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Cai X, Liu L, Qiu C, Wen C, He Y, Cui Y, Li S, Zhang X, Zhang L, Tian C, Bi L, Zhou ZH, Gong W. Identification and architecture of a putative secretion tube across mycobacterial outer envelope. SCIENCE ADVANCES 2021; 7:7/34/eabg5656. [PMID: 34417177 PMCID: PMC8378821 DOI: 10.1126/sciadv.abg5656] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/16/2021] [Accepted: 06/29/2021] [Indexed: 06/13/2023]
Abstract
Tuberculosis-causing mycobacteria have thick cell-wall and capsule layers that are formed from complex structures. Protein secretion across these barriers depends on a specialized protein secretion system, but none has been reported. We show that Mycobacterium tuberculosis Rv3705c and its homologous MSMEG_6251 in Mycobacterium smegmatis are tube-forming proteins in the mycobacterial envelope (TiME). Crystallographic and cryo-EM structures of these two proteins show that both proteins form rotationally symmetric rings. Two layers of TiME rings pack together in a tail-to-tail manner into a ring-shaped complex, which, in turn, stacks together to form tubes. M. smegmatis TiME was detected mainly in the cell wall and capsule. Knocking out the TiME gene markedly decreased the amount of secreted protein in the M. smegmatis culture medium, and expression of this gene in knocked-out strain partially restored the level of secreted protein. Our structure and functional data thus suggest that TiME forms a protein transport tube across the mycobacterial outer envelope.
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Affiliation(s)
- Xiaoying Cai
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Lei Liu
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui, China
| | - Chunhong Qiu
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Chongzheng Wen
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui, China
| | - Yao He
- California NanoSystems Institute, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
- Department of Microbiology, Immunology and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA
| | - Yanxiang Cui
- California NanoSystems Institute, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
| | - Siyu Li
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Xuan Zhang
- Institute of Health Science, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, China
| | - Longhua Zhang
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Changlin Tian
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Lijun Bi
- Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Z Hong Zhou
- California NanoSystems Institute, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA.
- Department of Microbiology, Immunology and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA
| | - Weimin Gong
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China.
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui, China
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