60 kDa inner membrane protein, YidC (involved in insertion of a wide range of membrane proteins, including the c-subunit of the F-type ATPase (van der Laan et al. 2004) and the anaerobic respiratory complexes (Price and Driessen, 2008). The thrid TMS in YidC contacts the substrate protein (Yu et al., 2008).  YidC occupies the lateral gate of the SecYEG translocase and is sequentially displaced by the nascent membrane protein (Sachelaru et al. 2013).  Residues involved in interaction with the Sec translocon have been identified (Li et al. 2014). YidC acts as a flexible chaperone, facilitating LacY folding (Zhu et al. 2013; Hennon and Dalbey 2014).  The structure of the dimeric insertion pore associated with the translating ribosome has been solved (Kohler et al. 2009).  A single copy of YidC interacts with the ribosome at the ribosomal tunnel; a site for membrane protein insertion at the YidC protein-lipid interface has been identified (Wickles et al. 2014).  The crystal structure of full-length E. coli YidC revealed that a hydrophilic groove, formed by five transmembrane helices, is a conserved structural feature as compared to the previous YidC structure from Bacillus halodurans, which lacks a periplasmic domain. Structural mapping of the substrate- or Sec protein-contact sites suggested the importance of the groove for the YidC functions as a chaperone and an insertase (Kumazaki et al. 2014). Pf3 is inserted as a helical hairpin, i.e., the prospective TMS moves along the YidC greasy slide comprised of TMS3 and TMS5, whereas the N-terminal tail transiently folds back into the hydrophilic groove of YidC located in the inner leaflet of the membrane until it is translocated to the periplasm in a subsequent step involving the pmf (Hennon and Dalbey 2014).  The structure of the dimeric insertion pore associated with the translating ribosome has been solved (Kohler et al. 2009).  A single copy of YidC interacts with the ribosome at the ribosomal tunnel; a site for membrane protein insertion at the YidC protein-lipid interface has been identified (Wickles et al. 2014).  The crystal structure of full-length E. coli YidC revealed that a hydrophilic groove, formed by five transmembrane helices, is a conserved structural feature as compared to the previous YidC structure from Bacillus halodurans, which lacks a periplasmic domain. Structural mapping of the substrate- or Sec protein-contact sites suggested the importance of the groove for the YidC functions as a chaperone and an insertase (Kumazaki et al. 2014). Pf3 is inserted as a helical hairpin, i.e., the prospective TMS moves along the YidC greasy slide comprised of TMS3 and TMS5, whereas the N-terminal tail transiently folds back into the hydrophilic groove of YidC located in the inner leaflet of the membrane until it is translocated to the periplasm in a subsequent step involving the pmf (He et al. 2020).