YrhB is a highly stable small protein with unique chaperone-like activity in Escherichia coli BL21(DE3)

Escherichia coli YrhB (10.6 kDa) from strain BL21(DE3) that is commonly used for protein overexpression is a stable chaperone-like protein and indispensable for supporting the growth of BL21(DE3) at 48 °C but not defined as conventional heat shock protein (HSP). YrhB effectively prevented heat-induced aggregation of ribonucleotide synthetase (PurK). Without ATP, YrhB alone promoted in vitro refolding of uridine phosphorylase (UDP) and protected thermal denaturation of the refolded UDP. As a cis-acting fusion partner, YrhB also significantly reduced inclusion body formation of nine aggregation-prone heterologous proteins in BL21(DE3). Unlike conventional small HSPs, YrhB remained monomer under heat shock condition.

► Escherichia coli small hypothetical protein, YrhB is a small and highly stable protein with a unique chaperone-like function. ► It is indispensable for supporting cell growth of E. coli BL21(DE3) at elevated temperature. ► YrhB shows a high thermal and pH stability. ► YrhB also enhances the protein folding and protects proteins against in vitro or in vivo aggregation and denaturation.