The bacteriophage lambda tail protein gpK is required for tail assembly. The activity of the protein can be found at the assembling tail tip and is believed to be localized to this structure. GpK is a 27 kDa protein that has sequence identity to two families of proteins: the Mov34 family of peptidases and the NlpC/P60 family of peptidoglycan endopeptidases. Point substitutions and complementation data confirm that gpK possesses each of these domains and that they can function in trans. When the Mov34 domain is inactivated tail assembly is disrupted whereas when the NlpC/P60 domain is inactivated tails assemble but are inactive. Evidence is presented here that the C-terminal domain possesses lytic activity in isolation but not when part of the full-length protein.

The bacteriophage lambda tail protein gpK is required for tail assembly. The activity of the protein can be found at the assembling tail tip and is believed to be localized to this structure. GpK is a 27 kDa protein that has sequence identity to two families of proteins: the Mov34 family of peptidases and the NlpC/P60 family of peptidoglycan endopeptidases. Point substitutions and complementation data confirm that gpK possesses each of these domains and that they can function in trans. When the Mov34 domain is inactivated tail assembly is disrupted whereas when the NlpC/P60 domain is inactivated tails assemble but are inactive. Evidence is presented here that the C-terminal domain possesses lytic activity in isolation but not when part of the full-length protein.

La chaperonine CCT/TriC tient un rôle central dans le maintien de la protéostase cellulaire. Elle compte parmi ses clientes un grand nombre de protéines impliquées de près ou de loin dans la régulation du cycle comme l’actine, la tubuline et la cycline E. afin de mieux comprendre l’implication de la CCT/TriC dans la cancérogenèse, nous avons quantifié, dans 18 lignées cellulaires tumorales, une lignée issue d’un tissu sain et un tissu sain, ses taux d’expression et son activité. Nos résultats indiquent que l’expression de la CCT/TriC n’est pas toujours corrélée à son activité. Nous avons dans un second temps, documenté l’expression de ces partenaires/modulateurs d’activité, préfoldine, PhLP3, Hop/p60, Hsp/c70 et leur influence sur son activité. Nos résultats montrent que l’activité de la CCT/TriC pourrait être régulée à travers les variations des niveaux d’expression de la préfoldine et/ ou Hsp/c 70. Enfin, nous avons montré que dans les cellules qui se divisent le plus lentement, l’activité de la CCT/TRiC est la plus faible. Ces observations montrent que les variations de l’activité de la CCT/TriC pourraient constituer un point de contrôle dans la prolifération cellulaire maligne. / The molecular chaperone CCT/TRiC plays a central role in maintaining cellular proteostasis. It mediates the folding of lot of proteins involved in cell cycle regulation as the major cytoskeletal proteins tubulins and actins and the oncoprotein cyclin E. To assess the involvement of CCT/TRiC in tumor genesis, we quantified its expression levels and activity in 18 cancer, one non-cancer human cell lines and a non-cancer human liver. We show that the expression levels of CCT/TRiC in cancer cell lines are higher than that in normal cells. However, CCT/TRiC activity does not always correlate with its expression levels. We therefore documented the expression levels of CCT/TRiC modulators and partners PhLP3, Hop/P60, prefoldin and Hsp/Hsc70. Our analysis reveals a functional interplay between molecular chaperones that might account for a precise modulation of CCT/TRiC activity in cell proliferation through changes in the cellular levels of prefoldin and/or Hsc/p70 and CCT/TRiC client protein availability. Finally, our study reveals that cells with the longest doubling time host the smallest CCT/TRiC activity suggesting that CCT/TRiC-mediated client protein folding constitutes a bottle-neck in cancer cell proliferation. Our observation and approaches bring novel insights in the role of CCT/TRiC-mediated protein folding machinery in cancer cell development.