Applications of microbial transglutaminase (mTGase) produced fromStreptomyces mobarensis(S. mobarensis) were recently extended from food to pharmaceutical industry. To use mTGase for clinical applications, like generation of site specific antibody drug conjugates, it would be beneficial to manufacture mTGase inEscherichia coli(E. coli). To date, attempts to express recombinant soluble and activeS. mobarensismTGase have been largely unsuccessful. mTGase fromS. mobarensisis naturally expressed as proenzyme and stepwise proteolytically processed into its active mature form outside of the bacterial cell. The pro-domain is essential for correct folding of mTGase as well as for inhibiting activity of mTGase inside the cell. Here, we report a genetically modified mTGase that has full activity and can be expressed at high yields in the cytoplasm ofE. coli. To achieve this we performed an alanine-scan of the mTGase pro-domain and identified mutants that maintain its chaperone function but destabilize the cleaved pro-domain/mTGase interaction in a temperature dependent fashion. This allows proper folding of mTGase and keeps the enzyme inactive during expression at 20°C, but results in full activity when shifted to 37°C due to loosen domain interactions. The insertion of the 3C protease cleavage site together with pro-domain alanine mutants Tyr14, Ile24, or Asn25 facilitate high yields (30–75 mg/L), and produced an enzyme with activity identical to wild type mTGase fromS. mobarensis. Site-specific antibody drug conjugates made with theE. coliproduced mTGase demonstrated identical potency in anin vitrocell assay to those made with mTGase fromS. mobarensis.