Issue 7, 2005
From the journal:

Organic & Biomolecular Chemistry

New fluorescent probes reveal that flippase-mediated flip-flop of phosphatidylinositol across the endoplasmic reticulum membrane does not depend on the stereochemistry of the lipid†

Ram A. Vishwakarma,*a   Stefanie Vehring,b   Anuradha Mehta,a   Archana Sinha,a   Thomas Pomorski,b   Andreas Herrmannb  and  Anant K. Menon*c  

* Corresponding authors

a Bio-Organic Chemistry Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India
E-mail: ram@nii.res.in
Fax: +91-11-26162125
Tel: +91-11-26717121

b Institut für Biologie/Biophysik, Humboldt Universität zu Berlin, Invalidenstrasse 42, Berlin, Germany

c Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, USA
E-mail: menon@biochem.wisc.edu
Fax: +1-608-262-3453
Tel: +1-608-262-2913

Abstract

Glycerophospholipid flip-flop across biogenic membranes such as the endoplasmic reticulum (ER) is a fundamental feature of membrane biogenesis. Flip-flop requires the activity of specific membrane proteins called flippases. These proteins have yet to be identified in biogenic membranes and the molecular basis of their action is unknown. It is generally believed that flippase-facilitated glycerophospholipid flip-flop across the ER is governed by the stereochemistry of the glycerolipid, but this important issue has not been resolved. Here we investigate whether the ER flippase stereochemically recognizes the glycerophospholipids that it transports. To address this question we selected phosphatidylinositol (PI), a biologically important molecule with chiral centres in both its myo-inositol headgroup and its glycerol–lipid tail. The flip-flop of PI across the ER has not been previously reported. We synthesized fluorescence-labeled forms of all four diastereoisomers of PI and evaluated their flipping in rat liver ER vesicles, as well as in flippase-containing proteoliposomes reconstituted from a detergent extract of ER. Our results show that the flippase is able to translocate all four PI isomers and that both glycerol isomers of PI flip-flop across the ER membrane at rates similar to that measured for fluorescence-labeled phosphatidylcholine. Our data have important implications for recent hypotheses concerning the evolution of distinct homochiral glycerophospholipid membranes during the speciation of archaea and bacteria/eukarya from a common cellular ancestor.

Graphical abstract: New fluorescent probes reveal that flippase-mediated flip-flop of phosphatidylinositol across the endoplasmic reticulum membrane does not depend on the stereochemistry of the lipid

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Article information

DOI
https://doi.org/10.1039/B500300H
Article type
Paper
Submitted
10 Jan 2005
Accepted
14 Feb 2005
First published
01 Mar 2005

Org. Biomol. Chem., 2005,3, 1275-1283

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New fluorescent probes reveal that flippase-mediated flip-flop of phosphatidylinositol across the endoplasmic reticulum membrane does not depend on the stereochemistry of the lipid

R. A. Vishwakarma, S. Vehring, A. Mehta, A. Sinha, T. Pomorski, A. Herrmann and A. K. Menon, Org. Biomol. Chem., 2005, 3, 1275 DOI: 10.1039/B500300H

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