Specific interaction of the intermediate filament protein vimentin and its isolated N-terminus with negatively charged phospholipids as determined by vesicle aggregation, fusion, and leakage measurements

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Abstract
The interaction of the intermediate filament protein vimetin and its non-.alpha.-helical N-terminus with phosphatidylserine and phosphatidylinositol small unilamellar vesicles was investigated by measuring vesicle aggregation, fusion, and leakage. While the N-terminus suppressed Ca2+-induced fusion of phosphatidylserine vesicles, it caused their rapid aggregation in the absnece of Ca2+; at a molar ratio of lipid to polypeptide of 25:3, the polypeptide/lipid complexes precipitated from the reaction mixture. This aggregation was efficiently diminished by NaCl. The phosphatidylinositol vesicles, on the other hand, became leaky when interacting the N-terminus of vimetin, even at a molar ratio of lipid to polypeptide of 500:1. The leakage of phosphatidylinisitol vesicles was suppressed by the addition of Ca2+ or NaCl to the reaction mixture. Intact vimetin also caused leakage of phosphatidylinositol vesicles, at low and high salt concentration. The results indicate specific and differential interactions of the N-terminus of vimetin with various negatively charged lipid species, although there is an electrostatic component common to these interactions.

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