Elicitins trap and transfer sterols from micelles, liposomes and plant plasma membranes

Using elicitins, proteins secreted by some phytopathogenic Oomycetes (Phyto phthora) known to be able to transfer sterols between phospholipid vesicles , the transfer of sterols between micelles, liposomes and biological membra nes was studied. Firstly, a simple fluorometric method to screen the sterol -carrier capacity of proteins, avoiding the preparation of sterol-containin g phospholipidic vesicles, is proposed. The transfer of sterols between DHE micelles (donor) and stigmasterol or cholesterol micelles (acceptor) was d irectly measured, as the increase in DHE fluorescence signal. The results o btained with this rapid and easy method lead to the same conclusions as tho se previously reported, using fluorescence polarization of a mixture of don or and acceptor phospholipid vesicles, prepared in the presence of differen t sterols. Therefore, the micelles method can be useful to screen proteins for their sterol carrier activity. Secondly, elicitins are shown to trap st erols from purified plant plasma membranes and to transfer sterols from mic elles to these biological membranes. This property should contribute to und erstand the molecular mechanism involved in sterol uptake by Phytophthora. It opens new perspectives concerning the role of such proteins in plant-mic roorganism interactions. (C) 1999 Elsevier Science B.V. All rights reserved .