Genetic analysis defines sites of charge-based interaction between LolA and LolB proteins in lipoprotein trafficking

Charge-based interactions between Escherichia coli LolA and LolB are defined by essential LolB residues R34, K45, and R49, where charge reversal is lethal.

• Why it matters: The Lol pathway transfers lipoproteins from the inner membrane to the outer membrane, but the molecular basis of LolB function and its interaction with LolA is unclear.
• What they did: A library of single amino acid substitutions across the mature Escherichia coli LolB sequence was screened for severely hypomorphic alleles, validated using a C-terminal truncation and a lipidated cysteine substitution.
• The result: Loss of positive charge at R49 impaired growth, while charge reversal at R49, R34, and K45 was lethal; each lethality was suppressed by reciprocal charge reversals in LolA at E34, D55, and E74.