Proteins lateral mobility

Besides the bilayer type dynamic interfaces there also exist dynamic interfaces involving SAMs. The cooperative dynamic nature of SAMs on gold has been confirmed previously [107], On 2D surfaces the level of mobility in gold-thiol SAMs has been looked at and is considered quite slow ranging from 10 18 to 10 14 cm2 s 1 ( 1 nm/h) [109,108] when compared to phospholipid and membrane protein, lateral mobilities of around 10 8 cm2 s... 

Corbett, J. D. Cho, M. R. Golan, D. E. Deoxygenation affects fluorescence photobleaching recovery measurements of red cell membrane protein lateral mobility. Biophys. J. 1994,66,25-30. 

Gingell, D., Owens, N. (1992). How do cells sense and respond to adhesive contacts Diffusion-trapping of laterally mobile membrane proteins at maturating adhesions may initiate signals leading to local cytoskeletal assembly response and lamella formation. J. Cell Sci. 101, 255-266. 

The fluidity of lipid bilayers permits dynamic interactions among membrane proteins. For example, the interactions of a neurotransmitter or hormone with its receptor can dissociate a transducer protein, which in turn will diffuse to interact with other effector proteins (Ch. 19). A given effector protein, such as adenylyl cyclase, may respond differently to different receptors because of mediation by different transducers. These dynamic interactions require rapid protein diffusion within the plane of the membrane bilayer. Receptor occupation can initiate extensive redistribution of membrane proteins, as exemplified by the clustering of membrane antigens consequent to binding bivalent antibodies [8]. In contrast to these examples of lateral mobility, the surface distribution of integral membrane proteins can be fixed by interactions with other proteins. Membranes may also be partitioned into local spatial domains consisting of networks... 

R. D. Tilton, A. P. Gast, and C. R. Robertson, Surface diffusion of interacting proteins. Effect of concentration on the lateral mobility of adsorbed bovine serum albumin, Biophys. J. 58, 1321-1326 (1990). 

Specific proteins can be covalently attached via a carbohydrate bridge to membrane-bound PI (glycosylphosphatidylinositol, or GPI). This allows GPI-anchored proteins rapid lateral mobility on the surface of the plasma membrane. A deficiency in the synthesis of GPI in hematopoietic cells results in a hemolytic disease, paroxysmal nocturnal hemoglobinuria. 

Proteins and lipids have considerable lateral mobility within membranes. 

Some proteins of eukaryotic plasma membranes are connected to the cytoskeleton this connection inhibits their lateral mobility with the membrane. 

Gambin Y, Lopez-Esparza R, Reffay M, Sierecki E, Gov NS, Genest M, Hodges RS, Urbach W. Lateral mobility of proteins in liquid membranes revisited. Proc. Natl. Acad. Sci. U.S.A. 2006 103 2098-2102. 

In contrast, proteins vary markedly in their lateral mobility. Some proteins are nearly as mobile as lipids, whereas others are virtually immobile. For example, the photoreceptor protein rhodopsin (Section 32.3.1). a very mobile protein, has a diffusion coefficient of 0.4 pm s f The rapid movement of rhodopsin is essential for fast signaling. At the other extreme is fibronectin, a peripheral glycoprotein that interacts with the extracellular matrix. For fibronectin, D is less than 10-4 pm2 s f Fibronectin has a very low mobility because it is anchored to actin filaments on the inside of the plasma membrane through integrin, a transmembrane protein that links the extracellular matrix to the cytoskeleton. 

In contrast, proteins vary markedly in their lateral mobility. Some pro-teins are nearly as mobile as lipids whereas others are virtually immobile. For... 

Among the various membrane properties that might need to be optimized for a particular application of the tethered membrane architecture and/or of any incorporated proteins we discuss only two key performance parameters, i.e., (1) the ability of the tethering system to swell by the up-take of a sufficient amount of water into the interstitial space between the lipid bilayer and the solid support, and (2) the high lateral mobility of the individual lipid molecules in the two opposing leaflets of the bilayer membrane. 

Nevertheless, GPI anchors have been proposed to (1) allow proteins an increased lateral mobility (2) mediate the release or secretion of proteins (3) target proteins to... 

Without a transmembrane domain, the lateral movement of GPI-anchored proteins is not restricted by interactions with the cytoskeleton. Many GPI-anchored proteins are receptors or adhesion molecules and freedom of movement in the membrane may be advantageous for the interactions with their ligands. GPI anchors, then, may impart an increased lateral mobility to their linked proteins. 

As attractive as this hypothesis is, there is no strong evidence supporting increased lateral mobility due to a GPI anchor. Although GPI-anchored Thy-1, alkaline phosphatase, and DAF [104,121,122] all have lateral diffusion coefficients higher than the average calculated for transmembrane proteins [123], GPI-anchored proteins, trypanosomal VSG [52] and sperm adhesion protein PH-20 [124,125] have lateral diffusion coefficients lower than the average transmembrane protein. 

Direct comparison of the lateral mobility of chimeric proteins, where the GPI anchor is replaced with a transmembrane domain, demonstrates little change in their mobility [126,127]. Removal of asparagine-linked oligosaccharides has a greater effect on the lateral movement of the transmembrane protein H-2L[128] than removal of its cytoplasmic tail [129]. Moreover, the lateral mobility of the sperm protein PH-20 changes during development [124]. 

Consequently, GPI anchors may provide increased lateral movement to some proteins, but interactions with other portions of these membrane proteins may have greater effects on their lateral mobility [127]. 

Most Lipids and Many Proteins Are Laterally Mobile in Biomembranes... 

The lateral movements of specific plasma-membrane proteins and lipids can be quantified by a technique called fluo rescence recovery after photobleaching (FRAP). With this method, described In Figure 5-6, the rate at which membrane llpid or protein molecules move—the diffusion coefficient— can be determined, as well as the proportion of the molecules that are laterally mobile. 

Most lipids and many proteins are laterally mobile in biomembranes. 

H. L. Scott and S.-L. Chemg, Biochim. Biophys. Acta, 510, 209 (1978). Monte Carlo Studies of Phospholipid Lamellae. Effects of Proteins, Cholesterol, Bilayer Curvature and Lateral Mobility on Order Parameters. 

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