Interaction in vitro of nonepithelial intermediate filament proteins with total cellular lipids, individual phospholipids, and a phospholipid mixture.

The interaction of nonepithelial intermediate filament (IF) proteins with vesicles produced from total Ehrlich ascites tumor cell lipids results in the formation of complexes which in sucrose density gradient centrifugation attain positions distinctly different from those of the original reactants. In KBr density gradient equilibrium centrifugation, the IF protein-lipid adducts accumulate as thin proteolipid films on top of the KBr gradients, whereas in the absence of lipids the proteins remain distributed within the density gradients. Similar results were obtained with vesicles derived from individual phospholipids and a mixture thereof. The affinity of IF proteins for negatively charged phospholipids is greater than that for vesicles derived from uncharged phospholipids. Limited digestion of IF proteins with various proteinases demonstrated that for optimal association of the reactants IF proteins must carry an intact N terminus and that the isolated N-terminal polypeptide itself shows strong reactivity with lipid vesicles. Arginine-phosphate interactions between the N terminus and phospholipids seem to be partly responsible for this association. However, as shown by hydrophobic interaction chromatography on phenyl- and octyl-Sepharose 4B, IF proteins and their proteolytic derivatives also appear to have high affinities for aromatic and aliphatic substructures of biologically important molecules. The results are discussed in terms of a possible functional role of IF protein-lipid interactions in the association of nonepithelial intermediate filaments with intracellular membrane systems.