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Updated: Sep 20, 2026

Site-Specific Lysine Lactylation via Genetic Code Expansion in E. coli and Mammalian Cells
Published on: February 24, 2026
Intermolecular thiol cross-linking via loops in the lactose permease of Escherichia coli
Natalia Ermolova1, Lan Guan, H Ronald Kaback
1Howard Hughes Medical Institute, Department of Physiology and Microbiology, University of California, Los Angeles, CA 90095-1662, USA.
Abstract:
Previous experiments using intermolecular thiol cross-linking to determine surface-exposed positions in the transmembrane helices of the lactose permease suggest that only positions accessible from the aqueous phase are susceptible to cross-linking. This approach is now extended to most of the remaining positions in the molecule. Of an additional 143 single-Cys mutants studied, homodimer formation is observed with both a 5-A- and a 21-A-long crosslinking agent containing bis-methane thiosulfonate reactive groups in 33 mutants and exclusively with the 21-A-long reagent in 43 mutants. Furthermore, intermolecular cross-linking has little or no effect on transport activity, thereby providing further support for the argument that lactose permease is functionally, as well as structurally, a monomer in the membrane. In addition, evidence is presented indicating that reentrance loops are unlikely in this polytopic membrane transport protein.
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