A family of Salmonella virulence factors functions as a distinct class of autoregulated E3 ubiquitin ligases.
Processes as diverse as receptor binding and signaling, cytoskeletal dynamics, and programmed cell death are manipulated by mimics of host proteins encoded by pathogenic bacteria. We show here that the Salmonella virulence factor SspH2 belongs to a growing class of bacterial effector proteins that harness and subvert the eukaryotic ubiquitination pathway. This virulence protein possesses ubiquitination activity that depends on a conserved cysteine residue. A crystal structure of SspH2 reveals a canonical leucine-rich repeat (LRR) domain that interacts with a unique E3 ligase [which we have termed NEL for Novel E3 Ligase] C-terminal fold unrelated to previously observed HECT or RING-finger E3 ligases. Moreover, the LRR domain sequesters the catalytic cysteine residue contained in the NEL domain, and we suggest a mechanism for activation of the ligase requiring a substantial conformational change to release the catalytic domain for function. We also show that the N-terminal domain targets SspH2 to the apical plasma membrane of polarized epithelial cells and propose a model whereby binding of the LRR to proteins at the target site releases the ligase domain for site-specific function.
Quezada
Cindy M
CM
Laboratory of Structural Microbiology, The Rockefeller University, New York, NY 10065, USA.
Hicks
Stuart W
SW
Galán
Jorge E
JE
Stebbins
C Erec
CE
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000472:pathogenicity*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism*; D054875:Ubiquitination; D037521:Virulence Factors / Q000378:metabolism*
D001426:Bacterial Proteins; D037521:Virulence Factors; D044767:Ubiquitin-Protein Ligases