Endolysins are peptidoglycan (PG) hydrolases that function as part of the bacteriophage (phage) lytic system to release progeny phage at the end of a replication cycle. Notably, endolysins alone can produce lysis without phage infection, which offers an attractive alternative to traditional antibiotics. Endolysins from phage that infect Gram-positive bacterial hosts contain at least one enzymatically active domain (EAD) responsible for hydrolysis of PG bonds and a cell wall binding domain (CBD) that binds a cell wall epitope, such as a surface carbohydrate, providing some degree of specificity for the endolysin. Whilst the EADs typically cluster into conserved mechanistic classes with well-defined active sites, relatively little is known about the nature of the CBDs and only a few binding epitopes for CBDs have been elucidated. The major cell wall components of many streptococci are the polysaccharides that contain the polyrhamnose (pRha) backbone modified with species-specific and serotype-specific glycosyl side chains. In this report, using molecular genetics, microscopy, flow cytometry and lytic activity assays, we demonstrate the interaction of PlyCB, the CBD subunit of the streptococcal PlyC endolysin, with the pRha backbone of the cell wall polysaccharides, Group A Carbohydrate (GAC) and serotype c-specific carbohydrate (SCC) expressed by the Group A Streptococcus and Streptococcus mutans, respectively.
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Autophagy is an important component of the innate immune response that restricts infection by different types of pathogens. In this issue Ylä-Anttila and Masucci (pp. 2297–2308) demonstrate the inhibition of selective autophagy by various members of the herpesvirus upiquitin-deconjugase family. The cover image shows representative micrographs illustrating the colocalization of SQSTM1/p62 (red) with LC3 (green) in cells expressing the viral enzymes (grey). The nuclei were stained with DAPI (blue). Size bars = 10 µm. Image provided by Maria G. Masucci.
Molecular basis for recognition of the Group A Carbohydrate backbone by the PlyC streptococcal bacteriophage endolysin
Harley King, Sowmya Ajay Castro, Amol Arunrao Pohane, Cynthia M. Scholte, Vincent A. Fischetti, Natalia Korotkova, Daniel C. Nelson, Helge C. Dorfmueller; Molecular basis for recognition of the Group A Carbohydrate backbone by the PlyC streptococcal bacteriophage endolysin. Biochem J 25 June 2021; 478 (12): 2385–2397. doi: https://doi.org/10.1042/BCJ20210158
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