Characterization of a novel intramolecular chaperone domain conserved in endosialidases and other bacteriophage tail spike and fiber proteins.
Folding and assembly of endosialidases, the trimeric tail spike proteins of Escherichia coli K1-specific bacteriophages, crucially depend on their C-terminal domain (CTD). Homologous CTDs were identified in phage proteins belonging to three different protein families: neck appendage proteins of several Bacillus phages, L-shaped tail fibers of coliphage T5, and K5 lyases, the tail spike proteins of phages infecting E. coli K5. By analyzing a representative of each family, we show that in all cases, the CTD is cleaved off after a strictly conserved serine residue and alanine substitution prevented cleavage. Further structural and functional analyses revealed that (i) CTDs are autonomous domains with a high alpha-helical content; (ii) proteolytically released CTDs assemble into hexamers, which are most likely dimers of trimers; (iii) highly conserved amino acids within the CTD are indispensable for CTD-mediated folding and complex formation; (iv) CTDs can be exchanged between proteins of different families; and (v) proteolytic cleavage is essential to stabilize the native protein complex. Data obtained for full-length and proteolytically processed endosialidase variants suggest that release of the CTD increases the unfolding barrier, trapping the mature trimer in a kinetically stable conformation. In summary, we characterize the CTD as a novel C-terminal chaperone domain, which assists folding and assembly of unrelated phage proteins.
Schwarzer
David
D
Abteilung Zelluläre Chemie, Zentrum Biochemie, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
Stummeyer
Katharina
K
Gerardy-Schahn
Rita
R
Mühlenhoff
Martina
M
D017103:Bacillus Phages / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D003090:Coliphages / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics*; D017124:Conserved Sequence; D017931:DNA Primers; D004926:Escherichia coli / Q000821:virology; D006026:Glycoside Hydrolases; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics*; D008969:Molecular Sequence Data; D009439:Neuraminidase / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics*; D017376:Viral Tail Proteins / Q000737:chemistry* / Q000235:genetics*
D017931:DNA Primers; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D014764:Viral Proteins; D017376:Viral Tail Proteins; D006026:Glycoside Hydrolases; C035355:endo-N-acetylneuraminidase; C083268:tailspike protein, bacteriophage; D009439:Neuraminidase