Reconstitution of surface lipoprotein translocation through the Slam translocon

Abstract

Surface lipoproteins (SLPs) are peripherally attached to the outer leaflet of the outer membrane in many Gram-negative bacteria, playing significant roles in nutrient acquisition and immune evasion in the host. While the factors that are involved in the synthesis and delivery of SLPs in the inner membrane are well characterized, the molecular machinery required for the movement of SLPs to the surface are still not fully elucidated. In this study, we investigated the translocation of a SLP TbpB through a Slam1-dependent pathway. Using purified components, we developed an in vitro translocation assay where unfolded TbpB is transported through Slam1-containing proteoliposomes, confirming Slam1 as an outer membrane translocon. While looking to identify factors to increase translocation efficiency, we discovered the periplasmic chaperone Skp interacted with TbpB in the periplasm of Escherichia coli. The presence of Skp was found to increase the translocation efficiency of TbpB in the reconstituted translocation assays. A knockout of Skp in Neisseria meningitidis revealed that Skp is essential for functional translocation of TbpB to the bacterial surface. Taken together, we propose a pathway for surface destined lipoproteins, where Skp acts as a holdase for Slam-mediated TbpB translocation across the outer membrane.

Unmasking of the von Willebrand A-domain surface adhesin CglB at bacterial focal adhesions mediates myxobacterial gliding motility

“…The TbpA/LbpA β barrels contain a Ton box and are TonB-dependent transporters (parallel: GltA/B), which can then import the abstracted iron into the cell upon activation of the integral IM ExbBD-TonB (parallel: AglRQS) motor (43,44). Recently, a previously unknown class of transporter (corresponding to DUF560) has been shown to mediate secretion of lipoproteins such as TbpB/LbpB (and soluble proteins) across the OM (45)(46)(47)(48). However, such a proposed "Type 11 secretion system" is not encoded in the M. xanthus genome, suggesting that this is not the mechanism for CglB trans-OM export.…”

Synergistic vesicle-vector systems for targeted delivery

“…These surface lipoproteins (SLPs) perform crucial functions in regard to food uptake, immunological evasion, cellular adhesion, and cell signaling and are turally and functionally varied [ 109 ]. Additionally, surface lipoproteins can be used as carrier proteins for cell-surface display of heterologous proteins [ 110 ] (Fig. 4 d).…”

Bacterial surface‐exposed lipoproteins and sortase‐mediated anchored cell surface proteins in plant infection

“…Diderm and monoderm bacteria produce lipoproteins, being the periplasm the predominant localization site for most lipoproteins in diderms (Figures 1 and 2 ). Due to the identification of the outer membrane protein translocons, SLAM and Bam, in recent years, there has been an increased discovery of surface‐exposed lipoproteins that are embedded in the periplasmatic side of the outer membrane and exposed to the surface (Figure 2 ) (El Rayes et al, 2021 ; Huynh et al, 2022 ; Kovacs‐Simon et al, 2011 ; Remans et al, 2010 ; Wilson & Bernstein, 2016 ), which leads us to question the implications of these proteins in cell function. For instance, more than half of the 175 predicted lipoproteins in the genome of Pseudomonas aeruginosa are classified as hypothetical proteins for which a function, and thus their involvement in pathogenesis, remains to be determined (Nguyen et al, 2020 ; Remans et al, 2010 ).…”