Membrane Chaperones: A Folding–Stability–Function Tug-of-War?

β-Barrel outer membrane proteins (OMPs) are unique to Gram-negative bacteria and mitochondria. All OMPs require the Barrel Assembly Machinery (BAM) (bacteria), and Sorting and Assembly Machinery (SAM) (mitochondria), with BamA and Sam50 being their core chaperones (1). Despite their indispensable role, we know little about both proteins. Here, we obtain a complete molecular map of regulatory elements for both BamA and Sam50, by combining ultrafast measurements of their stepwise molecular (un)folding in native-like membranes, with end-state thermodynamics, and single–molecule functional studies (2). We establish how both BamA and Sam50 evolved conformational buffering of sequence–guided structure–function handles for superior OMP biogenesis and BAM/SAM interactome in vivo. Our findings open avenues for developing designed peptidomimetics as highly effective next-generation therapeutics.