This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Gram-negative bacteria are responsible for several infections that are hard to treat because of their high resistance to antibiotics. These bacteria possess an outermost layer called the outer membrane that acts as a protective barrier.
Serving as the cell's interface with the outside world, the outer membrane contains specialized proteins that perform multiple functions, such as nutrient transport and environmental sensing. The localization of these outer membrane proteins is achieved through the combined action of several key players, including the SurA chaperone and the β-barrel assembly machinery (BAM) complex. SurA acts as a periplasmic chaperone that binds unfolded outer membrane proteins (OMPs) and delivers them to BAM, where they are correctly folded and inserted into the outer membrane.
Although many aspects of BAM-mediated OMP assembly are well understood, how SurA physically transfers its OMP cargo to BAM remains unclear. In a recent study, a research team led by Assistant Professor Ryoji Miyazaki from Nara Institute of Science and Technology (NAIST), Japan, set out to fill this knowledge gap. Their work, which will be published in Nature Communications on Sept. 4, 2026, reveals that SurA adopts multiple conformations while associated with BAM and identifies interactions that may help move its OMP cargo toward the assembly machinery.
The paper was co-authored by Assistant Professor Hidetaka Kohga, Nami Matsuoka, Wataru Yoshimoto, Yutaro S. Takahashi, and Professor Tomoya Tsukazaki from NAIST; Yuki Maruno and Associate Professor Takuya Shiota from the University of Miyazaki, Japan; Dr. Dede Heri Yuli Yanto and Dr.
Yudhi Nugraha from the National Research and Innovation Agency, Indonesia; and Dr. Hideki Shigematsu from the Japan Synchrotron Radiation Research Institute, Japan. The researchers used cryo-electron microscopy (cryo-EM) to visualize the SurA–BAM complex.
Cryo-EM analysis revealed two distinct structures in which either the SurA Core domain alone or the Core and P1 domains were resolved. Because the flexible P2 domain remained unresolved, the researchers introduced specific mutations in SurA to create disulfide bonds at carefully calculated positions between SurA and BAM, stabilizing particular conformations for structural analysis. This approach enabled the team to capture four distinct structural snapshots of SurA bound to BAM (Core-only, P1-visible, P2-visible, and P1/P2-visible), illustrating how SurA reconfigures itself to assist with OMP delivery.
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