Peptide aptamer – CDK interactions. (a) Schematic diagram of STMpep9-CDK2 complex immobilized on a gold surface via conjugation between the SH group in a cysteine residue and the gold. (b) FRET analysis of STMpep2, STMpep9 and STM in solution on exposure to CDK2, CDK4 and CDK-free lysate. The peptide aptamers and lysate proteins were tagged with Alexa Fluor 488 and Alexa Fluor 555 fluorescent probes, respectively. The sample was excited at 488 nm and the resulting fluorescence from the Alexa Fluor 555 dye at 582 nm was measured. Yellow, strong interaction; dark yellow, medium interaction; black, no detectable interaction.