An isoform of the phosphatidylinositol-transfer protein transfers sphingomyelin and is associated with the Golgi system

Author:

de Vries K J1,Heinrichs A A J1,Cunningham E2,Brunink F1,Westerman J1,Somerharju P J3,Cockcroft S2,Wirtz K W A1,Snoek G T1

Affiliation:

1. Centre for Biomembranes and Lipid Enzymology, Utrecht University, Utrecht, The Netherlands

2. Deparment of Physiology, University College London, London, U.K.

3. Department of Basic Chemistry, University of Helsinki, Helsinki, Finland

Abstract

An isoform of the phosphatidylinositol-transfer protein (PI-TP) was identified in the cytosol fraction of bovine brain. This protein, designated PI-TP beta, has an apparent molecular mass of 36 kDa and an isoelectric point of 5.4. The N-terminal amino acid sequence (21 residues) is 90% similar to that of bovine brain PI-TP, henceforth designated PI-TP alpha (molecular mass 35 kDa and pI 5.5). As observed for PI-TP alpha, PI-TP beta has a distinct preference for phosphatidylinositol over phosphatidylcholine. In addition, it expresses a high transfer activity towards sphingomyelin. PI-TP alpha lacks this activity completely. By indirect immunofluorescence we demonstrated that, in Swiss mouse 3T3 fibroblasts, PI-TP beta is preferentially associated with the Golgi system whereas PI-TP alpha is predominantly present in the cytoplasm and the nucleus. In cytosol-depleted HL60 cells, both PI-TP alpha and PI-TP beta were equally effective at reconstituting guanosine 5′-[gamma-thio]triphosphate-mediated phospholipase C beta activity.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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