Conjunctive gates in engineered proteins: a review of mechanisms and boundary cases

The Protein Engineering Grammar describes proteins whose function is gated by a controlled input, using four terms: Sensor, Gate, Processor, and Actuator. Two Gate values require conjunction of inputs, which this review calls conjunctive gates: AND-like, requiring multiple inputs together, and Conditional Unlock, in which a single input switches on a function that is off by default. The review examines their molecular implementation and the specificity achieved across modalities (therapeutics, synthetic biology, de novo design, and biomaterials), classifies reusable trigger-recognition tactics, and discusses the role of computational and AI-based design platforms.