Red-light induced aggregation of phytochrome 1 decorated E2 protein nanocage

Abstract

Affinity precipitation can be used to purify target protein by averting from chromatographic operation. One strategy for inducing precipitation after capturing target protein is to use elastin-like polypeptide (ELP) for affinity precipitation, wherein affinity ligands are fused with ELP chains. After binding between target protein and affinity ligand, precipitation is achieved by reaching transition temperature. However, this method is ineffective due to the requirement of salt addition to lower the transition temperature, a procedure that could potentially damage the target protein. ☐ Here, we investigated a benign environmental trigger that minimized protein damage and achieved precipitation using red light responsive cyanobacteria phytochrome 1. By conjugating multiple phytochrome 1 onto a larger protein scaffold, we created a large protein complex that could crosslink due to its multivalent nature and form precipitate only in the presence of red light in the environment. Moreover, we demonstrated the cyclic reversibility of phytochrome 1 and thus the red light induced precipitate can be dissociated into individual nanocages.