| Popis: |
The outer-membrane of Gram-negative bacteria is critical for surface adhesion, pathogenicity, antibiotic resistance and survival. The major constituents –hydrophobic β-barrel O uter- M embrane P roteins (OMPs)– first need to secreted across the inner-membrane by the Sectranslocon. Following their emergence from the protein-channel in the periplasm, chaperones such as SurA and Skp pick up the cargo to prevent aggregation. The chaperoned OMPs are somehow then delivery through the P eptido- G lycan layer (PG) to the β- B arrel A ssembly M achinery (BAM), where insertion and folding into the outer-membrane occurs. It is very unclear how vast quantities of protein, required for rapid cell wall biogenesis, are trafficked to the outer-membrane while avoiding aggregation, and in the absence of energy. Here, we present in vitro and in vivo biochemical analyses, supported by electron microscopy, to show the H olo- T rans L ocon (HTL; a complex of the core-translocon SecYEG with the accessory proteins SecDF-YajC, and the membrane protein ‘insertase’ YidC) contacts the periplasmic chaperone SurA, and BAM of the outer-membrane. The interaction bestows a new role for the ancillary sub-complex SecDF, which contacts BAM via their extended periplasmic domains. The connection provides a contiguous pathway between the inner- and outer-membrane; for safe and efficient passage of unfolded β-barrel proteins directly to the surface. This inter-membrane conduit would prevent aggregation, and possibly even facilitate energy-transduction from the inner-membrane, conferred by SecDF, for outer-membrane protein insertion and folding. This interaction also provides specific new insight of trans-membrane organisation and communication; an area of increasing biological interest and significance. |
