Researchers have determined the cryo-EM structures of the noncanonical LolDF transport complex in Acinetobacter baylyi, according to a study published in Nature Communications. Lipoprotein trafficking is essential for Gram-negative bacteria to maintain the outer membrane, which functions as a permeability barrier for survival and antibiotic resistance.
While most Gram-negative bacteria use the canonical LolCDE transporter, Acinetobacter relies on the LolDF system. The research team solved structures of LolDF in three separate conformations: substrate-bound, AMP-PNP-bound, and LolA-bound states. The structural data show that LolDF forms a symmetric homodimer with a central cavity that accommodates three acyl chains at the membrane level, pointing to lateral extraction of lipoproteins directly from the inner membrane.
AMP-PNP-driven conformational changes cause a coordinated symmetric constriction of the central cavity that drives substrate expulsion. This symmetric action differs from the asymmetric mechanism previously observed in LolCDE transporters.
Functional experiments identified specific door-bar residues required for transport activity. The authors also found that charged residues at the +3 position operate as an inner membrane retention signal in the bacterium.
The study was led by co-first authors Jie Pang, Yawen Chen, Wen Qiao, and Zijing Ju across institutions including West China Hospital at Sichuan University, the Chinese Academy of Sciences, Southern Medical University, and Zhejiang University School of Medicine. Project funding included grants from the National Key Research and Development Program of China and the National Natural Science Foundation of China.
