1H, 13C, 15N resonance assignment of recombinant Euplotes raikovi protein Er-23.

Er-23 is a small, 51 amino acid, disulfide-rich pheromone protein used for cell signaling by Euplotes raikovi. Ten of the 51 amino acids are cysteine, allowing up to five disulfide bonds. Previous NMR work with Er-23 utilized homologously expressed protein, prohibiting isotopic labeling, and consequently the chemical shift assignments were incomplete. We have expressed uniformly 15N and 13C-labeled Er-23 in an E. coli expression system. Here we report the full backbone and side chain resonance assignments for recombinant Er-23.