The mechanism of phosphatidylcholine-induced interference of PAP (248-286) aggregation

Seminal amyloids are well known for their role in enhancing HIV infection. Among all the amyloidogenic peptides identified in human semen, PAP_248-286 was found to be the most active and was termed as semen-derived enhancer of viral infection (SEVI). Although amyloidogenic nature of the peptide is mainly linked with enhancement of the viral infection, the most active physiological conformation of the aggregated peptide remains inconclusive. Lipids are known to modulate aggregation pathway of a variety of proteins and peptides and constitute one of the most abundant biomolecules in human semen. PAP_248-286 significantly differs from the other known amyloidogenic peptides, including Aβ and IAPP, in terms of critical concentration, surface charge, fibril morphology, and structural transition during aggregation. Hence, in the present study, we aimed to assess the effect of a lipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), on PAP_248-286 aggregation and the consequent conformational outcomes. Our initial observation suggested that the presence of the lipid considerably influenced the aggregation of PAP_248-286 . Further, ZDOCK and MD simulation studies of peptide multimerization have suggested that the hydrophobic residues at C-terminus are crucial for PAP_248-286 aggregation and are anticipated to be major DOPC-interacting partners. Therefore, we further assessed the aggregation behaviour of C-terminal (PAP_273-286 ) fragment of PAP_248-286 and observed that DOPC possesses the ability to interfere with the aggregation behaviour of both the peptides used in the current study. Mechanistically, we propose that the presence of DOPC causes considerable inhibition of the peptide aggregation by interfering with the peptide's disordered state to β-sheet transition.