Regulation of the small GTPase Rab1 function by a bacterial glucosyltransferase

Abstract

Posttranslational modification of key host proteins by virulence factors is an important theme in bacterial pathogenesis. A remarkable example is the reversible modifications of the small GTPase Rab1 by multiple effectors of the bacterial pathogen Legionella pneumophila. Previous studies have shown that the effector SetA, dependent on a functional glucosyltransferase domain, interferes with host secretory pathways. However, the enzymatic substrate(s) of SetA in host cells remains unknown. Here, by using cross-linking mass spectrometry we uncovered Rab1 as the target of SetA during L. pneumophila infection. Biochemical studies establish that SetA covalently attaches a glucose moiety to Thr75 within the switch II region of Rab1, inhibiting its intrinsic GTPase activity. Moreover, we found that SetA preferentially modifies the GDP-bound form of Rab1 over its GTP-associated state and the modification of Rab1 inhibits its interaction with the GDP dissociation inhibitor GDI1, allowing for Rab1 activation. Our results thus add an extra layer of regulation on Rab1 activity and provide a mechanistic understanding of its inhibition of the host secretory pathways as well as cellular toxicity.

Interfering with Autophagy: The Opposing Strategies Deployed by Legionella pneumophila and Coxiella burnetii Effector Proteins

“…Recently a similar screen identified a cohort of effectors that promoted translocation of TFEB into the nucleus, including members of the SidE family, SdeA (Lpg2157) and SdeC (Lpg2153) confirming results observed by De Leon et al 2017, as well as identifying novel effectors: MavH (Lpg2425), VipD (Lpg2831), Lpg2552, Lpg2828, Lpg2888, and SetA (Lpg1978) (Beck et al, 2020). SetA is a mono-O-glucosyltransferase containing a DxD catalytic motif that preferentially uses UDP-glucose as a sugar donor targeting a range of host proteins including the small GTPase Rab1a, the chaperonin CCT5 and actin (Jank et al, 2012;Wang et al, 2018;Levanova et al, 2019;Gao et al, 2019). Beck et al (2020) show that translocation of TFEB into the nucleus is dependent on the glucosyltransferase activity of SetA and mass spectrometry revealed the sites on TFEB that are modified by SetA.…”

Arginine GlcNAcylation of Rab small GTPases by the pathogen Salmonella Typhimurium

“…AMPylation on Tyr77 by DrrA disrupts the ability of Rab1 to mediate vesicle transport within the secretory pathway in eukaryotic cells 39,40 . SetA glucosylates Rab1 at Thr75, thus attenuating its GTPase activity and inhibiting its interaction with the GDI-1 41 . Therefore, these findings stimulate our thinking of a new strategy adopted by Salmonella to target the host trafficking system.…”

The Salmonella Effector SseK3 Targets Small Rab GTPases

“…These changes may influence the ability of effectors to bind and modify the Rabs. For example, the Legionella glucosyltransferase effector, SetA preferentially modifies GDPbound Rab1 (Wang et al, 2018), and an endogenous Rab1 regulator, TAK1, also preferentially phosphorylates the GDPbound form of Rab1 (Levin et al, 2016). Thus, we explored whether SseK3 exhibited a preference for GTP-bound or FIGURE 3 | SseK3 modifies Arg74, Arg82, and Arg111 within Rab1a and has no preference for GTP-bound or GDP-bound Rab1a.…”