Webinar Snapshots: Sequence-Specific “Peptoids” for Antifouling, Antibacterial and Self-Assembly Applications

Presented by K.H Aaron Lau, PhD, Senior Lecturer (Associate Professor) at the Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, Scotland, United Kingdom

Analogous to peptides, non-natural poly(N-substituted glycine) “peptoids” exhibit self-assembly properties and bioactivity that are encoded by the ordering of monomer residues into specific sequences along their polymer backbone. Peptoids differ from peptides in the shift of the sidechain attachment to the backbone amide-nitrogen atoms. They are resistant to protease degradation and have simplified intermolecular interactions.

In this webinar, sponsored in partnership with Xtalks K.H Aron Lau highlights recent efforts in exploring solid-phase synthesized peptoids for applications beyond their conventional use in combinatorial drug discovery. This includes a look into how peptoids can be tailored to form antifouling peptoid polymer brushes and antibacterial surfaces, and also self-assembly. The webinar concludes with a presentation of the finer points of peptoid synthesis using Prelude® X peptide synthesizer.

Sequence-specific polymers such as peptoids are a basis for bioinspired materials

In biology, most activities occur at interfaces. The cell interacts with its environment at the nanoscale and the cell membrane can be regarded as a nanostructure (3 nm thick) that helps in determining the flow of materials in and out of the cell, where membrane proteins can move, functions as an interface to the extracellular matrix and other cells etc. The sequence-specific polymers (peptides) involved in these processes and interactions inspire the design of biomaterials with specific structure and function.

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Peptoid structure and properties

Peptoids are a simplified mimic of natural peptides and are therefore favored for creating structure and function. They are relatively easy to synthesize by sub-monomer solid-phase synthesis. A peptide and an alpha peptide differ by a one-atom shift of the side-chain that changes chemistry. Peptoids have simplified hydrogen-bonding and are more modular, enabling more focus on side-chain functionality and simpler synthesis. A particular benefit is that they are not recognized by proteases.

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Sub-monomer solid phase protocol

Peptoids can be synthesized by a sub-monomer solid-phase protocol and a wide range of sidechains are available that enable tailored synthesis at low cost. The lab builds peptoids from the ground up, based on existing sequences and using Prelude X peptide synthesizer, which is very suitable for peptoid chemistry. Knowledge of surface chemistry and characterization is very important in this process.

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Antifouling peptoid polymer brushes

The easiest way to graft or bind onto a surface is to produce a grafted brush, which can prevent protein adsorption and cell attachment. The aim is to create better polymer brushes able to resist the non-specific attachment of biomolecules to surfaces. For example, in nano-medicine, one problem is that polymers can be recognized by the immune system or are adsorbed away from the intended site. Another challenge is to prevent bacteria from infecting a wound site or attaching close to a biomedical device. Peptoids can be used to develop brushes and work well in this application.

 

 

A homo-polypeptoid with an anchor group was developed and highly sensitive single molecule fluorescence microscopy showed that it was better than PEG at reducing protein adsorption, and the use of atomic force microscopy (AFM) to count molecules indicated a 10-fold improvement over PEG.

Precise charge placement and separation using spaced charged groups can be used to control electrostatic interaction with proteins. The brushes can suppress bacterial adhesion but not at the level of 5-logs needed. This required another approach.

 

 

 

 

The group looked at the design of antibacterial surfaces that would help limit the environmental release of toxic antimicrobials. This requires immobilizing a sequence on the surface of, for example, a biomedical device to generate an antimicrobial surface.

They immobilized a chemically linked antibacterial sequence to a surface and found that including a long linker gives an antimicrobial effect, highlighting the importance of engineering a surface to achieve the desired effect.

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Peptoids give insight into protein secondary structure

Protein mimicry is the holy grail for polymer science and peptoids can help in the understanding of the secondary structure of proteins and there are many structures known (e.g. ribbons and sheets).

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Self-assembly

Self-assembly of peptoids is less well-known, especially for short sequences. Key findings included:

  • Dipeptoids can form crystals and they can pi-stack and also form chain-end hydrogen-bonding networks.

  • Trimers can form nanofibers that are quite soluble and flexible.

  • Adding ionizable groups and a hydrophobic tail enables the formation of ultra-small micelles with sequence-sensitivity that might enable the control of self-assembly.

  • Peptoid nanosheets can form a molecular scaffold that interact with stem cells in a compatible way and may stimulate metabolism.

 

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Peptoid synthesis using Prelude X peptide synthesizer

Peptoids are built from building blocks on resin in an iterative cycle to create a sequence-specific chain. DIC (N,N′-Diisopropylcarbodiimide), a simple coupling reagent is used. The main chain is achiral and side chains are added as an amine. The process is fast and simple, with no protection/deprotection.

One cycle at room temperature can run efficiently under 1h, faster at higher temperatures. Reagents are at high concentration.

Prelude X peptide synthesizer has been used to synthesize a range of known sequences and modifications to meet application needs, including:

  • Antimicrobial set
  • 20-mer nanosheet sequence
  • 36-mer nanosheet sequence

Details of the protocol used on Prelude X are described.

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To find out more about applications for peptoids and how they can be synthesized, view the webinar:

Sequence-Specific Peptoids for Antifouling, Antibacterial and Self-Assembly Applications

View the webinar

 

 

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