Cancer Center, Renmin Hospital of Wuhan University, Wuhan, China.
Kobilka Institute of Innovative Drug Discovery, School of Medicine, The Chinese University of Hong Kong, Shenzhen, Shenzhen, China.
Nat Commun. 2024 Apr 22;15(1):3404. doi: 10.1038/s41467-024-47783-7.
DltB, a model member of the Membrane-Bound O-AcylTransferase (MBOAT) superfamily, plays a crucial role in D-alanylation of the lipoteichoic acid (LTA), a significant component of the cell wall of gram-positive bacteria. This process stabilizes the cell wall structure, influences bacterial virulence, and modulates the host immune response. Despite its significance, the role of DltB is not well understood. Through biochemical analysis and cryo-EM imaging, we discover that Streptococcus thermophilus DltB forms a homo-tetramer on the cell membrane. We further visualize DltB in an apo form, in complex with DltC, and in complex with its inhibitor amsacrine (m-AMSA). Each tetramer features a central hole. The C-tunnel of each protomer faces the intratetramer interface and provides access to the periphery membrane. Each protomer binds a DltC without changing the tetrameric organization. A phosphatidylglycerol (PG) molecule in the substrate-binding site may serve as an LTA carrier. The inhibitor m-AMSA bound to the L-tunnel of each protomer blocks the active site. The tetrameric organization of DltB provides a scaffold for catalyzing D-alanyl transfer and regulating the channel opening and closing. Our findings unveil DltB's dual function in the D-alanylation pathway, and provide insight for targeting DltB as a anti-virulence antibiotic.
DltB 是膜结合 O-酰基转移酶（MBOAT）超家族的典型成员，在 D-丙氨酸化脂磷壁酸（LTA）中发挥关键作用，LTA 是革兰氏阳性菌细胞壁的重要组成部分。该过程稳定细胞壁结构、影响细菌毒力，并调节宿主免疫反应。尽管 DltB 意义重大，但它的作用尚未完全了解。通过生化分析和冷冻电镜成像，我们发现嗜热链球菌 DltB 在细胞膜上形成同源四聚体。我们进一步可视化了 DltB 的apo 形式、与 DltC 的复合物形式，以及与抑制剂安丝菌素 m-AMSA（m-AMSA）的复合物形式。每个四聚体都有一个中央孔。每个原体的 C-隧道面向内部分子间界面，提供了通往外周膜的通道。每个原体都结合一个 DltC，而不改变四聚体的组织形式。底物结合位点中的一个磷脂酰甘油（PG）分子可能作为 LTA 载体。抑制剂 m-AMSA 结合到每个原体的 L-隧道中，从而阻断了活性位点。DltB 的四聚体组织为催化 D-丙氨酸转移和调节通道开启和关闭提供了支架。我们的研究结果揭示了 DltB 在 D-丙氨酸化途径中的双重功能，并为将 DltB 作为抗毒力抗生素作为靶点提供了新的见解。
