Complexation of Walnut Protein with Adenosine Nucleotides: Effects on Protein Functionality and Novel Insight into the Absorption Mechanism of cAMP

Adenosine nucleotides are vital bioactive molecules with potential applications in functional foods and clinical nutrition; however, their poor membrane permeability limits their bioavailability. The utilization of plant proteins is often hindered by their poor solubility and digestibility. To address these challenges, we developed a strategy involving the formation of complexes between the walnut protein (WP) and four adenosine nucleotides. Spectroscopy, mass spectrometry, cell model, molecular docking, and other experimental techniques were conducted in this study; these methods demonstrated that such a complexation significantly enhanced the solubility of the WP to 3~4 mg/mL, while also enhancing its digestive stability in the gastrointestinal tract by 2~3-fold. Most notably, while all adenosines interacted with the protein matrix, cAMP exhibited a superior absorption efficiency, around 100-fold compared with its linear counterparts. Mass spectrometry and molecular docking were combined to reveal a new absorption mechanism for cAMP with the WP hydrolysate. These findings suggest that the complexation of WP and adenosine nucleotides offers a platform to overcome plant protein limitations and achieve efficient intracellular adenosine delivery, thereby establishing a foundation for its use in the development of functional foods.