Myxococcus xanthus encapsulin cargo protein EncD is a flavin- binding protein with ferric reductase activity

• 成果类型: Article
• 署名作者: Eren, Elif; Watts, Norman R.; Conway, James F.; Wingfield, Paul T.
• 署名单位: National Institutes of Health (NIH) - USA; NIH National Institute of Arthritis & Musculoskeletal & Skin Diseases (NIAMS); Pennsylvania Commonwealth System of Higher Education (PCSHE); University of Pittsburgh
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11376
• DOI: 10.1073/pnas.2400426121
• 发表日期: 2024-05-21
• 关键词: rhodococcus-jostii rha1; escherichia-coli; iron; nanocompartment; identification; peroxidase; flavodoxin; particle; dypb

摘要

Encapsulins are protein nanocompartments that regulate cellular metabolism in several bacteria and archaea. Myxococcus xanthus encapsulins protect the bacterial cells against oxidative stress by sequestering cytosolic iron. These encapsulins are formed by the shell protein EncA and three cargo proteins: EncB, EncC, and EncD. EncB and EncC form rotationally symmetric decamers with ferroxidase centers (FOCs) that oxidize Fe +2 to Fe +3 for iron storage in mineral form. However, the structure and function of the third cargo protein, EncD, have yet to be determined. Here, we report the x - ray crystal structure of EncD in complex with flavin mononucleotide. EncD forms an alpha- helical hairpin arranged as an antiparallel dimer, but unlike other flavin - binding proteins, it has no beta- sheet, showing that EncD and its homologs represent a unique class of bacterial flavin - binding proteins. The cryo - EM structure of EncA - EncD encapsulins confirms that EncD binds to the interior of the EncA shell via its C - terminal targeting peptide. With only 100 amino acids, the EncD alpha- helical dimer forms the smallest flavin - binding domain observed to date. Unlike EncB and EncC, EncD lacks a FOC, and our biochemical results show that EncD instead is a NAD(P)H - dependent ferric reductase, indicating that the M. xanthus encapsulins act as an integrated system for iron homeostasis. Overall, this work contributes to our understanding of bacterial metabolism and could lead to the development of technologies for iron biomineralization and the production of iron - containing materials for the treatment of various diseases associated with oxidative stress.