Two-step membrane binding by the bacterial SRP receptor enable efficient and accurate Co-translational protein targeting

Abstract

The signal recognition particle (SRP) delivers ~30% of the proteome to the eukaryotic endoplasmic reticulum, or the bacterial plasma membrane. The precise mechanism by which the bacterial SRP receptor, FtsY, interacts with and is regulated at the target membrane remain unclear. Here, quantitative analysis of FtsY-lipid interactions at single-molecule resolution revealed a two-step mechanism in which FtsY initially contacts membrane via a Dynamic mode, followed by an SRP-induced conformational transition to a Stable mode that activates FtsY for downstream steps. Importantly, mutational analyses revealed extensive auto-inhibitory mechanisms that prevent free FtsY from engaging membrane in the Stable mode; an engineered FtsY pre-organized into the Stable mode led to indiscriminate targeting in vitro and disrupted FtsY function in vivo. Our results show that the two-step lipid-binding mechanism uncouples the membrane association of FtsY from its conformational activation, thus optimizing the balance between the efficiency and fidelity of co-translational protein targeting.DOI: http://dx.doi.org/10.7554/eLife.25885.001

Specific structural elements of the T-box riboswitch drive the two-step binding of the tRNA ligand

“…Two-step binding mechanisms have been observed in a variety of protein or nucleic acid mediated biological process, including T-cell receptor (TCR) recognition of the major histocompatibility complex (MHC) presenting peptides, where TCRs scan the MHC scaffold first, followed by sensing of specific MHC-presenting peptides ( Wu et al, 2002 ); interaction of the signal recognition particle (SRP) receptor with the membrane, where SRP receptors interact with the membrane in a dynamic mode followed by an SRP-induced conformational transition into a stable binding mode ( Hwang Fu et al, 2017 ), DNA interrogation by CRISPR Cas9-crRNA, where Cas9-crRNA recognizes the protospacer adjacent motif (PAM) on the target DNA followed by sensing of the spacer sequence and triggering R-loop formation ( Sternberg et al, 2014 ); and RNA-induced silencing complexes (RISCs) binding to their mRNA targets, where dynamic sampling of the ‘sub-seed’ region occurs before targeting stably across the full seed region ( Chandradoss et al, 2015 ; Herzog and Ameres, 2015 ; Salomon et al, 2015 ; Salomon et al, 2016 ). In all of these cases, a two-step binding mechanism provides a good balance between sensitivity and specificity.…”

Molecular mechanism of cargo recognition and handover by the mammalian signal recognition particle

“…In addition to the NG domain, Ffh contains a methionine-rich domain (M domain) that recognizes and binds the emerging N-terminal signal sequence or a trans-membrane domain (TMD) of the nascent polypeptide chain on the translating ribosome, referred to as ribosome nascent chain complex (RNC). In addition to the NG domain, FtsY contains an N-terminal A domain with two amphipathic regions that bind the cell membrane and the SecYEG translocation machinery in bacteria ( Draycheva et al, 2016 ; Hwang Fu et al, 2017 ; Park and Rapoport, 2012 ).…”

Direct observation of alpha-lactalbumin, adsorption and incorporation into lipid membrane and formation of lipid/protein hybrid structures

“…The interaction of proteins with cellular membranes controls fundamental cellular processes such as membrane trafficking, cytokinesis, and intracellular signaling [1][2][3][4][5][6][7]. Beside cytoplasmic, peripheral or integral membrane proteins, there is a class of proteins known as amphitropic that interacts with lipids and membranes during their biological activity [8,9].…”