Endolysins are bacteriophage-encoded peptidoglycan hydrolases, which are synthesized in the end of phage reproduction cycle, in an infected host cell. Usually, for endolysins from phages that infect Gram-positive bacteria, a modular structure is typical. Therefore, these are composed of at least two separate functional domains: an N-terminal catalytic domain (EAD) and a C-terminal cell wall binding domain (CBD). Specific ligand recognition of CBDs and following peptidoglycan (PG) binding mostly allows a rapid lytic activity of an EAD. Here we briefly characterize phage endolysin CBDs in conjuction with their domain architecture, (non)necessity for the following lytic activity and a high/low specificity of their ligands as well. Such an overall assessment of CBDs may help to find new ways to widen opportunities in their protein design to create ‛designer recombinant endolysins’ with diverse applications.

Production of recombinant proteins in Escherichia coli expression systems has shown many advantages, as well as disadvantages, especially for biotechnological and other down-stream applications. The choice of an appropriate vector depends on the gene, to be cloned for purification procedures and other analyses. Selection of a suitable production strain plays an important role in the preparation of recombinant proteins. The main criteria for the selection of the host organism are the properties of the recombinant produced protein, its subsequent use and the total amount desired. The most common problems in eukaryotic gene expression and recombinant proteins purification are, for instance, post-translational modifications, formation of disulphide bonds, or inclusion bodies. Obtaining a purified protein is a key step enabling further characterization of its role in the biological system. Moreover, methods of protein purification have been developed in parallel with the discovery of proteins and the need for their studies and applications. After protein purification, and also between the individual purification steps, it is necessary to test protein stability under different conditions over time. Shortly, all the essential points have been briefly discussed, which could be encountered during production and purification of a recombinant protein of interest, especially from eukaryotic source and expressed heterogeneously in prokaryotic production system.

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