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L Stryer

Publications and source records attributed to L Stryer.

At least 91 records · Page 5Linked to original sources
PubMed1982

Mechanism of interaction of Dictyostelium severin with actin filaments.

Severin, a 40,000-dalton protein from Dictyostelium that disassembles actin filaments in a Ca2+ -dependent manner, was purified 500-fold to greater than 99% homogeneity by modifications of the procedure reported by Brown, Yamamoto, and Spudich (1982. J. Cell Biol. 93:205-210). Severin has a Stokes radius of 29 A and consists of a single polypeptide chain. It contains a single methionyl and five cysteinyl residues. We studied the action of severin on actin filaments by electron microscopy, viscometry, sedimentation, nanosecond emission anisotropy, and fluorescence energy transfer spectroscopy. Nanosecond emission anisotropy of fluoresence-labeled severin shows that this protein changes its conformation on binding Ca2+. Actin filaments are rapidly fragmented on addition of severin and Ca2+, but severin does not interact with actin filaments in the absence of Ca2+. Fluorescence energy transfer measurements indicate that fragmentation of actin filaments by severin leads to a partial depolymerization (t1/2 approximately equal to 30 s). Depolymerization is followed by exchange of a limited number of subunits in the filament fragments with the disassembled actin pool (t1/2 approximately equal to 5 min). Disassembly and exchange are probably restricted to the ends of the filament fragments since only a few subunits in each fragment participate in the disassembly or exchange process. Steady state hydrolysis of ATP by actin in the presence of Ca2+-severin is maximal at an actin: severin molar ratio of approximately 10:1, which further supports the inference that subunit exchange is limited to the ends of actin filaments. The observation of sequential depolymerization and subunit exchange following the fragmentation of actin by severin suggests that severin may regulate site-specific disassembly and turnover of actin filament arrays in vivo.

Actins↗
PubMed1981

Retinal chromophore of rhodopsin photoisomerizes within picoseconds.

A new picosecond resonance Raman technique shows that resonance Raman lines characteristic of a distorted all-trans retinal appear within 30 picoseconds after photolysis of rhodopsin or isorhodopsin. This finding suggests that isomerization is nearly complete within picoseconds of the absorption of a photon.

Animals↗
PubMed1981

Flow of information in the light-triggered cyclic nucleotide cascade of vision.

Photolyzed rhodopsin catalyzes the exchange of GTP for FDP bound to a protein in retinal rod outer segments. We previously proposed that the GTP complex of this protein regulates the cyclic GMP phosphodiesterase and that it may be the first amplified intermediate in visual excitation [Fung, B. K.-K. & Stryer, L. (1980) Proc. Natl. Acad. Sci. USA 77, 2500-2504]. We report here the identification and characterization of transducin, a regulatory protein consisting of three kinds of polypeptide chains: T alpha (39 kilodaltons), T beta (36 kilodaltons), and T gamma (approximately 10 kilodaltons). Reconstituted membranes containing transducin and rhodopsin but no phosphodiesterase exhibit GTPase activity and amplified binding of guanosine 5'[beta, gamma-imido]triphosphate (p[NH]ppG), a nonhydrolyzable analog of GTP, on illumination. A single photolyzed rhodopsin molecule led to the uptake of p[NH]ppG by 71 molecules of transducin. High-pressure liquid chromatography showed that the binding site for GTP is on the alpha subunit of transducin. The isolation of the complex of ;[NH]ppG with T alpha enabled us to determine whether this species is the activator of the phosphodiesterase. We found that phosphodiesterase on unilluminated disc membranes can indeed be fully activated by addition of T alpha containing bound p[NH]ppG. These findings strongly suggest that transducin is the first amplified information-carrying intermediate in the cyclic nucleotide cascade of vision.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1981

Detection of actin assembly by fluorescence energy transfer.

Fluorescence energy transfer was used to measure the assembly and disassembly of actin filaments. Actin was labeled at cysteine 373 with an energy donor (5-iodoacetamidofluorescein) or an energy acceptor (tetramethylrhodamine iodoacetamide or eosin iodoacetamide). Donor-labeled actin and acceptor-labeled actin were coassembled. The dependence of the transfer efficiency on the mole fraction of acceptor-labeled actin showed that the radial coordinate of the label at cysteine 373 is approximately 35 A, which means that this site is located near the outer surface of the filament. The distance between a donor and the closest acceptor in such a filament is 58 A. The increase in fluorescence after the mixing of actin filaments containing both donor and acceptor with unlabeled filaments showed that there is a slow continuous exchange of actin units. The rate of exchange was markedly accelerated when the filaments were sonicated. The rapid loss of energy transfer caused by mechanical shear probably resulted from an increase in the number of filament ends, which in turn accelerated the exchange of monomeric actin units. Energy transfer promises to be a valuable tool in characterizing the assembly and dynamics of actin and other cytoskeletal and contractile proteins in vitro and in intact cells.

Actins↗
PubMed1981

Rapid motions in protein molecules.

Rapid motions of protein molecules can be detected by optical techniques that exploit short light pulses. Nanosecond fluorescence polarization studies have shown that whole domains of proteins such as immunoglobin G and myosin can rotate over an appreciable angular range of times of nanoseconds. This type of motion, called segmental flexibility, may be characteristic of many large proteins and molecular assemblies. Time-resolved fluorescence polarization studies have also demonstrated that internal tryptophan residues in some proteins, such as azurin, are quite flexible in the subnanosecond time range. Vary rapid conformational transitions of chromophoric groups can also be viewed by resonance Raman spectroscopy, which displays vibrations that are coupled to electronic transitions. In these experiments, intense light pulses are used to trigger a change in a photolabile molecule. The resonance Raman spectrum of rhodopsin photolysed by a 30 ps pulse from a Nd:YAG laser exhibits lines that are characteristic of a distorted all-trans retinal chromophore. This finding suggest that much of the cis-trans isomerization of retinal is accomplished within a few picoseconds of the absorption of a photon by rhodopsin. The emerging picture is that proteins can be designed by nature to allow very rapid motions of selected regions.

