Glutamine Deamidation and Dysfunction of Ubiquitin/NEDD8 Induced by a Bacterial Effector Family

A family of bacterial effectors including Cif homolog from Burkholderia pseudomallei (CHBP) and Cif from Enteropathogenic Escherichia coli (EPEC) adopt a functionally important papain-like hydrolytic fold. We show here that CHBP was a potent inhibitor of the eukaryotic ubiquitination pathway. CHBP acted as a deamidase that specifically and efficiently deamidated Gln40 in ubiquitin and ubiquitin-like protein NEDD8 both in vitro and during Burkholderia infection. Deamidated ubiquitin was impaired in supporting ubiquitin-chain synthesis. Cif selectively deamidated NEDD8, which abolished the activity of neddylated Cullin-RING ubiquitin ligases (CRLs). Ubiquitination and ubiquitin-dependent degradation of multiple CRL substrates were impaired by Cif in EPEC-infected cells. Mutations of substrate-contacting residues in Cif abolished or attenuated EPEC-induced cytopathic phenotypes of cell cycle arrest and actin stress fiber formation. Gram-negative bacterial pathogens use atype III secretion system (TTSS) to trans-locate effectors into eukaryotic host cells, serving as a key virulence mechanism (1, 2). Several effectors from different bacteria inhibit host cell cycle progression (3–6). Cif (cycle in-hibiting factor) from Enteropathogenic E. col