Journal Article Tunnel Formation Inferred from the I-Form Structures of the Proton-Driven Protein Secretion Motor SecDF

Furukawa, Arata  ,  Yoshikaie, Kunihito  ,  Mori, Takaharu  ,  Mori, Hiroyuki  ,  Morimoto, Yusuke V  ,  Sugano, Yasunori  ,  Iwaki, Shigehiro  ,  Minamino, Tohru  ,  Sugita, Yuji  ,  Tanaka, Yoshiki  ,  Tsukazaki, Tomoya

2017-05-02 , Cell Press
Protein secretion mediated by SecYEG translocon and SecA ATPase is enhanced by membrane-embedded SecDF by using proton motive force. A previous structural study of SecDF indicated that it comprises 12 transmembrane helices that can conduct protons and three periplasmic domains, which form at least two characterized transition states, termed the F and I forms. We report the structures of full-length SecDF in I form at 2.6- to 2.8-A resolution. The structures revealed that SecDF in I form can generate a tunnel that penetrates the transmembrane region and functions as a proton pathway regulated by a conserved Asp residue of the transmembrane region. In one crystal structure, periplasmic cavity interacts with a molecule, potentially polyethylene glycol, which may mimic a substrate peptide. This study provides structural insights into the Sec protein translocation that allows future analyses to develop a more detailed working model for SecDF.

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