Glutaminase-catalyzed γ-glutamylation to produce CCK secretion-stimulatory γ-[Glu]n-Trp peptides superior to tryptophan

Abstract

This study follows recent attempts to discover and improve the effectiveness of dietary peptides as stimulators of cholecystokinin (CCK) secretion. This study is the first report about the effect of γ-[Glu](n=1,2,3,4)-Trp, produced via γ-glutamylation by glutaminase, on CCK release and Ca2+-sensing receptor (CaS) activation. All these Trp-containing γ-glutamyl peptides exhibited abilities to trigger CCK secretion at 2.5–10 mM, with the highest amount of CCK (187.19 ± 0.68 pg/mL) occurring at 10 mM of γ-Glu-Trp and 5 mM of [Ca2+]e. A CaSR-mediated Ca2+/CaM/CaMK pathway in γ-[Glu](n=0,1,2,3,4)-Trp-induced CCK secretion was proposed based on the following results: the exposure to γ-Glu-Trp increased the protein expression level (Western bolt analysis); The intracellular calcium ([Ca2+]i) mobilization in response to γ-[Glu](n=0,1,2,3,4)-Trp was strongly enhanced; The inhibitors of signaling pathway proteins (NPS-2143, BAPTA-AM and KN62) abolished partially γ-[Glu](n=1,2,3,4)-Trp-induced CCK secretion. Glutaminase-catalyzed γ-glutamylation might be a useful approach for producing superior CCK secretion peptide stimulators.

Keywords

• γ-[Glu](n=0,1,2,3,4)-Trp
• Cholecystokinin
• In vitro
• CaSR
• Western blotting