Structural basis for iterative methylation by a cobalamin-dependent radical S-adenosylmethionine enzyme in cystobactamids biosynthesis

• 成果类型: Article
• 署名作者: Cui, Jiayuan; Wang, Bo; Maurya, Ravi K.; Booker, Squire J.
• 署名单位: Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Pennsylvania; Howard Hughes Medical Institute; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Pennsylvania; Pennsylvania Medicine
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2527019123
• 发表日期: 2026-01-27
• 页码: e2527019123
• 关键词: radical S-adenosylmethionine; iterative methylation; crystallography; COBALAMIN; cystobactamids; SAM ENZYME; MODEL

摘要

Cystobactamids are nonribosomal peptide natural products that function as DNA gyrase inhibitors, exhibiting significant antibacterial activity. They are isolated from Cystobacter sp. Cbv34 and contain various alkoxy groups on para-aminobenzoic acid moieties, which are believed to play a crucial role in antibacterial functions. The alkoxy groups are generated by iterative methylations on a methoxy group by the cobalamin to three methylations to give ethoxy, isopropoxy, sec-butoxy, and tert-butoxy groups. For each methylation, CysS uses a ping-pong mechanism in which two molecules of SAM are consumed. One SAM is used to methylate cob(I)alamin, while another generates a 5 '-deoxyadenosyl 5 '-radical to initiate substrate methylation. However, little is known about how the enzyme promotes both Cbl methylation and iterative substrate methylation, which occur by polar SN2 and radical processes, respectively. Here, we report three X-ray crystal structures of a homolog of CysS from Corallococcus sp. CA054B. Two were determined in the presence of methoxy- and ethoxy-containing substrates, showing how CysS accommodates substrates and products during iterative methylation. The third structure, determined in the absence of a substrate, exhibits structural changes that reorient the SAM's conformation to allow for the methylation of cob(I)alamin.