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The mechanism of protein export enhancement by the SecDF membrane component

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ABSTRACT

Protein transport across membranes is a fundamental and essential cellular activity in all organisms. In bacteria, protein export across the cytoplasmic membrane, driven by dynamic interplays between the protein-conducting SecYEG channel (Sec translocon) and the SecA ATPase, is enhanced by the proton motive force (PMF) and a membrane-integrated Sec component, SecDF. However, the structure and function of SecDF have remained unclear. We solved the first crystal structure of SecDF, consisting of a pseudo-symmetrical 12-helix transmembrane domain and two protruding periplasmic domains. Based on the structural features, we proposed that SecDF functions as a membrane-integrated chaperone, which drives protein movement without using the major energetic currency, ATP, but with remarkable cycles of conformational changes, powered by the proton gradient across the membrane. By a series of biochemical and biophysical approaches, several functionally important residues in the transmembrane region have been identified and our model of the SecDF function has been verified.

No MeSH data available.


Related in: MedlinePlus

Crystal structure of SecDF. SecDF consists of a pseudosymmetrical 12-helix transmembrane domain (TM) and two protruding periplasmic domains (P1 and P4).
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f2-7_129: Crystal structure of SecDF. SecDF consists of a pseudosymmetrical 12-helix transmembrane domain (TM) and two protruding periplasmic domains (P1 and P4).

Mentions: The crystal structure of full-length SecDF, consisting of a 12-helix transmembrane domain and two protruding periplasmic domains, the P1 and P4 domains, was determined at 3.3Å resolution by a single-wavelength anomalous dispersion analysis (Fig. 2; PDB ID 3AQP). TM1–6 and TM7–12 are assembled pseudo-symmetrically. The periplasmic surface of the TM regions is covered by an anti-parallel β-sheet, which is formed by eight-strands of the P1 and P4 domains. The P1 domain is divided into head and base subdomains. The P4 domain is structurally homologous to the P1 base subdomain, and both are assembled in a pseudosymmetrical manner similar to that of the TM region. The characteristic P1 head domain protrudes into the periplasmic space, while the two loops connecting the head and base subdomains form a constricted region.


The mechanism of protein export enhancement by the SecDF membrane component
Crystal structure of SecDF. SecDF consists of a pseudosymmetrical 12-helix transmembrane domain (TM) and two protruding periplasmic domains (P1 and P4).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5036778&req=5

f2-7_129: Crystal structure of SecDF. SecDF consists of a pseudosymmetrical 12-helix transmembrane domain (TM) and two protruding periplasmic domains (P1 and P4).
Mentions: The crystal structure of full-length SecDF, consisting of a 12-helix transmembrane domain and two protruding periplasmic domains, the P1 and P4 domains, was determined at 3.3Å resolution by a single-wavelength anomalous dispersion analysis (Fig. 2; PDB ID 3AQP). TM1–6 and TM7–12 are assembled pseudo-symmetrically. The periplasmic surface of the TM regions is covered by an anti-parallel β-sheet, which is formed by eight-strands of the P1 and P4 domains. The P1 domain is divided into head and base subdomains. The P4 domain is structurally homologous to the P1 base subdomain, and both are assembled in a pseudosymmetrical manner similar to that of the TM region. The characteristic P1 head domain protrudes into the periplasmic space, while the two loops connecting the head and base subdomains form a constricted region.

View Article: PubMed Central - PubMed

ABSTRACT

Protein transport across membranes is a fundamental and essential cellular activity in all organisms. In bacteria, protein export across the cytoplasmic membrane, driven by dynamic interplays between the protein-conducting SecYEG channel (Sec translocon) and the SecA ATPase, is enhanced by the proton motive force (PMF) and a membrane-integrated Sec component, SecDF. However, the structure and function of SecDF have remained unclear. We solved the first crystal structure of SecDF, consisting of a pseudo-symmetrical 12-helix transmembrane domain and two protruding periplasmic domains. Based on the structural features, we proposed that SecDF functions as a membrane-integrated chaperone, which drives protein movement without using the major energetic currency, ATP, but with remarkable cycles of conformational changes, powered by the proton gradient across the membrane. By a series of biochemical and biophysical approaches, several functionally important residues in the transmembrane region have been identified and our model of the SecDF function has been verified.

No MeSH data available.


Related in: MedlinePlus