Lateral diffusion of membrane proteins.
We measured the lateral mobility of integral membrane proteins reconstituted in giant unilamellar vesicles (GUVs), using fluorescence correlation spectroscopy. Receptor, channel, and transporter proteins with 1-36 transmembrane segments (lateral radii ranging from 0.5 to 4 nm) and a alpha-helical peptide (radius of 0.5 nm) were fluorescently labeled and incorporated into GUVs. At low protein-to-lipid ratios (i.e., 10-100 proteins per microm(2) of membrane surface), the diffusion coefficient D displayed a weak dependence on the hydrodynamic radius (R) of the proteins [D scaled with ln(1/R)], consistent with the Saffman-Delbruck model. At higher protein-to lipid ratios (up to 3000 microm(-2)), the lateral diffusion coefficient of the molecules decreased linearly with increasing the protein concentration in the membrane. The implications of our findings for protein mobility in biological membranes (protein crowding of approximately 25,000 microm(-2)) and use of diffusion measurements for protein geometry (size, oligomerization) determinations are discussed.
Ramadurai
Sivaramakrishnan
S
Department of Biochemistry, Groningen Biomolecular science and Biotechnology Institute & Zernike Institute of Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Holt
Andrea
A
Krasnikov
Victor
V
van den Bogaart
Geert
G
Killian
J Antoinette
JA
Poolman
Bert
B
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D004058:Diffusion; D005456:Fluorescent Dyes / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
D001426:Bacterial Proteins; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D008565:Membrane Proteins; D010455:Peptides