Monitoring Antimicrobial Mechanisms of Surface-Immobilized Peptides in Situ

Abstract

Antimicrobial peptides (AMPs) in free solution can kill bacteria by disrupting bacterial cell membranes. Their modes of action have been extensively studied, and various models ranging from pore formation to carpet-like mechanisms were proposed. Surface-immobilized AMPs have been used as coatings to kill bacteria and as sensors to capture bacteria, but the interaction mechanisms of surface-immobilized AMPs and bacteria are not fully understood. In this research, an analytical platform, sum frequency generation (SFG) microscope, which is composed of an SFG vibrational spectrometer and a fluorescence microscope, was used to probe molecular interactions between surface-immobilized AMPs and bacteria in situ in real time at the solid/liquid interface. SFG probed the molecular structure of surface-immobilized AMPs while interacting with bacteria, and fluorescence images of dead bacteria were monitored as a function of time during the peptide-bacteria interaction. It was believed that upon bacteria contact, the surface-immobilized peptides changed their orientation and killed bacteria. This research demonstrated that the SFG microscope platform can examine the structure and function (bacterial killing) at the same time in the same sample environment, providing in-depth understanding on the structure-activity relationships of surface-immobilized AMPs.

Structure and Dynamics of Interfacial Peptides and Proteins from Vibrational Sum-Frequency Generation Spectroscopy

“…The antibacterial activity of the peptides was associated with the change of their orientation upon interaction with bacteria, i.e., the bacterium-induced peptide bending inflicts damage to the bacteria. 304 This behavior differs from the surface-immobilized behavior of the cecropin P1 peptide (see section 3.2.2).…”

AMP–Chitosan Coating with Bactericidal Activity in the Presence of Human Plasma Proteins

“…Costa et al and Barbosa et al showed the importance of peptide attachment site in covalent immobilization on antimicrobial activity [14,15,22]. hLF (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and Dhvar-5 possess a head-to-tail amphipathicity that probably promotes distinctive interactions with bacteria. In this work, we showed that the antimicrobial activity of the α-helical MSI-78(4-20) peptide was not affected by attachment site upon immobilization onto chitosan films, probably due to the distribution of the hydrophobic and hydrophilic amino acids along the sequence.…”

“…However, AMPs’ activity may be influenced by several factors, such as solid supports, spacer specificities, surface density, exposure, orientation, and peptide stability [ 4 ]. Several α-helical AMPs have already been immobilized on different surfaces using a variety of conditions, and results show that their efficacy may depend on the terminus chosen to tether the peptide to the surface, as this may lead to exposure of termini with different characteristics or induce different AMP conformations and orientation on the surface [ 10 , 11 , 12 , 13 ]. MSI-78, the parent peptide, was previously immobilized on alkyne-terminated self-assembled monolayers through both its C - and N - termini.…”

Defensin-Like Peptides and Their Antimicrobial Activity in Free-Form and Immobilized on Material Surfaces

“…However, as shown in Figure 7, the orientation of AMPs changes after their initial interaction with bacteria (i.e., the immobilized α-helices bind to the anionic lipid bilayer). Since immobilized AMPs cannot follow the barrel-stave or toroidal model due to limited mobility, it is suggested that the charge-charge interaction plays a dominant role in the elimination of bacteria [104,105]. Additionally, when functionalizing the material's surface with different reactive groups as seen in Figure 8, the orientation of immobilized AMPs can be controlled using chemo-selective (i.e., directed immobilization) coupling reactions.…”