Peptides that bound target proteins

With the help of NMR measurement, it has been shown that the Ca2+/calmodulin complex has a flexible structure. Flexibility is probably of great importance for the function of Ca2+/calmodulin. Structural information on Ca2+/calmodulin bound to substrates is only available for peptides derived from target proteins. In the complex with peptide substrates (Fig. 6.13), Ca2+/calmodulin has a collapsed structure in which the two globular domains are much closer together than in free Ca2+/calmodulin, and it wraps around and sequesters the helical calmodulin-binding peptides. 

Most one-bead-one-peptide libraries (see Section 4.3.7.3.1) are resin-bound and screened in direct solid-phase binding assays. In a typical binding assay, the library beads are incubated with the target protein labeled with a reporter molecule, such as an enzyme that catalyzes a reaction generating a colored compound, which in turn stains the beads to which the peptides that bind to the target protein are tethered. The positive (colored) beads are identified among the vast majority of noncolored beads, isolated, and submitted to structure determination of the peptides bound to them. 

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