Structural insights into terminal arabinosylation of mycobacterial cell wall arabinan

• Published in: Nature communications Vol. 16; no. 1; pp. 3973 - 16
• Main Authors: Liu, Yaqi, Brown, Chelsea M., Erramilli, Satchal, Su, Yi-Chia, Guu, Shih-Yun, Tseng, Po-Sen, Wang, Yu-Jen, Duong, Nam Ha, Tokarz, Piotr, Kloss, Brian, Han, Cheng-Ruei, Chen, Hung-Yu, Rodrigues, José, Khoo, Kay-Hooi, Archer, Margarida, Kossiakoff, Anthony A., Lowary, Todd L., Stansfeld, Phillip J., Nygaard, Rie, Mancia, Filippo
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29.04.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 101/28; 631/326/41/2536; 631/45/173; 631/535/1258/1259; 82/80; 82/83; Arabinogalactan; Arabinose; Arabinose - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Binding sites; Biosynthesis; Cell Wall - chemistry; Cell Wall - metabolism; Cell walls; Cryoelectron Microscopy; Drug resistance; Galactans - metabolism; Helices; Humanities and Social Sciences; Lipopolysaccharides - chemistry; Lipopolysaccharides - metabolism; Models, Molecular; Molecular dynamics; multidisciplinary; Mycobacterium - metabolism; Mycobacterium tuberculosis - metabolism; Pathogenicity; Pentosyltransferases - chemistry; Pentosyltransferases - genetics; Pentosyltransferases - metabolism; Polysaccharides; Polysaccharides - chemistry; Polysaccharides - metabolism; Reaction mechanisms; Residues; Saccharides; Science; Science (multidisciplinary); Structural analysis; Structure-function relationships; Tuberculosis
• DOI: 10.1038/s41467-025-58196-5
• ISSN: 2041-1723

The global challenge of tuberculosis, caused by Mycobacterium tuberculosis (Mtb) , is compounded by the emergence of drug-resistant strains. A critical factor in Mtb ’s pathogenicity is its intricate cell envelope, which acts as a formidable barrier against immune defences and pharmacological interventions. Central to this envelope are arabinogalactan (AG) and lipoarabinomannan (LAM), two complex polysaccharides containing arabinan domains essential for maintaining cell wall structure and function. The arabinofuranosyltransferase AftB plays a pivotal role in the biosynthesis of these arabinan domains by catalyzing the addition of β-(1 → 2)-linked terminal arabinofuranose residues. Here, we present the cryo-EM structures of Mycobacterium chubuense AftB in both its apo form and bound to a donor substrate analog, resolved at 2.9 Å and 3.4 Å resolution, respectively. These structures reveal that AftB has a GT-C fold, with a transmembrane (TM) domain comprised of eleven TM helices and a periplasmic cap domain. AftB has a distinctive irregular, tube-shaped cavity that connects two proposed substrate binding sites. Through an integrated approach combining structural analysis, biochemical assays, and molecular dynamics simulations, we delineate the molecular basis of AftB’s reaction mechanism and propose a model for its catalytic function. Here, the authors present cryoEM structures of AftB, a key mycobacterial enzyme that adds terminal arabinose residues to the cell wall. In concert with functional assays and MD simulations, mechanistic insights are presented.