Abstract
Targeting of many polytopic proteins to the inner membrane of prokaryotes occurs via an essential signal recognition particle-like pathway. FtsY, the Escherichia coli homolog of the eukaryotic signal recognition particle receptor alpha-subunit, binds to membranes via its amino-terminal AN domain. We demonstrate that FtsY assembles on membranes via interactions with phosphatidylethanolamine and with a trypsin-sensitive component. Both interactions are mediated by the AN domain of FtsY. In the absence of phosphatidylethanolamine, the trypsin-sensitive component is sufficient for binding and function of FtsY in the targeting of membrane proteins. We propose a two-step mechanism for the assembly of FtsY on the membrane similar to that of SecA on the E. coli inner membrane.
Highlights
From the ‡Department of Biochemistry, McMaster University, Hamilton, Ontario L8N 3Z5, Canada and the §Genetics and Biochemistry Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-1810
In Escherichia coli, most integral membrane proteins are targeted to the inner membrane via the signal recognition particle (SRP)1 [1,2,3,4], a particle composed of Ffh and 4.5 S RNA [5, 6]
To further investigate membrane binding of FtsY, we compared binding of full-length FtsY, FtsYAN, and, as a negative control, FtsYA synthesized in reticulocyte lysate to inverted vesicles (INVs) and canine microsomes (Fig. 1)
Summary
Vol 276, No 28, Issue of July 13, pp. 25982–25989, 2001 Printed in U.S.A. FtsY Binds to the Escherichia coli Inner Membrane via Interactions with Phosphatidylethanolamine and Membrane Proteins*. In the absence of PE, SRP-dependent protein targeting remains functional, and the FtsY membrane assembly domain binds to E. coli inner membrane inverted vesicles (INVs) via an interaction with a trypsin-sensitive component. This suggests that, similar to SecA of the general secretory pathway [23, 24], membrane assembly of FtsY involves interactions with both a specific lipid and a membrane protein. Based on these results and previously published data, we propose that FtsY binding to the membrane occurs initially through phospholipid binding, followed by targeting to translocation sites via an interaction with a membrane protein
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