SELF-ENCODED, HIGHLY CONDENSED SOLID PHASE-SUPPORTED PEPTIDE LIBRARY FOR IDENTIFICATION OF LIGAND-SPECIFIC PEPTIDES

The diversity of peptide libraries synthesized according to the ''mixi ng and portioning'' concept producing libraries containing one peptide per bead is limited by the number of beads. A method for the generati on and screening of peptide libraries with increased molecular diversi ty by synthesis of many peptides on each of the beads is described. Ac cording to this approach, in each synthesis cycle, every portion of th e beads gets a mixture of amino acids, thus the total number of peptid es is larger then the number of beads in the library. The degree of he terogeneity is increases from the N- to the C-terminal. Positions clos e to the N-terminal include relatively few amino acids, whereas positi ons closer to the C-terminal include a higher number of amino acids. T his structure allows generation of extensive diversity on each bead, w hile still retaining the ability to identify the peptide by N-terminal sequencing. The identification of the peptides on selected beads is a chieved by sequencing and by using a self-encoding system. This self-e ncoding system allows the use of coded as well as non-coded amino acid s which cannot be identified by automatic sequencers. According to thi s system, each non-coded amino acid is presented in a mixture with a c oded amino acid. The coded amino acid serves as an indicator for the p resence of the non-coded one. Only a portion of the target sequence is identified by N-terminal sequencing. Once partial sequence informatio n is obtained, secondary libraries are synthesized in order to find ou t which amino acids present in each position are responsible for bindi ng a ligand. The new approach enables generation and screening of up t o about 10(15) peptides per library, increasing the diversity of solid phase-screened peptides, or other non-sequenceable polymer libraries, by up to 10(7)-fold, thereby increasing the chances of discovering st ructures of interest.