The SurA periplasmic PPIase lacking its parvulin domains functions in vivo and has chaperone activity

The Escherichia coli periplasmic peptidyl‐prolyl isomerase (PPIase) SurA is involved in the maturation of outer membrane porins. SurA consists of a substantial N‐terminal region, two iterative parvulin‐like domains and a C‐terminal tail. Here we show that a variant of SurA lacking both parvulin‐like domains exhibits a PPIase‐independent chaperone‐like activity in vitro and almost completely complements the in vivo function of intact SurA. SurA interacts preferentially (>50‐fold) with in vitro synthesized porins over other similarly sized proteins, leading us to suggest that the chaperone‐like function of SurA preferentially facilitates maturation of outer membrane proteins.