Drosophila melanogaster NPC2 proteins bind bacterial cell wall components and may function in immune signal pathways

► Drosophila NPC2 proteins can be divided into three subgroups based on the numbers of cysteine residues. ► NPC2a, NPC2e and NPC2h, representing the three subgroups, are selected for further study. ► The three NPC2 proteins can bind to lipopolysaccharide, lipid A, peptidoglycan and lipoteichoic acid. ► Over-expression of NPC2a and NPC2e can stimulate diptericin promoter in S2 cells induced by peptidoglycan. ► NPC2 proteins may serve as co-receptors for different ligands to modulate immune signaling pathways.