Architecture of the major component of the type III secretion system export apparatus

• Published in: Nature structural & molecular biology Vol. 20; no. 1; pp. 99 - 104
• Main Authors: Abrusci, Patrizia, Vergara-Irigaray, Marta, Johnson, Steven, Beeby, Morgan D, Hendrixson, David R, Roversi, Pietro, Friede, Miriam E, Deane, Janet E, Jensen, Grant J, Tang, Christoph M, Lea, Susan M
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.01.2013; Nature Publishing Group
• Subjects: 631/326/41/1969/2180; 631/535; Amino Acid Sequence; Bacteria; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - metabolism; Bacterial Secretion Systems; Biochemistry; Biological Microscopy; Biological Transport; Cell Membrane - metabolism; Cell membranes; Life Sciences; Membrane Biology; Membranes; Models, Molecular; Molecular biology; Molecular Sequence Data; Molecular structure; Physiological aspects; Properties; Protein Conformation; Protein Structure; Protein Structure, Secondary; Proteins; Secretion; Shigella flexneri; Shigella flexneri - enzymology; Shigella flexneri - metabolism; United States; United Kingdom
• ISSN: 1545-9993; 1545-9985
• DOI: 10.1038/nsmb.2452

The transmembrane export apparatus regulates protein secretion through bacterial type III secretion systems. New structural data indicate that MxiA, a major component of the apparatus, assembles in a nonameric ring. This and additional structural information provide a framework for understanding how protein secretion is controlled. Type III secretion systems (T3SSs) are bacterial membrane–embedded nanomachines designed to export specifically targeted proteins from the bacterial cytoplasm. Secretion through T3SS is governed by a subset of inner membrane proteins termed the 'export apparatus'. We show that a key member of the Shigella flexneri export apparatus, MxiA, assembles into a ring essential for secretion in vivo . The ring-forming interfaces are well-conserved in both nonflagellar and flagellar homologs, implying that the ring is an evolutionarily conserved feature in these systems. Electron cryo-tomography revealed a T3SS-associated cytoplasmic torus of size and shape corresponding to those of the MxiA ring aligned to the secretion channel located between the secretion pore and the ATPase complex. This defines the molecular architecture of the dominant component of the export apparatus and allows us to propose a model for the molecular mechanisms controlling secretion.