Tick-borne encephalitis virus (TBEV) causes 5−7 thousand cases of human meningitis and encephalitis annually. The neutralizing and protective antibody ch14D5 is a potential therapeutic agent. This antibody exhibits a high affinity for binding with the D3 domain of the glycoprotein E of the Far Eastern subtype of the virus, but a lower affinity for the D3 domains of the Siberian and European subtypes. In this study, a 2.2-fold increase in the affinity of single-chain antibody sc14D5 to D3 proteins of the Siberian and European subtypes of the virus was achieved using rational design and computational modeling. This improvement can be further enhanced in the case of the bivalent binding of the full-length chimeric antibody containing the identified mutation.

In this study, the impact of the genomic scaffold on the properties of bacteriophages was investigated by swapping the genomic scaffolds surrounding the tailspike genes between two Przondovirus phages, KP192 and KP195, which infect Klebsiella pneumoniae with different capsular types. A yeast-based transformation-associated recombination cloning technique and subsequent “rebooting” of synthetic phage genomes in bacteria were used to construct the phages. Using Klebsiella strains with K2, K64, and KL111 capsular types, it was shown that the capsular specificity of the synthetic phages is fully consistent with that of the tailspike proteins (tsp). However, the efficiency of plating and the lytic efficiency of these phages strongly depended on the genomic scaffold used and the Klebsiella strain used. Synthetic phages with swapped genomic scaffolds demonstrated superior reproduction efficiency using a number of strains compared to wild-type phages, indicating that some elements of the swapped genomic scaffold enhance phage replication efficiency, presumably by blocking some of the host anti-phage defense systems. Our findings demonstrate that even in the case of closely related phages, the selection of the genomic scaffold used for tsp gene transplantation can have a profound impact on the efficiency of phage propagation on target bacterial strains.

Bacteriophage receptor-binding proteins are often attached to the tail via a conserved N-terminal adapter/anchor domain, presumed to function independently from the distal receptor-binding/catalytic domain. Using synthetic phage technology, we demonstrated that the N-terminal domain in Przondovirus phages KP192 and KP195 substantially modulates the receptor-binding and hydrolytic activities of their type A tailspikes. A bioinformatics analysis of related proteins revealed a high correlation between the N-terminal domain and the distal receptor-binding region. Furthermore, it was shown that an imperfect structural fit between the N-terminal domain and the adjacent tail proteins (gatekeeper and nozzle proteins) can reduce virion assembly efficiency, thereby impairing phage fitness. These results underscore the importance of selecting an appropriate N-terminal domain of receptor-binding proteins when engineering bacteriophages with altered host specificity.

In this study, synthetic phages with swapped tailspike protein genes were constructed based on Przondovirus bacteriophages KP32_192 and KP32_195, which infect Klebsiella pneumoniae of different capsular serotypes. The specificity of these phages has changed in accordance with the genes of tailspike proteins. However, the reproduction efficiency of these phages strongly depended on the phage scaffold used, the sequence of the N-terminal domain of tail-anchored spikes, and the Klebsiella strain used. Moreover, phages with a non-native scaffold replicated on one of the strains more efficiently than wild-type phage with the same tailspikes. It has also been shown that the sequence of the N-terminal domain of tail-anchored spikes can influence the efficiency of phage adsorption. Therefore, it is necessary to consider not only the capsular specificity of tailspike proteins but also some other genes in the recipient phage genome when designing synthetic phages against the target bacterium.

Bacteriophage receptor-binding proteins are often attached to the tail via a conserved N-terminal adapter/anchor domain, presumed to function independently from the distal receptor-binding/catalytic domain. Using synthetic phage technology, we demonstrated that the N-terminal domain in Przondovirus phages KP192 and KP195 substantially modulates the receptor-binding and hydrolytic activities of their type A tailspikes. A bioinformatics analysis of related proteins revealed a high correlation between the N-terminal domain and the distal receptor-binding region. Furthermore, it was shown that an imperfect structural fit between the N-terminal domain and the adjacent tail proteins (gatekeeper and nozzle proteins) can reduce virion assembly efficiency, thereby impairing phage fitness. These results underscore the importance of selecting an appropriate N-terminal domain of receptor-binding proteins when engineering bacteriophages with altered host specificity.