Designer Ligands Specific for Kv1.3 Channels from a Scorpion Neurotoxin-Based Library

Venomous animals immobilize prey using protein toxins that act on ion channels and other targets of biological importance. Broad use of toxins for biomedical research, diagnosis and therapy has been limited by inadequate target discrimination, for example, among ion channel subtypes. Here, a synthetic toxin is produced by a new strategy to be specific for human Kv1.3 channels, critical regulators of immune T-cells. A phage-display library of 11,200 novel proteins is designed using the α-KTx scaffold found in 31 scorpion toxins that bind to potassium channels and mokatoxin-1 (moka1) isolated by sorting on purified target. Moka1 blocks Kv1.3 at nanomolar levels that do not impact Kv1.1, Kv1.2 or KCa1.1. Thus, moka1 suppresses CD3/28-induced cytokine secretion by T-cells without cross-reactive gastrointestinal hyperactivity. The 3D structure of moka1 rationalizes its specificity and validates the engineering approach revealing a unique interaction surface supported on an α-KTx scaffold. This scaffold-based/target-biased strategy overcomes many obstacles to production of selective toxins. Success with other toxin scaffolds and sorting with cell-surface targets has extended utility of the approach.