With around 20% of the E. coli proteome destined for the cell envelope, quality control mechanismsĀ are implemented to ensure the effective and correct folding of proteins destined for the inner and outer membranes. These proteins are comprised largely of chaperones and proteases that reside within the periplasm, several of which have been well characterised including SurA, Skp, and DegP to name a few [1]. However, there are more and more cases whereby a specific proteins requires a specific chaperone to support their biogenesis assembly pathway.
The translocase assembly machinery or TAM is a protein complex spanning the bacterial cell envelope and is involved in the assembly of outer membrane secretion systems[2,3]. It is composed of the outer membrane protein, TamA, that adopts a Ī²-barrel fold within the membrane and also contains a periplasmic soluble domain that interacts with its partner protein, TamB. Much less is known about TamB, suffice to say it is a very large (150kDa) periplasmic protein that is anchored to the inner membrane via its N-terminus [2]. Several issues in trying to express these proteins recombinantly lead us to ask what are they key components involved during their biogenesis? Could there be additional periplasmic chaperones or folding partners that are essential to the folding and assembly of TamA and TamB? To address these questions we have applied RNAseq to explore the transcriptomic landscape during the overexpression of TamA and TamB. In doing so we can identify proteins that are up- or down-regulated during TAM protein expression. This will enable us to understand the distinct folding pathways of TamA and TamB and determine if this is a general mechanism for membrane protein biogeneisis or perhaps specific to the TAM.