A combinatorial peptide library is a collection of fully or partially randomized peptides of defined length. Peptide libraries are classified either as synthetic (non-biological) or biological. As the name implies, synthetic libraries are produced through combinatorial peptide synthesis by allowing coupling of more than one amino acid residue per position. Here, individual peptides can be coupled to (and in fact synthesized on) beads in a one-bead-one-compound setting and screened against a fluorophore-labelled target using fluorescence-activated sorting. An alternative approach to synthetic library screening is positional scanning, where the peptide library is divided into sub-libraries, each having one of the positions defined (i.e., occupied by a specific amino acid residue), while the rest of the peptide structure is randomized. Each of the sub-libraries is assayed for activity to deduce the consensus peptide sequence with optimal activity. Conversely, in iterative deconvolution strategy optimal residues at individual positions are identified in a step-by-step fashion. Sub-libraries of randomized peptides but with different defined residues at first position are screened for activity, and the optimal residue in that position is retained in the second generation sub-library which contains peptides with different defined residues at the second position. This approach is repeated until all the positions have been interrogated.

Peptide Library Synthesis

Peptide Library is a large collection of synthetic peptides with a systematic combination of amino acids. These synthetic peptide library screening tools are used in epitope peptide mapping, peptide library screening for drug target validation and vaccine development. A typical peptide library contains a maximum of 25 amino acids. However, we can synthesize peptides of up to 30 amino acids in length in order to ensure that potential proteotypic peptides needed to be screened for an SRM assay are covered.

Peptide libraries are synthesized on our proprietary high throughput combinatorial peptide synthesis platform. Final unbound peptides are carefully placed in individual vials to avoid cross contamination or alternatively, packaged in a 96 well tube plate.

Our synthetic peptide libraries offer a flexible selection of peptide purity levels ranging from crude to 98% purity. Each random peptide in the library undergoes rigorous quality control to prevent any cross contaminants before delivery. All purified peptides are delivered with a QC reports of RP-HPLC, MS, and COA to ensure the highest quality.

What is a Peptide Library?

With the advent of combinatorial chemistry and the establishment of automated solid phase synthesis technologies, it became possible to synthesize large numbers of peptides in large quantities. These libraries are useful for the development of therapeutic drugs as well as for the design of peptide libraries to allow for screening of their activity using various combinations of screening technologies such as epitope mapping among others.

By combining different resins with linker molecules and coupling methods, a wide range of libraries can now be synthesized. After synthesis, libraries can be cleaved from the resin to yield peptide libraries in solution that can be used in various formats or for spotting onto supports such as membranes made of cellulose, pvdf or coated glass slides. Furthermore, peptide libraries can also be left on the resin or beads after synthesis. The use of a defined linker has proven to be beneficial for libraries on solid supports.

Applications of Peptide Library

Solid phase peptide synthesis has been successfully used to prepare libraries for the following applications:

• Antibody epitope mapping and validation to determine the specificity of antibodies
• Identification of bioactive peptides
• Development of biological assays
• T-cell epitope mapping
• Vaccine efficacy testing
• Screening for ligand-binding activities
• Screening for antimicrobial peptide activities
• Screening for peptide-protein interactions
• Libraries for drug discovery
• Libraries for affinity optimization
• Peptide libraries for LC-MS/MS method development and validation
• Libraries for receptor-ligand studies and cellular assays
• Libraries with constrained peptides
• Libraries containing peptides with modifications such as histone peptides
• Screening for MHC class I and class II peptides
• Many others

Type of Peptide Libraries

• On-resin or off-resin libraries
• Libraries containing scrambled amino acid residue peptides
• Peptide libraries containing specific linker molecules
• Dye-labeled peptide libraries
• Libraries with special modifications
• Polyepitope peptide library for vaccine development
• Other combinatorial libraries

Literature related to this subject indicates that synthetic peptide libraries can be used to identify biologically active peptides. For example, Smith et al. in 1994 used a random synthetic library of nonamer peptides to identify peptide motifs that bind to human class I major histocompatibility complex molecules HLA-A2 and B7. The identified allele-specific motifs for class I molecules were sequenced to identify the peptides that bound to the class I protein. These methods have the potential to detect peptides which may be valuable in predicting and engineering immunomodulatory T cell epitopes.

Peptide Pools contain a selection of peptides similar to a peptide library and are ideal for efficient in vitro stimulation of antigen-specific CD4+ and CD8+ T cells. If the pool contains 15-mer peptides with an 11 amino acid overlap, complete sequence of the respective antigen can be covered. This approach has been shown to be very effective in stimulating CD4+ as well as CD8+ T cells in various applications.

Peptide Arrays are similar to solid phase peptide libraries. Arrays of peptides may serve as valuable tools for identifying biologically active motifs as well as for profiling cellular activities, among other biological applications. Several methods for the preparation of peptide arrays have been reported. Arrays can be prepared by in situ peptide synthesis or by immobilization of functionalized peptides onto various supports.