Protein cleavable fusion

Tolbert TJ, Franke D, Wong CH. A new strategy for glycoprotein synthesis ligation of synthetic glycopeptides with truncated proteins expressed in E. coli as TEV protease cleavable fusion protein. Bioorg. Med. Chem. 2005 13 909-915. 

When looking at the examples shown in Figure 12.1, or at the large set of proteins not shown here, two general trends are obvious (i) the ubiquitin domain tends to be localized at the extreme N-terminus, and (ii) the host protein is typically involved in the ubiquitin system. The first observation has been interpreted as an evolutionary remnant of earlier ubiquitin-fusion proteins [40]. As mentioned above, ubiquitin is typically expressed as a precursor protein, wherein the ubiquitin moiety is localized at the N -terminus and has to be liberated by dedicated ubiquitin hydrolases. It is certainly possible that many extant proteins with ubiquitin-like domains used to be alternative ubiquitin precursors but have lost their cleavability. The second observation will be discussed in more detail in Sections 12.5.1 and 12.5.2. 

Grafting of PEG on the liposome surface interferes with the ability of the liposome to undergo membrane fusion and destabilization in the endosome. Meyer et al. observed this point (33). The stabilization of the lipopiexes into a lamellar phase would be a possible reason for this transfection inhibition, by lack of destabilization into the endosome (34). Thus, cleavable PEG-lipid has been designed to limit the nonspecific interaction with proteins, although restoring the ability of the particles to interact with the endosomal cellular membranes and to release their therapeutic payload. 

Whereas cleavable linkers seem less relevant with respect to engineering functional interactions between P450 and redox partner(s), flexible and rigid hnkers have been used frequently to construct a variety of artificial fusion proteins with the aim to increase the efficiency of electron transfer and improve the catalytic efficiency of the P450 system. 

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