Dynamic interplay between the periplasmic and transmembrane domains of GspL and GspM in the type II secretion system

• Published in: PloS one 2013-11, Vol.8 (11), p.e79562
• Main Authors: Lallemand, Mathilde, Login, Frédéric H, Guschinskaya, Natalia, Pineau, Camille, Effantin, Géraldine, Robert, Xavier, Shevchik, Vladimir E
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Secretion Systems; Bioinformatics; Cell Membrane - metabolism; Chemical bonds; E coli; Ecology, environment; Enterobacteriaceae - cytology; Erwinia chrysanthemi; Escherichia coli; Ferredoxin; Ferredoxins - chemistry; Genetic aspects; Gram-negative bacteria; Interfaces; Laboratories; Life Sciences; Membrane proteins; Microbiology and Parasitology; Models, Molecular; Molecular modelling; Molecular Sequence Data; Mutagenesis; Pathogens; Periplasm - metabolism; Physiological aspects; Protein Binding; Protein Multimerization; Protein Structure, Quaternary; Protein Structure, Tertiary; Proteins; Secretion; Signal transduction; Signal transmission; Symbiosis; Transmembrane domains
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0079562

The type II secretion system (T2SS) is a multiprotein nanomachine that transports folded proteins across the outer membrane of gram-negative bacteria. The molecular mechanisms that govern the secretion process remain poorly understood. The inner membrane components GspC, GspL and GspM possess a single transmembrane segment (TMS) and a large periplasmic region and they are thought to form a platform of unknown function. Here, using two-hybrid and pull-down assays we performed a systematic mapping of the GspC/GspL/GspM interaction regions in the plant pathogen Dickeya dadantii. We found that the TMS of these components interact with each other, implying a complex interaction network within the inner membrane. We also showed that the periplasmic, ferredoxin-like, domains of GspL and GspM drive homo- and heterodimerizations of these proteins. Disulfide bonding analyses revealed that the respective domain interfaces include the equivalent secondary-structure elements, suggesting alternating interactions of the periplasmic domains, L/L and M/M versus L/M. Finally, we found that displacements of the periplasmic GspM domain mediate coordinated shifts or rotations of the cognate TMS. These data suggest a plausible mechanism for signal transmission between the periplasmic and the cytoplasmic portions of the T2SS machine.