proteins similar to periplasmic molecular chaperone LolA, the outer membrane lipoprotein receptor LolB and the periplasmic protein RseB
This family contains uncharacterized proteins similar to the periplasmic molecular chaperone LolA, the outer membrane lipoprotein receptor LolB and the periplasmic protein RseB, all of which have similar unclosed beta-barrel structures that resemble a baseball glove-like scaffold consisting of an 11-stranded antiparallel sheet. There are five Lol proteins (LolA, LolB, LolC, LolD, and LolE) involved in the sorting and membrane localization of lipoprotein and are highly conserved in Gram-negative bacteria. LolA accepts outer membrane (OM)-specific lipoproteins that are released from the inner membrane by the LolCDE complex and transfers them to the OM receptor LolB. It is proposed that the LolA/LolB complex forms a tunnel-like structure, where the hydrophobic insides of LolA and LolB are connected, which enables lipoproteins to transfer from LolA to LolB. RseB exerts a crucial role in modulating the stability of RseA, the transmembrane anti-sigma-factor that is degraded during sigma-E-dependent transcription caused by bacterial envelope stress. Its structural similarity to LolA and LolB suggests that RseA may act as a sensor of periplasmic stress with a dual functionality, detecting mislocalized lipoproteins as well as propagating the signal to induce the sigma-E-response.