Peptide combinatorial library positional scanning

Dooley, C., Houghten, R. (1993) The use of positional scanning synthetic peptide combinatorial libraries for the rapid determination of opioid receptor ligands. Life Sci 52, 1509-1517. 

For heterocychc libraries in a positional scan format, a key factor is in being able to devise a method for efficiendy carrying out the construction of the library in the positional scan format. For peptide hbraries, the Houghten laboratory was able to employ mixtures of building blocks where the molar ratios had been adjusted to account for reactivity (kinetic rate) differences of incoming building blocks and thereby achieve equimolar mixtures. A non-peptide, two-dimensional positional scan library, identified as an indexed combinatorial library, was reported recently [63], In this work a novel acetyl-... 

Pinilla C, Appel JR, Houghten RA, Positional scanning synthetic peptide combinatorial libraries, In Schneider CH, Eberle AN eds., Peptides 1992, ESCOM, Leiden, 1993, p. 65-66. 

Pinilla C, Appel JR, Blanc P, Houghten RA. Rapid identification of high affinity peptide ligands using positional scanning synthetic peptide combinatorial libraries. Bio Techniques. 1992 13 901-902,... 

Identification of High Affinity Peptide Ligands Using Positional Scanning Synthetic Peptide Combinatorial Libraries. 

Because of their ease of synthesis and their structural similarity to peptides, many laboratories have used peptoids as the basis for combinatorial drug discovery. Peptoids were among the first non-natural compounds used to establish the basic principles and practical methods of combinatorial discovery [17]. Typically, diverse libraries of relatively short peptoids (< 10 residues) are synthesized by the mix-and-split method and then screened for biological activity. Individual active compounds can then be identified by iterative re-synthesis, sequencing of compounds on individual beads, or indirect deduction by the preparation of positional scanning libraries. 

A special application of the peptide scan is the hybritope scan (hybrid-epitope) (44,45). In order to increase the affinity by extention of the peptide sequence in a hybritope scan, several mixtures of amino acids at positions flanking the related sequence of the protein are introduced. Another strategy to optimize a peptide scan is the so-called duotope scan (duo-epitope) (46). For a duotope scan one generates the peptide scan twice and combines the sequence of both arrays linked via a spacer, such as two -alanine molecules. In this way it is possible to avoid possible steric hindrance and to increase activity by extention of the active sequence. The pattern of such a duotope scan resembles that of a combinatorial library with the exception that each field represents a combination of two sequences rather than two amino acids. 

A special type of combinatorial library is the positional scanning library (43, 49,58). This array contains a set of combinatorial libraries with one or more (two positions = dual positional scan (4, 59))deconvoluted positions. In each of the synthesized libraries the deconvoluted positions are different. After screening one can combine the positions of the spot with the peptides of highest activity of each library to obtain the complete sequence of a peptide with most likely the greatest activity. 

Peptides and Peptidomimetics from Combinatorial Libraries. Mixture-based combinatorial peptide libraries have been extensively explored by Houghten and coworkers and have led to the identification of a variety of peptides with affinity for opioid receptors (see Ref 946 for a review). Early hexapeptide libraries, deconvoluted by binding to p opioid receptors and either iterative deconvolution (947)or positional scanning (948 see Ref 946 for a description of these deconvolution techniques), identified sequences related to the enkephalins. Other nonacetylated peptide libraries have identified more varied peptides, some that resemble opioid peptides and some that do not. Iterative deconvolution of a hexapeptide library resulted in identification of both Tyr-Pro-Phe-Gly-Phe-XNH, (X = one of 20 natural amino acids), reminiscent of the... 

A positional scanning combinatorial library (Fig. 3) can be used in place of iterative synthesis and screening [9]. In this approach, all library mixtures are synthesized and assayed for activity. The most active mixture from each positional library reveals the preferred residue at each position. Because all possible combinations of residues are represented in one of the sublibraries, the approach should be insensitive to synergistic effects associated with the structure. The orthogonal combinatorial library consists of two different libraries made up of the same compounds and synthesized in a way that mixtures from each library will only share one peptide or subunit [10]. In this way, these libraries are nonoverlapping, or orthogonal. 

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