pMag is a positively charged engineered domain that can heterodimerize with a compatible negatively charged 'nMag'-type domain upon stimulation with blue light. pMag is based on VVD, a small light-oxygen-voltage (LOV) domain-containing protein encoded by the Neurospora crassa Vivid gene (UniProtKB:Q9C3Y6). It lacks the N-terminal 36 residues (to increase stability of the protein) and contains the amino acid substitutions I52R and M55R relative to the wild-type sequence (PMID:25708714).