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J Biol Chem. 2009 Mar 20;284(12):7897-902. doi: 10.1074/jbc.M808305200. Epub 2009 Jan 12.

Structure, binding, and activity of Syd, a SecY-interacting protein.

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  • 1Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T1Z3, Canada.


The Syd protein has been implicated in the Sec-dependent transport of polypeptides across the bacterial inner membrane. Using Nanodiscs, we here provide direct evidence that Syd binds the SecY complex, and we demonstrate that interaction involves the two electropositive and cytosolic loops of the SecY subunit. We solve the crystal structure of Syd and together with cysteine cross-link analysis, we show that a conserved concave and electronegative groove constitutes the SecY-binding site. At the membrane, Syd decreases the activity of the translocon containing loosely associated SecY-SecE subunits, whereas in detergent solution Syd disrupts the SecYEG heterotrimeric associations. These results support the role of Syd in proofreading the SecY complex biogenesis and point to the electrostatic nature of the Sec channel interaction with its cytosolic partners.

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