Study On Interaction Mechanism Of Antimicrobial Peptide CM15 With Phospholipid Membrane And Effect Of Ca²⁺ On The Hydration Shell Of DNA Duplex

Studying the phenomenon mechanism of biomolecules on the interface is the basis for understanding many activities of living substances.Through sum frequency generation vibrational spectroscopy（SFG-VS）technology and other characterization methods,we explained the mechanism of the interaction between the antimicrobial peptide CM15 and the negatively charged phospholipid bilayer under the influence of two different factors at the molecular level and revealed the role of the hydration layer surrounding the DNA double helix structure on the interface.Antimicrobial peptides have been proposed as an effective class of antimicrobial agents against microorganisms and their interaction with cell membrane can be affected by various internal and external factors.In this experiment,the interaction between a model antimicrobial peptide,CM15,and a negatively charged phospholipid bilayer,DPPG,was studied and two structurally-correlated characteristic variables,C-terminal amidation and temperature variation were introduced to reveal the interaction mechanism/efficiency.The results show that the C-terminal amidation can increase the positive charge of the peptides and provide a more rigid and stable structure,so that the antimicrobial peptides can be inserted into the bilayer to promote the adsorption to the bilayer surface and diruption of the outer layer,exhibiting less ordered insertion orientation.The temperature variables（from～20℃ to～35℃）mainly increases the fluidity of the bilayer to improve the penetration and insertion of the peptides,thereby enhancing the efficiency of antimicrobial peptides on the whole bilayer.This experimental study provides two practical cues to understand the disruption process of the negatively charged model biomembranes,which can lay the structural foundation for designing and developing high-efficiency antimicrobial peptides.Solvation of DNA in water facilitates the formation of a hydration layer surrounding it.The hydration layer can reflect the state of the DNA structure.The achiral and chiral SFG spectra were used to distinguish the interface water molecules and confirmed the presence of a chiral hydration layer in the DNA minor groove.Under a wide range of Ca²⁺concentration,the order of the achiral water molecules on the interface,including the achiral hydration layer surrounding the DNA duplex,will have an obvious concentration-dependent disruption.When the concentration of Ca²⁺is adjusted to the normal content in human serum,the chiral hydration layer will not change,which proves that the chiral hydration layer existing in the minor groove serves as a protective solvation shell to effectively protect the DNA duplex against the electric charge effect generated by Ca²⁺in the normal range.This study indicates the protective effect of the chiral hydration layer surrounding the DNA duplex,and also provides a verification method for the subsequent research on the interaction of other ions or substances with DNA.In summary,via SFG technology,from the perspective of micro molecular level,it was demonstrated that C-terminal amidation and temperature increase can effectively improve the transmembrane ability of CM15 peptides.And the chiral hydration layer in the DNA minor groove was proved its certain Ca²⁺charge resistance effect,which can protect and stabilize the structure of DNA duplex.The results have important scientific significance for understanding the biological interface.