One-step purification of a bioactive PAK1-derived peptide

The serine/threonine kinase PAK1 serves as a mediator of cytoskeletal reorganization and cancer-related signaling downstream of the small GTPases. Due to the challenges in purifying PAK1 complexes, a 46-residue peptide from PAK1, is widely used to study PAK1-Cdc42 signaling. Traditionally, this purification involved multi-step chromatography of recombinant GST-PBD46 complexes, yielding approximately 1 mg per 1.5 L culture. In this study, a 30 min heat treatment step after thrombin cleavage was used to precipitate GST while leaving pure PBD46 in solution. This step eliminated the need for further affinity and size-exclusion chromatography steps. This improved protocol produces proteins with a 6.5-fold higher yield, halves the purification processing time, and produces peptides with ≥95 % purity. Mass spectrometry, CD, fluorescence, and ¹H-¹⁵N HSQC NMR confirmed the heat-purified PBD46's identity, structure, folding, and binding to Cdc42. The method also successfully separated other small peptides (e.g., ACK1) but not larger folded proteins. This rapid and scalable approach facilitates peptide production and biochemical studies without compromising the structural or functional integrity. We believe that the method described herein is applicable to other stable GST-fused recombinant proteins.