Legionella pneumophila Chaperonin 60, an Extra-and Intra-Cellular Moonlighting Virulence-Related Factor

This chapter presents the many known anomalies of Legionella Pneumophila (HtpB) and a historical perspective of the research that led to the establishment of HtpB as a moonlighting chaperonin. It focuses on HtpB's moonlighting functions in all the cellular compartments where this chaperonin is found. HtpB is the only chaperonin in L. pneumophila, and a portion of it resides in extracytoplasmic bacterial locations either as a membrane-associated, periplasmic, or surface-exposed protein, playing unique protein-folding independent roles in each of these compartments. In an attempt to explain the phenotypes induced by recombinant HtpB in yeast and mammalian cells, the chapter conducts a number of yeast two-hybrid screenings to identify potential eukaryotic protein partners of HtpB. This screening identified yeast S-adenosyl methionine decarboxylase (SAMDC) as a specific partner of HtpB. HtpB and GroEL differ in a total of 137 amino acid positions scattered throughout the entire protein.