Cyclization tag for the detection and facile purification of backbone-cyclized proteins

Inteins in Science: Evolution to Application

Inteins are mobile genetic elements that apply standard enzymatic strategies to excise themselves post-translationally from the precursor protein via protein splicing. Since their discovery in the 1990s, recent advances in intein technology allow for them to be implemented as a modern biotechnological contrivance. Radical improvement in the structure and catalytic framework of cis- and trans-splicing inteins devised the development of engineered inteins that contribute to various efficient downstream techniques. Previous literature indicates that implementation of intein-mediated splicing has been extended to in vivo systems. Besides, the homing endonuclease domain also acts as a versatile biotechnological tool involving genetic manipulation and control of monogenic diseases. This review orients the understanding of inteins by sequentially studying the distribution and evolution pattern of intein, thereby highlighting a role in genetic mobility. Further, we include an in-depth summary of specific applications branching from protein purification using self-cleaving tags to protein modification, post-translational processing and labelling, followed by the development of intein-based biosensors. These engineered inteins offer a disruptive approach towards research avenues like biomaterial construction, metabolic engineering and synthetic biology. Therefore, this linear perspective allows for a more comprehensive understanding of intein function and its diverse applications.

Detection and purification of backbone-cyclized proteins using a bacterially expressed anti-myc-tag single chain antibody

A myc-tag and of which recognition by an antibody 9E10 has long been used for the detection and purification of recombinant proteins. We have previously expanded the application of the tag to the specific detection and purification of backbone-cyclized proteins. Here we sought a more practical way to using the 9E10 antibody by expressing its single chain antibody (scAb) form in Escherichia coli. The combined use of a strong T7 promoter and auto-induction strategy rather than early to mid-log induction of a Lac promoter resulted in the soluble over-expression of 9E10 scAb. However, the co-expression of a chaperone, Skp, was absolutely necessary for the activity even when the protein was expressed in a soluble manner. We could purify about 4 mg of 9E10 scAb from 1 l of culture, and the resulting scAb could be used to detect and purify the backbone-cyclized protein as the parental full-length 9E10. Moreover, the immunoaffinity resin prepared using 9E10 scAb could be regenerated several times after the elution of bound proteins using an acid, which added more value to the ready preparation of the active antibody in bacteria.

Intein applications: from protein purification and labeling to metabolic control methods

The discovery of inteins in the early 1990s opened the door to a wide variety of new technologies. Early engineered inteins from various sources allowed the development of self-cleaving affinity tags and new methods for joining protein segments through expressed protein ligation. Some applications were developed around native and engineered split inteins, which allow protein segments expressed separately to be spliced together in vitro. More recently, these early applications have been expanded and optimized through the discovery of highly efficient trans-splicing and trans-cleaving inteins. These new inteins have enabled a wide variety of applications in metabolic engineering, protein labeling, biomaterials construction, protein cyclization, and protein purification.