| Structural highlights
Function
[SDEA_LEGPH] Secreted effector that interferes with the host cell ubiquitin pathway and is required for intracellular bacterial replication. Catalyzes the ubiquitination of several mammalian Rab proteins (Rab33b, Rab1, Rab6a and Rab30) during L.pneumophila infection, without engaging the standard cellular enzyme cascade (E1 and E2). Transfers an ADP-ribose moiety from NAD to the 'Arg-42' residue of ubiquitin in a reaction that releases nicotinamide. The modified ubiquitin is subsequently transferred to the substrate protein through an unknown mechanism that results in the release of AMP. Cannot ubiquitinate the endosomal Rab5 or the cytoskeletal small GTPase Rac1 (PubMed:27049943). Also acts as a deubiquitinase (DUB), catalyzing the cleavage of three of the most abundant polyubiquitin chains ('Lys-11', 'Lys-48' and 'Lys-63') with a distinct preference for 'Lys-63' linkages; is thus able to efficiently remove 'Lys-63'-linked polyubiquitin chains from the phagosomal surface. Is also able to remove NEDD8 from neddylated proteins, but is unable to recognize SUMO. The DUB activity of SdeA is important for regulating the dynamics of ubiquitin association with the bacterial phagosome, but is dispensable for its role in intracellular bacterial replication (PubMed:26598703).[1] [2]
Publication Abstract from PubMed
Conventional ubiquitination regulates key cellular processes by catalysing the ATP-dependent formation of an isopeptide bond between ubiquitin (Ub) and primary amines in substrate proteins (1) . Recently, the SidE family of bacterial effector proteins (SdeA, SdeB, SdeC and SidE) from pathogenic Legionella pneumophila were shown to use NAD(+) to mediate phosphoribosyl-linked ubiquitination of serine residues in host proteins(2, 3). However, the molecular architecture of the catalytic platform that enables this complex multistep process remains unknown. Here we describe the structure of the catalytic core of SdeA, comprising mono-ADP-ribosyltransferase (mART) and phosphodiesterase (PDE) domains, and shed light on the activity of two distinct catalytic sites for serine ubiquitination. The mART catalytic site is composed of an alpha-helical lobe (AHL) that, together with the mART core, creates a chamber for NAD(+) binding and ADP-ribosylation of ubiquitin. The catalytic site in the PDE domain cleaves ADP-ribosylated ubiquitin to phosphoribosyl ubiquitin (PR-Ub) and mediates a two-step PR-Ub transfer reaction: first to a catalytic histidine 277 (forming a transient SdeA H277-PR-Ub intermediate) and subsequently to a serine residue in host proteins. Structural analysis revealed a substrate binding cleft in the PDE domain, juxtaposed with the catalytic site, that is essential for positioning serines for ubiquitination. Using degenerate substrate peptides and newly identified ubiquitination sites in RTN4B, we show that disordered polypeptides with hydrophobic residues surrounding the target serine residues are preferred substrates for SdeA ubiquitination. Infection studies with L. pneumophila expressing substrate-binding mutants of SdeA revealed that substrate ubiquitination, rather than modification of the cellular ubiquitin pool, determines the pathophysiological effect of SdeA during acute bacterial infection.
Insights into catalysis and function of phosphoribosyl-linked serine ubiquitination.,Kalayil S, Bhogaraju S, Bonn F, Shin D, Liu Y, Gan N, Basquin J, Grumati P, Luo ZQ, Dikic I Nature. 2018 May;557(7707):734-738. doi: 10.1038/s41586-018-0145-8. Epub 2018 May, 23. PMID:29795347[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Sheedlo MJ, Qiu J, Tan Y, Paul LN, Luo ZQ, Das C. Structural basis of substrate recognition by a bacterial deubiquitinase important for dynamics of phagosome ubiquitination. Proc Natl Acad Sci U S A. 2015 Nov 23. pii: 201514568. PMID:26598703 doi:http://dx.doi.org/10.1073/pnas.1514568112
- ↑ Qiu J, Sheedlo MJ, Yu K, Tan Y, Nakayasu ES, Das C, Liu X, Luo ZQ. Ubiquitination independent of E1 and E2 enzymes by bacterial effectors. Nature. 2016 May 5;533(7601):120-4. doi: 10.1038/nature17657. Epub 2016 Apr 6. PMID:27049943 doi:http://dx.doi.org/10.1038/nature17657
- ↑ Kalayil S, Bhogaraju S, Bonn F, Shin D, Liu Y, Gan N, Basquin J, Grumati P, Luo ZQ, Dikic I. Insights into catalysis and function of phosphoribosyl-linked serine ubiquitination. Nature. 2018 May;557(7707):734-738. doi: 10.1038/s41586-018-0145-8. Epub 2018 May, 23. PMID:29795347 doi:http://dx.doi.org/10.1038/s41586-018-0145-8
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