An alternate mode of oligomerization for E. coli SecA

• Published in: Scientific reports Vol. 7; no. 1; pp. 11747 - 17
• Main Authors: Yazdi, Aliakbar Khalili, Vezina, Grant C., Shilton, Brian H.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18-09-2017; Nature Publishing Group
• Subjects: 631/45/535/1261; 631/45/535/1266; 631/80/2023/2022; 631/80/470/1981; 82/80; 82/83; Adenosine triphosphatase; Adenosine Triphosphatases - chemistry; Adenosine Triphosphatases - genetics; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; BASIC BIOLOGICAL SCIENCES; Chaperones; Crystallography, X-Ray; Crystals; E coli; Escherichia coli - enzymology; Escherichia coli - genetics; Humanities and Social Sciences; Monomers; multidisciplinary; N-Terminus; Oligomerization; Preprotein translocase; Protein Domains; Protein Multimerization; Protein Structure, Quaternary; Protein translocation; SAXS; Science; Science (multidisciplinary); SEC Translocation Channels - chemistry; SEC Translocation Channels - genetics; SecA Proteins; Translocase; Translocation; X-ray crystallography; X-ray scattering
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-11648-5

SecA is the ATPase of preprotein translocase. SecA is a dimer in solution and changes in its oligomeric state may function in preprotein translocation. The SecA-N68 construct, in which the C-terminal helical domains of SecA are deleted, was used to investigate the mechanism of SecA oligomerization. SecA-N68 is in equilibrium between monomers, dimers, and tetramers. Subunit interactions in the SecA-N68 tetramer are mediated entirely by unstructured regions at its N- and C-termini: when the termini are deleted to yield SecA-N68∆NC, the construct is completely monomeric. This monomeric construct yielded crystals diffracting to 2.6 Å that were used to solve the structure of SecA-N68, including the “preprotein crosslinking domain” (PPXD) that was missing from previous
E. coli
SecA structures. The SecA-N68 structure was combined with small angle X-ray scattering (SAXS) data to construct a model of the SecA-N68 tetramer that is consistent with the essential roles of the extreme N- and C-termini in oligomerization. This mode of oligomerization, which depends on binding of the extreme N-terminus to the DEAD motor domains, NBD1 and NBD2, was used to model a novel parallel and flexible SecA solution dimer that agrees well with SAXS data.