Extracellular secretion is a beneficial way to produce recombinant proteins at an industrial scale. Among bacterial secretion systems, the type 1 secretion system (T1SS) in Gram-negative bacteria is particularly attractive due to its simple architecture involving only three proteins and one-step translocation across both inner and outer membranes. However, proteins that fold rapidly within the cell often fail to pass through the narrow T1SS channel tunnel, limiting its industrial application. To address this limitation, we engineered a 10-amino-acid calcium-binding sequence (CBS) that disrupts proximal secondary structures through electrostatic repulsion at low Ca