Study On The Function And Mechanism Of The C-tcrminal Domain Of Legionella. Pneumophila Effector SdeA

Ubiquitination regulates almost all key cellular process in eukaryotic including endocytosis,autophagy,immunity and inflammation.A number of bacterial effector proteins have been reported to manipulate the ubiquitin(Ub)-pathway and counteract the post-translational modification in host cells.The effector SdeA of L.pneumophila catalyzes an E1-and E2-independent ubiquitination of host proteins via its mono-ADPribosyltransferase(mART)and phosphodiesterase(PDE)domains in the middle regions with NAD.SdeA also contains a deubiquitinase domain in N-terminus,which is important for ubiquitin dynamics on the bacterial phagosomes.In eukaryotic cells,most of Ub molecules are conjugated to be polyUb chains of different linkages.There are only few amount of free Ub in host cells.However,how SdeA senses polyUb chains for further processing by its deubiquitinase and mART-PDE domains in host cells remains unclear.Here,we show that a C-terminal region of SdeA(SdeA pCTD)specifically senses K63-linked polyUb chains and mediates the N-terminal deubiquitinase activity.We determined the crystals structure of SdeA pCTD in complex with K63-linked diUb at a resolution of 3.4 ?.The structure revealed that SdeA pCTD forms a dual-bundle architecture to contact the proximal and distal Ub,respectively,of the K63-linked diUb.The pCTD structure is distinct from the previously known structures of K63 polyUb-binding proteins.Mutations of the Ub-binding residues in pCTD reduced the deubiquitinase activity of SdeA towards K63-linked polyUb chains,suggesting that sensing polyUb chains by pCTD relieves the deubiquitinase autoinhibition of SdeA.This study uncovers a key role of pCTD in the SdeA function and highlights the successively precise hijacking of Ub by the pathogen in the host.