Detection of protein-protein interactions in bacteria by GFP-fragment reconstitution

Protein trans-splicing: optimization of intein-mediated GFP assembly as a model for the development of gene therapy

Adeno-associated virus (AAV)-based gene therapy has become one of the key directions of modern translational medicine geared towards treatment of hereditary disorders by means of gene replacement. At the moment, about 5,000 different syndromes are associated with mutations in large genes, which presents a great problem due to the AAV packaging capacity of 5 kilobases. The main strategies for overcoming this obstacle were the creation of truncated gene versions, overloading the viral vector, and separate delivery of partial genetic material to restore the whole gene at the level of DNA, RNA, or protein. At present, genome editing via prime editors, most effectively delivered by AAV, relies on the intein pair used to restore the protein complex. The amazing integration speed of intein-based protein trans splicing technology makes it a versatile tool for a variety of applications, albeit not always successful on the first attempt. This study discusses the key points of working with Ssp, Npu, and Ava inteins of the DnaE group, known as the most effective for assembly of large proteins. Using green fluorescent protein (GFP) as a model, we demonstrate that the successful protein assembly requires not only cysteine at position C+1 but also certain aminoacid residues on either side in its immediate environment. Furthermore, the conformation of extein-intein composition, difficult to predict by computer modeling, has an additional effect, as demonstrated by experimental tests of the three split sites optimal in amino acid composition. The NpuDnaE variant demonstrated the highest kinetics of interaction between the N and C parts in the DnaE group of inteins. Optimization of conditions using NpuDnaE intein led to GFP assembly in 80% of transfected HEK293 cells and in 55% of AAV5-transduced cells, as demonstrated by flow cytometry. The efficiency of GFP assembly post-plasmid DNA transfection or AAV transduction of the HEK293 cell line was 15% higher than that of the ARPE19 cell line. We hope that the obtained data will facilitate the development of gene therapies for the treatment of hereditary disorders caused by mutations in large genes.

The Role of the Microbiota in Regeneration-Associated Processes

The microbiota, the set of microorganisms associated with a particular environment or host, has acquired a prominent role in the study of many physiological and developmental processes. Among these, is the relationship between the microbiota and regenerative processes in various organisms. Here we introduce the concept of the microbiota and its involvement in regeneration-related cellular events. We then review the role of the microbiota in regenerative models that extend from the repair of tissue layers to the regeneration of complete organs or animals. We highlight the role of the microbiota in the digestive tract, since it accounts for a significant percentage of an animal microbiota, and at the same time provides an outstanding system to study microbiota effects on regeneration. Lastly, while this review serves to highlight echinoderms, primarily holothuroids, as models for regeneration studies, it also provides multiple examples of microbiota-related interactions in other processes in different organisms.

Biotechnological Applications of Protein Splicing

Protein splicing domains, also called inteins, have become a powerful biotechnological tool for applications involving molecular biology and protein engineering. Early applications of inteins focused on self-cleaving affinity tags, generation of recombinant polypeptide α-thioesters for the production of semisynthetic proteins and backbone cyclized polypeptides. The discovery of naturallyoccurring split-inteins has allowed the development of novel approaches for the selective modification of proteins both in vitro and in vivo. This review gives a general introduction to protein splicing with a focus on their role in expanding the applications of intein-based technologies in protein engineering and chemical biology.

Cell Penetrating Peptides for Chemical Biological Studies

Significant progress has been made in the development of chemical biology methods used to study the molecular behavior and interplay among live cells. These include the development of novel fluorescent molecules and photo-cross-linking agents that can be used to determine the cellular locations of biomacromolecules (including proteins and nucleic acids). Various biosensors utilizing the remarkable ligand-recognition abilities of biomacromolecules have also been developed. To allow such chemically functionalized molecules to interact with their partners, and to fully exploit the abilities and functions thereof, it is necessary to efficiently deliver such molecules into cells, specifically into the cytosol. Here, we illustrate intracellular delivery methods employing arginine-rich cell-penetrating peptides (CPPs) (e.g., octa-arginine) in the presence of a counteranion, pyrenebutyrate. This approach is especially suitable for intracellular delivery of small proteins and peptides. Approaches employing arginine-rich CPPs tagged with a penetration-accelerating sequence can also be used toward this end.

Detecting protein-protein interactions based on kinase-mediated growth induction of mammalian cells

Detection of protein–protein interactions (PPIs) is important for understanding numerous processes in mammalian cells; however, existing PPI detection methods often give significant background signals. Here, we propose a novel PPI-detection method based on kinase-mediated growth induction of mammalian cells. In this method, target proteins are fused to the intracellular domain of c-kit (c-kit ICD) and expressed in interleukin-3-dependent mammalian cells. The PPI induces dimerization and activation of c-kit ICDs, which leads to cell growth in the absence of interleukin-3. Using this system, we successfully detected the ligand-dependent homo-interaction of FKBP_F36V and hetero-interaction of FKBP and FRB_T2098L, as well as the constitutive interaction between MDM2 and a known peptide inhibitor. Intriguingly, cells expressing high-affinity peptide chimeras are selected from the mixture of the cell populations dominantly expressing low-affinity peptide chimeras. These results indicate that this method can detect PPIs with low background levels and is suitable for peptide inhibitor screening.

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.

Protein-protein interaction networks: unraveling the wiring of molecular machines within the cell

Mapping and understanding of the protein interaction networks with their key modules and hubs can provide deeper insights into the molecular machinery underlying complex phenotypes. In this article, we present the basic characteristics and definitions of protein networks, starting with a distinction of the different types of associations between proteins. We focus the review on protein-protein interactions (PPIs), a subset of associations defined as physical contacts between proteins that occur by selective molecular docking in a particular biological context. We present such definition as opposed to other types of protein associations derived from regulatory, genetic, structural or functional relations. To determine PPIs, a variety of binary and co-complex methods exist; however, not all the technologies provide the same information and data quality. A way of increasing confidence in a given protein interaction is to integrate orthogonal experimental evidences. The use of several complementary methods testing each single interaction assesses the accuracy of PPI data and tries to minimize the occurrence of false interactions. Following this approach there have been important efforts to unify primary databases of experimentally proven PPIs into integrated databases. These meta-databases provide a measure of the confidence of interactions based on the number of experimental proofs that report them. As a conclusion, we can state that integrated information allows the building of more reliable interaction networks. Identification of communities, cliques, modules and hubs by analysing the topological parameters and graph properties of the protein networks allows the discovery of central/critical nodes, which are candidates to regulate cellular flux and dynamics.