A soluble recombinant hydroxyapatite-binding LL-37 fusion peptide shows efficient mineral adsorption and repair-associated bioactivity

Abstract LL-37 is a multifunctional human host-defense peptide, but its application is limited by membrane-associated toxicity, hemolysis, and challenges in recombinant production. Here, we engineered LL-37-HApBT by C-terminal fusion of LL-37 with a flexible linker and a hydroxyapatite-binding tag. LL-37-HApBT was recovered as a soluble recombinant peptide from Escherichia coli without a large protective carrier and purified by single-step affinity chromatography, yielding 2.75 mg L⁻¹. Sequence-based in silico analysis predicted a lower hydrophobic moment and a redistributed amphipathic profile for LL-37-HApBT compared with native LL-37, while the engineered construct remained strongly cationic. LL-37-HApBT adsorbed efficiently to hydroxyapatite, with an apparent adsorption capacity of 54.37 µg mg⁻¹ HAp and substantial adsorption present at 5 min. The peptide was cytocompatible with fibroblasts and endothelial cells and caused only 1.3% hemolysis at 30 µM (218 µg mL − 1 ). At nanogram-per-milliliter concentrations, LL-37-HApBT enhanced scratch wound closure in both cell types. Antibacterial activity was partial and more pronounced against Gram-negative bacteria, and concentration-dependent LPS interaction was observed. These findings support further evaluation of LL-37-HApBT as a bioactive hydroxyapatite-associating peptide for biomaterial applications.