation of GHR1 by HT1. Autoradiographs and Coomassie Brilliant Blue G 250 staining are shown in (A) to (D).
(A) HT1 and HT1(A109V) phosphorylate GHR1 and SLAC1 N terminus but not OST1(K50N) or SLAC1 C terminus in tested conditions.
(B) HT1-induced autophosphorylation and phosphorylation of GHR1 are inhibited by MPK12, and the inhibition is decreased in HT1(A109V).
(C) MPK4, MPK4(D198G/E202A), and kinase-inactive MPK4(K72M/K73R) do not phosphorylate kinase-inactive HT1(K113M).
(D) MPK4 and MPK4(K72M/K73R) inhibit HT1-induced phosphorylation of GHR1, and the inhibition is decreased in HT1(A109V). MPK4(D198G/E202A) inhibits HT1 activity less than MPK4 and MPK4(K72M/K73R). MPK4, MPK4(D198G/E202A), and MPK4(K72M/K73R) do not phosphorylate GHR1.