A highly efficient protein photo‐cross‐linking probe reveals a unique chaperone‐chaperone protection mechanism

We report the development of a highly efficient photo‐cross‐linking probe which allowed us to identify a novel protective function of an acid‐stress chaperone HdeA on the major protein quality control factor, SurA, in the biogenesis of bacterial outer membrane proteins (Fig. 1a). We inserted the synthesized photo‐cross‐linker DiZPK (3‐(3‐methyl‐3H‐diazirin‐3‐yl)‐propamino‐carbonyl‐Nε‐L‐Lysine) into both hydrophobic and hydrophilic regions of HdeA trying to capture proteins interacting with HdeA in living cells (Fig. 1b, c). By using mass spectrometry analysis, nine proteins were identified, among which the molecular chaperone SurA has the highest identification score. Then we demonstrated HdeA strongly suppresses SurA aggregation under low pH and might facilitate the recovery of SurA upon subsequent pH neutralization with both in vitro and in vivo experiments. Such a unique chaperone‐chaperone protection mechanism might be a fairly effective strategy employed by enteric bacteria to maintain the integrity of a much broader range of proteins when passing through the extremely acidic mammalian stomachs. This work was supported by research grants from the National Key Basic Research Foundation of China (2010CB912300 to P.R.C.; 2006CB806508 and 2006CB910300 to Z.Y.C.).