Interaction of phosphorylated tyrosine hydroxylase with 14‐3‐3 proteins: evidence for a phosphoserine 40‐dependent association

Tyrosine hydroxylase (TH) has been reported to require binding of 14‐3‐3 proteins for optimal activation by phosphorylation. We examined the effects of phosphorylation at Ser19, Ser31 and Ser40 of bovine TH and human TH isoforms on their binding to the 14‐3‐3 proteins BMH1/BMH2, as well as 14‐3‐3 ζ and a mixture of sheep brain 14‐3‐3 proteins. Phosphorylation of Ser31 did not result in 14‐3‐3 binding, however, phosphorylation of TH on Ser40 increased its affinity towards the yeast 14‐3‐3 isoforms BMH1/BMH2 and sheep brain 14‐3‐3, but not for 14‐3‐3 ζ. On phosphorylation of both Ser19 and Ser40, binding to the 14‐3‐3 ζ isoform also occurred, and the binding affinity to BMH1 and sheep brain 14‐3‐3 increased. Both phosphoserine‐specific antibodies directed against the 10 amino acids surrounding Ser19 or Ser40 of TH, and the phosphorylated peptides themselves, inhibited the association between phosphorylated TH and 14‐3‐3 proteins. This was also found when heparin was added, or after proteolytic removal of the N‐terminal 37 amino acids of Ser40‐phosphorylated TH. Binding of BMH1 to phosphorylated TH decreased the rate of dephosphorylation by protein phosphatase 2A, but no significant change in enzymatic activity was observed in the presence of BMH1. These findings further support a role for 14‐3‐3 proteins in the regulation of catecholamine biosynthesis and demonstrate isoform specificity for both TH and 14‐3‐3 proteins.