The Helix Rearrangement in the Periplasmic Domain of the Flagellar Stator B Subunit Activates Peptidoglycan Binding and Ion Influx

• Published in: Structure (London) Vol. 26; no. 4; pp. 590 - 598.e5
• Main Authors: Kojima, Seiji, Takao, Masato, Almira, Gaby, Kawahara, Ikumi, Sakuma, Mayuko, Homma, Michio, Kojima, Chojiro, Imada, Katsumi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 03.04.2018
• Subjects: Amino Acid Motifs; Amino Acid Substitution; bacterial flagellum; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Binding Sites; Cloning, Molecular; crystal structure; Crystallography, X-Ray; Escherichia coli - genetics; Escherichia coli - metabolism; Flagella - chemistry; Flagella - metabolism; Gene Expression; Genetic Vectors - chemistry; Genetic Vectors - metabolism; Ion Transport; Models, Molecular; motility; Mutation; peptidoglycan; Peptidoglycan - chemistry; Peptidoglycan - metabolism; Periplasm - chemistry; Periplasm - metabolism; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Protein Multimerization; proton-driven motor; Protons; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Salmonella enterica - chemistry; Salmonella enterica - metabolism; solution NMR; stator; bacterial flagellum; peptidoglycan; proton-driven motor; crystal structure; motility; stator; solution NMR
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2018.02.016

The stator of the bacterial flagellar motor couples ion flow with torque generation. The ion-conducting stator channel opens only when incorporated into and anchored around the rotor via the peptidoglycan (PG) binding domain of the B subunit (MotBC). However, no direct evidence of PG binding coupled with channel activation has been presented. Here, we report the structural rearrangements of MotBC responsible for this coupling process. A MotBC fragment with the L119P replacement, which is known to cause channel activation, was able to bind PG. Nuclear magnetic resonance analysis of MotBC and the crystal structure of the MotBC-L119P dimer revealed major structural changes in helix α1. In vivo crosslinking results confirm that a major rearrangement occurs. Our results suggest that, upon stator incorporation into the motor, helix α1 of MotBC changes into an extended non-helical structure. We propose that this change allows the stator both to bind PG and to open its proton channel. [Display omitted] •The stator of the flagellar motor couples ion flow with torque generation•The stator channel opens upon incorporation into the motor, anchoring to the PG layer•L119P replacement in MotB induces an active conformation of stator that can bind PG•A dynamic helix rearrangement in the PG-binding domain of MotB occurs upon activation Kojima et al. provide direct evidence for coupling between peptidoglycan (PG)-binding and activation of the flagellar stator protein. Using X-ray and NMR analyses they reveal that dynamic rearrangement of the N-terminal helix of the PG-binding domain of the stator protein MotB is key for its functional activation and energy conversion.