Further Characterization of Galloyl Pedunculagin as an Effective Autophosphorylation Inhibitor of C-Kinase in Vitro

Abstract

The inhibitory effect of galloyl pedunculagin (GP) isolated from Platycarya strobilacea on the activity and autophosphorylation of Ca²⁺- and phospholipid-dependent protein kinase (C-kinase) was examined in vitro. It was found that (i) GP inhibited the activity (phosphorylation of complement C3 from guinea pig) of C-kinaseα (rat brain) in a dose-dependent manner with an ID₅₀ of approx. 0.12 μM; (ii) GP at lower doses (ID₅₀=approx. 6 nM) inhibited autophosphorylation of C-kinaseα; and (iii) the GP-induced inhibition of autophosphorylation of C-kinaseα and its enzyme activity was a manner non-competitive to ATP. Similar inhibitory effect of GP on autophosphorylation of recombinant human C-kinaseη (rhC-kinaseη) and its phosphorylating activity was observed. These results suggest that GP is an effective autophosphorylation inhibitor of these two C-kinase isoforms (α and η) in vitro. In addition, the CD analysis suggests that the proline-containing six amino acid residues (PVLTPP) including a threonine residue (autophosphorylation site) at the C-terminal region (positions 635—640) of C-kinaseα may be one of the GP-binding sites.