Identification of a novel Fe2+-chelating peptide from Pleurotus ostreatus: structural basis, chelation mechanisms, and transport pathways of the chelated Fe in Caco-2 cells.

Peptide‑iron chelates have garnered considerable attention as novel iron supplement. Our previous study successfully prepared iron-chelating peptides from Pleurotus ostreatus (IPPO). However, the amino acids sequence, structural basis for Fe2+ chelation of IPPO, and transport pathways of Fe2+ in peptide-Fe remain unclear. Therefore, IPPO was fractionated, purified and virtually screened to obtain peptides with the highest iron-chelating ability, and the structure-activity relationship of these peptides was elucidated. The chelation mechanisms between Fe2+ and DDSPWLPEHPE (DD11) were revealed, along with the potential transport pathways of the chelated Fe. The results showed that fraction F1-3 demonstrated the highest iron-chelating rate at 89.16 ± 0.85%, and 297 peptides were identified. Notably, 79.80% of these peptides had molecular weights below 2000 Da; peptides containing iron-chelating amino acids at the N- and C-termini constituted 5S3.50% and 66.70%, respectively; additionally, the proportion of iron-chelating amino acids exceeded 40% in 62.96% of the peptides. The optimal peptide DDSPWLPEHPE (DD11) exhibited an iron-chelating rate of 94.25 ± 0.76%. Its iron chelate (DD11-Fe) exhibited a porous sponge-like structure. Trp, Asp, Glu, Ser, and Leu within DD11 were crucial for iron chelation, and its β-sheet content increased significantly upon chelation. Iron coordinated with Asp1, Asp2, and Glu8 in DD11 maybe via a "monodentate + bidentate" mode. Furthermore, DD11-Fe significantly enhanced the bioavailability of Fe2+. Additionally, the findings indicate that both endocytosis and the paracellular pathway play pivotal roles in mediating the transepithelial transport of the DD11-Fe. These findings support the potential application of DD11-Fe as an innovative iron supplement. The impact of digestive enzymes, pH variations, and food matrices on its stability during gastrointestinal digestion warrants further investigation.