TAT-MeCP2 protein variants rescue disease phenotypes in human and mouse models of Rett syndrome

Construction and in vitro activity evaluation of protein transduction domain-transactivator of transcription and Candida antarctica lipase B fusion proteins

Protein transduction domain (PTD)- transactivator of transcription (Tat) and the alkaline cold-active lipase Candida antarctica lipase B (calB) were used to construct a calB-Tat recombinant protein and examine its membrane-penetrating ability. The calB gene was fused with a PTD-Tat-encoding fragment to create the in-frame calB-Tat. After digestion with Nco I and Xho I, the calB-Tat fragment was subcloned and inserted into the expression vector pET28a. The recombinant plasmid pET28a-calB-Tat was subsequently transferred into E.coli Rosetta (DE3) cells to express the labeled protein calB-Tat. Protein concentrations were measured using a commercial BCA kit, and the transmembrane activity of the proteins in SH-SY5Y cells was observed under a fluorescence-inverted microscope. MTT and Western blotting assays were conducted to examine toxicity. The fusion protein exhibited low toxicity. As the concentration of the fusion protein decreased, the effect on cell viability decreased. Additionally, the fusion protein penetrated the cell membrane penetration was stable and was specifically expressed in cells. Taken together, the pET28a-calB-Tat prokaryotic vector was generated, yielding a significant amount of the calB-Tat protein. This increased the cell membrane and perhaps reveals a new way of delivering weight-loss drugs and protein-based medications.

MeCP2 is a naturally supercharged protein with cell membrane transduction capabilities

The intrinsically disordered protein MeCP2 is a global transcriptional regulator encoded by the MECP2 gene. Although the structured domains of MeCP2 have been the subject of multiple studies, its unstructured regions have not been that extensively characterized. In this work, we show that MeCP2 possesses properties akin to those of supercharged proteins. By utilizing its unstructured portions, MeCP2 can successfully transduce across cell membranes and localize to heterochromatic foci in the nuclei, displaying uptake levels a third lower than a MeCP2 construct fused to the cell-penetrating peptide TAT. MeCP2 uptake can further be enhanced by the addition of compounds that promote endosomal escape following cellular trafficking by means of macropinocytosis. Using a combination of in silico prediction algorithms and live-cell imaging experiments, we mapped the sequence in MeCP2 responsible for its cellular incorporation, which bears a striking resemblance to TAT itself. Transduced MeCP2 was shown to interact with HDAC3. These findings provide valuable insight into the properties of MeCP2 and may be beneficial for devising future protein-based treatment strategies.

Dose-Dependent Nuclear Delivery and Transcriptional Repression with a Cell-Penetrant MeCP2

The vast majority of biologic-based therapeutics operate within serum, on the cell surface, or within endocytic vesicles, in large part because proteins and nucleic acids fail to efficiently cross cell or endosomal membranes. The impact of biologic-based therapeutics would expand exponentially if proteins and nucleic acids could reliably evade endosomal degradation, escape endosomal vesicles, and remain functional. Using the cell-permeant mini-protein ZF5.3, here we report the efficient nuclear delivery of functional Methyl-CpG-binding-protein 2 (MeCP2), a transcriptional regulator whose mutation causes Rett syndrome (RTT). We report that ZF-tMeCP2, a conjugate of ZF5.3 and MeCP2(Δaa13-71, 313-484), binds DNA in a methylation-dependent manner in vitro, and reaches the nucleus of model cell lines intact to achieve an average concentration of 700 nM. When delivered to live cells, ZF-tMeCP2 engages the NCoR/SMRT corepressor complex, selectively represses transcription from methylated promoters, and colocalizes with heterochromatin in mouse primary cortical neurons. We also report that efficient nuclear delivery of ZF-tMeCP2 relies on an endosomal escape portal provided by HOPS-dependent endosomal fusion. The Tat conjugate of MeCP2 (Tat-tMeCP2), evaluated for comparison, is degraded within the nucleus, is not selective for methylated promoters, and trafficks in a HOPS-independent manner. These results support the feasibility of a HOPS-dependent portal for delivering functional macromolecules to the cell interior using the cell-penetrant mini-protein ZF5.3. Such a strategy could broaden the impact of multiple families of biologic-based therapeutics.