Updated project metadata. The SecYEG translocon constitutes the major protein transporting channel in bacteria and transports an enormous variety of different secretory and inner membrane proteins. The minimal core of the SecYEG translocon consists of the three inner membrane proteins SecY, SecE and SecG, which together with appropriate targeting factors are sufficient for protein transport in vitro. However, in vivo the SecYEG translocon has been shown to associate with multiple partner proteins, which likely allow the SecYEG translocon to manage diverse substrates. For obtaining a global view on SecYEG plasticity, a label free proteomics approach was executed, which identified known SecYEG interacting proteins, verified the interaction with quality control proteins and identified several novel putative SecYEG interactors. Surprisingly, the chaperone complex PpiD/YfgM was identified as the most pronounced contact partner of SecYEG and was much dominant than the established partner protein YidC. Detailed analyses of the PpiD and YidC contact sites on SecY by site directed cross-linking revealed that PpiD and YidC use almost completely overlapping binding sites on SecY and contact the lateral gate, the plug domain and the periplasmic cavity of SecY. Still, despite having almost identical binding sites, their binding to SecY is non-competitive as determined by quantitative mass spectrometry and cross-linking. This implies that the SecYEG translocon forms different substrate-independent sub-assemblies, in which SecYEG is either in contact with YidC or with the PpiD/YfgM complex.