Lateral diffusion of M-13 coat protein in mixtures of phosphatidylcholine and cholesterol

• Published in: Biochemistry (Easton) Vol. 19; no. 25; pp. 5907 - 5911
• Main Authors: Smith, Lloyd M, Rubenstein, John L. R, Parce, J. Wallace, McConnell, Harden M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09.12.1980
• Subjects: Cholesterol; Coliphages; Diffusion; Kinetics; Lipid Bilayers; Liposomes; Phosphatidylcholines; Spectrometry, Fluorescence; Viral Proteins
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00566a037

The translational diffusion of fluorescent-labeled M-13 phage coat protein (FITC-M-13), an integral membrane protein, has been measured in mixtures of phosphatidylcholines and cholesterol, using a pattern photobleaching technique. At temperatures below the chain-melting transition temperature of dimyristoylphosphatidylcholine (DMPC) (23.8 degrees C), the lateral diffusion coefficient of M-13 shows a marked increase when the cholesterol concentration is increased above 20 mol %. A similar marked increase in the lateral diffusion coefficient of a fluorescent phospholipid is also observed. At temperatures above the chain-melting transition temperature of DMPC, a minimum is observed in the lateral diffusion coefficient of FITC-M-13 for cholesterol concentrations in the vicinity of 25 mol %. This minimum in the diffusion coefficient of FITC-M-13 is also observed at 25 mol % cholesterol in egg phosphatidylcholine at 15 degrees C. No such minimum is observed for the lateral diffusion coefficient of the fluorescent lipid. The lateral diffusion coefficient of FITC-M-13 is large (greater than 10(-9) cm2/s) at all cholesterol concentrations for temperatures above the chain-melting transition temperature of the phosphatidylcholine. Several other proteins contain hydrophobic regions similar to that of the M-13 coat protein. We anticipate that a number of proteins of this type will show similar diffusional behavior, in particular exhibiting rapid diffusion throughout a wide range of lipid composition.