Seminars

Pathogenic bacteria or viruses alter the host-ubiquitination system, which is critical for the host defense mechanisms upon infection. Among them, Legionella pneumophilia, an intracellular pathogenic bacterium, injects SidE family effectors into the host cells. SidE family has been implicated in unconventional phosphoribosyl-linked serine ubiquitination (PR-ubiquitination). Unlike the conventional ubiquitination, the SidE family catalyzes NAD+ and does not require E1, E2, E3 enzyme cascades. Legionella also have two genes encoding DeUbiquitinase for Phosphoribosyl-ubiquitination (DUPs, DupA/B) that specifically cleave PR-ubiquitin from serine residues on host substrates. More recently, several studies identified human OTU-like DUBs from Legionella and named them Legionella OTU like DUBs (Lot). Lots include LotA (Lpg2248/ Lem21), LotB (Lpg1621/ Ceg23), LotC (Lpg2529/ Lem27), and LotD (Lpg0227/ Ceg7). Similar to human OTUs, Lot DUBs exhibit linkage specificity. LotB and LotC prefer the K63- and K48-linkage, respectively. In contrast, Ceg7 cleaves K6-, K11-, K33-, K48-, and K63-linkage. Interestingly, LotA comprises two OTU-like domains with two catalytic cysteine residues (C13 and C303). The first OTU domain of LotA (LotA OTU1) exclusively cleaves the K6- linkage, whereas the second OTU domain (LotA OTU2) cleaves K48- and K63-linkages. Despite various efforts, however, the conserved molecular mechanism of this unique pathogenic DUBs has not been clearly understood. In this study, therefore, we investigated the structure and molecular mechanism of Lots. We found that Lots share a unique structural topology that is not found in any other OTUs. In addition, the catalytic triads of Lots were revealed to have differences compared to other OTUs. Moreover, we also provide molecular insights into how Lots distinguishes specific Ub-linkage types and the length of ubiquitin chains.