Self-assembled membranes offer a promising alternative for conventional membrane fabrication, especially in the field of ultrafiltration. Here, a new pore-making strategy is introduced involving stimuli responsive proteinpolymer conjugates self-assembled across a large surface area using dryingmediated interfacial self-assembly. The membrane is flexible and assembled on porous supports. The protein used is the cage protein ferritin and resides within the polymer matrix. Upon denaturation of ferritin, a pore is formed which intrinsically is determined by the size of the protein and how it resides in the matrix. Due to the self-assembly at interfaces, the membrane constitutes of only one layer resulting in a membrane thickness of 7 nm on average in the dry state. The membrane is stable up to at least 50 mbar transmembrane pressure, operating at a flux of about 21 000-25 000 L m(-2) h(-1) bar(-1) and displayed a preferred size selectivity of particles below 20 nm. This approach diversifies membrane technology generating a platform for "smart" self-assembled membranes.