Investigations on the activation of recombinant microbial pro-transglutaminase: in contrast to proteinase K, dispase removes the histidine-tag.

In order to produce recombinant microbial transglutaminase (rMTG) which is free of the activating protease, dispase was used to activate the pro-rMTG followed by immobilized metal affinity chromatography (IMAC). As shown by MALDI-MS, the dispase does not only cleave the pro-sequence, but unfortunately also cleaves within the C-terminal histidine-tag. Hence, the active rMTG cannot properly bind to the IMAC material. As an alternative, proteinase K was investigated. This protease was successfully applied for the activation of purified pro-rMTG either as free or immobilized enzyme and the free enzyme was also applicable directly in the crude cell extract of E. coli. Thus, it enables a simple two-step activation/purification procedure resulting in protease-free and almost pure transglutaminase preparations. The protocol has been successfully applied to both, wild-type transglutaminase of Streptomyces mobaraensis as well as to the highly active variant S2P. Proteinase K activates the pro-rMTG without unwanted degradation of the histidine-tag. It turned out to be very important to inhibit proteinase K activity, e.g., by PMSF, prior to protein separation by SDS-PAGE.