Structural Biology Of Novel Ubiquitination And Deubiquitination Reactions Mediated By Legionella Pneumophila Effector Proteins MavC And MvcA

After invading host cells,Legionella pneumophila can delay host cell apoptosis by secreting a series of effector proteins with the help of ubiquitination modification,and accelerate its own reproduction.It is the main pathogen that causes host infection of Legionella pneumonia.Ubiquitin is a small molecule protein that can participate in many important physiological activities such as apoptosis.It can complete the ubiquitination of the protein by covalently linking it with the target protein to carry the ubiquitin tag.The traditional ubiquitination process is a classic three-enzyme cascade,while the effector protein of Legionella pneumophila,MavC,can catalyze the ubiquitination of the substrate UBE2 N in an unconventional manner,and the ubiquitination process can be completed in only two steps.At the same time,another effector protein of Legionella pneumophila,MvcA,can deubiquitinate the novel ubiquitination product catalyzed by MavC.The two effector proteins share about 50% homology in amino acid sequence,but are almost completely opposite in function.In addition,Lpg2149,another effector protein in Legionella pneumophila,can simultaneously inhibit the ubiquitination of MavC and the deubiquitination of MvcA,thereby regulating the activities of both.But the molecular mechanism of the above process has not been clearly studied.Here,we analyzed the structure of MvcA and its substrate,UBE2N-Ub protein catalyzed by MavC.We also analyzed the complex structure of MvcA and its inhibitor Lpg2149,in order to explain the molecular mechanism of MvcA deubiquitination and the inhibition mechanism of Lpg2149 on MvcA activity.After comparing the structures of the two effector proteins,MavC and MvcA,and their related complex structures,combined with a variety of protein interaction detection methods,this paper proposes the molecular mechanism of MavC and MvcA,two proteins that are highly similar in sequence but exhibit almost diametrically opposite activities.In the meantime,we also designed a series of mutants in which the residues of MavC and MvcA are exchanged near the active site.And by changing individual residues,a MavC mutant protein with reversed activity was obtained.The work of this paper has profound implications for our understanding of the functional evolution of proteins and the relationship between protein structure and function.At the same time,the structural biology research on MavC and MvcA also laid a structural foundation for the design of inhibitors of the two and related reagents for the treatment of Legionella pneumonia in the future.