Model for the structure of bacteriorhodopsin based on high-resolution electron cryo-microscopy.

Publisher Summary The chapter discusses the stability of proteins and presents the results obtained on small compact globular proteins, which represent one single cooperative system. Protein is a cooperative system and behaves in an all-or-none fashion. Sharp changes in the properties of a protein do not mean anything in themselves because sequential multistep transitions exhibit the same sharp sigmoidal changes in the observed parameters. The problem of stability of native proteins is closely connected with the problem of protein denaturation, as stability can be judged only by breaking the native structure—that is, denaturing protein by various treatments. The pH of the solution is one of the most important factors determining the state of a protein. Potentiometric titration of protein revealed that smooth changes are connected with the titration of groups with a pK not very different from that of free amino acids, while the gross conformational changes associated with pH denaturation are accompanied by the unmasking of buried groups. The chapter also discusses the temperature-induced changes in protein, denaturational and predenaturational changes in protein, thermodynamics of protein unfolding, and thermodynamic properties of protein.

Stability of Proteins Small Globular Proteins

Fluidity Parameters of Lipid Regions Determined by Fluorescence Polarization

Steroid hormone receptors: Many Actors in search of a plot

The modification of mammalian membrane polyunsaturated fatty acid composition in relation to membrane fluidity and function

https://www.cell.com/biophysj/pdf/S0006-3495(77)85550-1.pdf

A theory of fluorescence polarization decay in membranes.

Molecular motions in liposomes of dipalmitoyl- phosphatidylcholine (DPPC) were studied by nanosecond fluorescence techniques. As a fluorescent probe for the hy- drocarbon region, 1,6-diphenyl-1,3,5-hexatriene (DPH) was used. Time courses of fluorescence intensity ZT(t) and emission anisotropy r(t) of DPH embedded in DPPC liposomes were measured at various temperatures. The value of the fluores- cence lifetime 7 obtained from a single exponential decay of Ir(t) was somewhat higher than that in liquid paraffin below the transition temperature TI and decreased above TI. Higher values of 7 below TI, indicate the almost complete hydrophobic environment. The decay curves of r(t) were separated into two phases: an initial fast decreasing phase of the order of one nanosecond and a second almost constant phase. This indicates Structure and dynamics of lipids in biological membranes have been recognized as the essential factors in their functions and organization (Inesi et al., 1973; Racker and Hinkle, 1974). Phospholipids in model membranes such as aqueous disper- sions or liposomes are known to be in a bilayer structure and the cooperative melting of their hydrocarbon chains, the crystalline-liquid-crystalline phase transition, takes place at a certain temperature (Trauble and Eibl, 1974; Sackmann et al., 1973; Chapman, 1975; Jacobson and Papahadjopoulos, 1975). Studies of dynamic properties or molecular motion of lipids in model bilayers, however, have not resolved several important questions. Although the use of spin-label techniques for the dynamic studies of lipid bilayers is widespread, the information re- garding molecular motion is restricted in most investigations. In describing the characteristics of molecular motion of that the orientational motion of DPH in the hydrocarbon re- gion is described by a wobbling diffusion restricted by a certain anisotropic potential. The results were analyzed on the model that the wobbling diffusion is confined in a cone with a uniform diffusion constant. Though temperature dependence of the cone angie was sigmoidal, that of the wobbling diffusion con- stant was like the exponential function. The change in the cone angle at TI was sharper than that in the wobbling diffusion constant at TI. Estimated values of the viscosity in the cone were an order of magnitude smaller than the values of "mi- croviscosity" which were estimated from the steady-state emission anisotropy without considering the restrictions on the rotational motion.

/pdf/dynamic-structure-of-lipid-bilayers-studied-by-nanosecond-3ewpbd7wyl.pdf

Dynamic Structure of Lipid Bilayers Studied by Nanosecond Fluorescence Techniques

http://www.k2.phys.waseda.ac.jp/PDF/1988BJ_KK_PulsedLM.pdf

Electroporation of cell membrane visualized under a pulsed-laser fluorescence microscope.

http://www.k2.phys.waseda.ac.jp/PDF/1982BJ_KK_Wobble.pdf

On the wobbling-in-cone analysis of fluorescence anisotropy decay

The motional properties of the hydrophobic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene have been assessed in liposomes of various lecithins: dipalmitoyl-phosphatidylcholine (DPPC), dioleoylphosphatidylcholine, 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), 1- palmitoyl-2-linoleoylphosphatidylcholine (PLPC), and 1-palmitoyl-2-arachidonoylphosphatidylcholine (PAPC). The temperature dependence of the steady-state fluorescence anisotropy was determined within the range of 10-50 degrees C. Nanosecond measurements were also made and the results analyzed by a model of wobbling diffusion confined within a cone. In this treatment the cone angle (theta c) obtained relates to the degree of order of the fatty acyl chains, and the wobbling diffusion constant (Dw) relates to the rate of motion of the hydrocarbon chains. Theta c was increased (order decreased) and Dw increased (rate increased) for the first double bond (POPC) as compared to the fully saturated DPPC. In all four unsaturated lecithins the temperature dependences of theta c and Dw were similar: theta c increased by about 4-5 degrees, and Dw increased by a factor of 1.5 per 10 degrees C. DPPC in the liquid-crystalline phase also showed a similar trend. The absolute values, on the other hand, showed some differences: for theta c, DOPC (78 degrees at 37 degrees C) greater than PAPC (75 degrees) greater than POPC (70 degrees) congruent to PLPC (69 degrees) greater than DPPC (20 degrees), and for Dw, PAPC (0.28 ns-1) greater than DOPC (0.22 ns-1) congruent to PLPC (0.24 ns-1) greater than POPC (0.21 ns-1) greater than DPPC (0.05 ns-1). The differences among the unsaturated lecithins are relatively small suggesting that the first double bond introduced into a lecithin plays the most important role at physiological temperatures. In 1:1 mixtures of the disaturated lecithin, DPPC, with the unsaturated lecithins, the temperature of the phase transition of the former was lowered and broadened, by approximately the same amount, irrespective of the differences in unsaturation.

Akira Ikegami

Papers

A theory of fluorescence polarization decay in membranes.

Dynamic Structure of Lipid Bilayers Studied by Nanosecond Fluorescence Techniques

Electroporation of cell membrane visualized under a pulsed-laser fluorescence microscope.

On the wobbling-in-cone analysis of fluorescence anisotropy decay

Effect of double bonds on the dynamic properties of the hydrocarbon region of lecithin bilayers.