Fluorescence Polarization↗
PubMed1980

Photolyzed rhodopsin catalyzes the exchange of GTP for bound GDP in retinal rod outer segments.

We have studied the binding of guanyl nucleotides to retinal rod outer segment membranes to determine how light activates a cyclic GMP phosphodiesterase and a GTPase. We found that rod outer segment membranes contain tightly bound radioactive GDP after incubation in the dark with [3H]GDP or [alpha-32P]GTP. Reconstituted membranes containing only rhodopsin and phospholipid bind almost no GDP. More than 80% of the radioactive GDP bound to rod outer segment membranes could be released by subsequent illumination. At low light levels, the rate and extent of GDP release were markedly enhanced by the presence of GTP or p[NH]ppG, a nonhydrolyzable analog of GTP. The kinetics of binding of p[NH]ppG paralleled the kinetics of release of bound GDP, indicating that p[NH]ppG was exchanged for bound GDP. The maximal amount of bound p[NH]ppG was 1 per 30 rhodopsins when photolyzed membranes were incubated with 10 micro M nucleotide. Under these conditions, p[NH]ppG binding was half-maximal when only 1 in 90,000 rhodopsins was photolyzed. This corresponds to the catalyzed exchange of 500 p[NH]ppG for bound GDP per photolyzed rhodopsin. We propose a light-activated GTP-GDP amplification cycle involving a guanyl nucleotide binding protein with GTPase activity (E). The essence of this cycle is that photolyzed rhodopsin catalyzes the formation of E . GTP from E . GDP (the major species in the dark) by nucleotide exchange. The formation of several hundred E . GTP per photolyzed rhodopsin may be the first stage of amplification in visual excitation.

Animals↗
PubMed1979

Subnanosecond motions of tryptophan residues in proteins.

The dynamics of protein molecules in the subnanosecond and nanosecond time range were investigated by time-resolved fluorescence polarization spectroscopy. Synchrotron radiation from a storage ring was used as a pulsed light source to excite the single tryptophan residue in a series of proteins. The full width at half maximum of the detected light pulse was 0.65 nsec, making it feasible to measure emission anisotropy kinetics in the subnanosecond time range and thereby to resolve internal rotational motions. The proteins investigated exhibit different degrees of rotational freedom of their tryptophan residue, ranging from almost no mobility to nearly complete freedom in the subnanosecond time range. The tryptophan residue of Staphylococcus aureus nuclease B (20,000 daltons) has a single rotational correlation time (varphi) of 9.9 nsec at 20 degrees C, corresponding to a rotation of the whole protein molecule. By contrast, bovine basic A1 myelin protein (18,000 daltons) exhibits varphi of 0.09 and 1.26 nsec, showing that the tryptophan residue in this protein is highly flexible. The single tryptophan of human serum albumin (69,000 daltons) has almost no rotational freedom at 8 degrees C (varphi = 31.4 nsec), whereas at 43 degrees C it rotates rapidly (varphi(1) = 0.14 nsec) within a cone of semiangle 26 degrees in addition to rotating together with the whole protein (varphi(2) = 14 nsec). Of particular interest in the large angular range (semiangle, 34 degrees ) and fast rate (varphi(1) = 0.51 nsec) of the rotational motion of the tryptophan residue in Pseudomonas aeruginosa azurin (14,000 daltons). This residue is known to be located in the hydrophobic interior of the protein. The observed amplitudes and rates of these internal motions of tryptophan residues suggest that elementary steps in functionally significant conformational changes may take place in the subnanosecond time range.

Apoproteins↗
PubMed1978

Fluorescence energy transfer in the rapid-diffusion limit.

Energy transfer is enhanced by translational diffusion of the donor and acceptor [Steinberg, I. Z. & Katchalski, E. (1968) J. Chem. Phys. 48, 2404-2410]. The effect of diffusion on energy transfer depends on Dtau(0)/s(2), in which D is the sum of the diffusion coefficients of the donor and acceptor, tau(0) is the lifetime of the donor in the absence of transfer, and s is the mean distance between donors and acceptors. In most previous studies, Dtau(0)/s(2) << 1, corresponding to the static limit. We report here steady-state and kinetic fluorescence experiments showing that Dtau(0)/s(2) >> 1, the rapid-diffusion limit, can be attained by using Tb(3+) chelated to dipicolinate as a long-lived energy donor (tau(0) = 2.2 msec). The concentration of rhodamine B, the energy acceptor, resulting in 50% transfer was 0.67 muM, which is three orders of magnitude less than the concentration giving 50% transfer in the static limit. The dependence of the transfer efficiency on diffusion coefficients varying from 5 x 10(-11) to 1.5 x 10(-4) cm(2)/sec, spanning the range from the static limit to the rapid-diffusion limit, is in excellent agreement with theory. It is evident that energy donors with millisecond or longer excited state lifetimes can be used to probe translational motions in membranes and other assemblies. Energy transfer in the rapid diffusion limit is sensitive to the distance of closest approach (a) of the donor and acceptor. For a Tb.(DPA)(3) chelate trapped inside the aqueous space of a membrane vesicle containing eosin phosphatidylethanolamine, a = 10 A. The transverse location of chromophores in model membranes and biological membranes can be determined by this technique.

Journal Article↗