Biochemical studies of the excitable membrane of Paramecium tetraurelia VI. Endogenous protein substrates for in vitro and in vivo phosphorylation in cilia and ciliary membranes

Influence of extremely low frequency electromagnetic fields on the swimming behavior of ciliates

Different species of ciliates (Paramecium biaurelia, Loxodes striatus, Tetrahymena thermophila) have been taken as model systems to study the effects of extremely low-frequency electromagnetic fields (50 Hz, 0.5-2.0 mT) on the cellular level. A dose-dependent increase in the mean swimming velocity and a decrease in the linearity of cell tracks were observed in all wild-type cells. In contrast, field-exposure did not increase the number of directional turns of the Paramecium tetraurelia pawn mutant (d4-500r), which is characterized by defective Ca2+-channels. The described changes indicate a direct effect of low frequency electromagnetic fields on the transport mechanisms of the cell membrane for ions controlling the motile activity of cilia.

Aggregation, fusion and aqueous content release from liposomes induced by lysozyme derivatives: effect on the lytic activity

Chemically modified lysozymes, namely: N-succinyl lysozyme, glycine methyl ester of N-succinyl lysozyme and oxoindole lysozyme have been prepared. Aggregation, fusion and leakage of phospholipid vesicles induced by these derivatives have been studied in comparison with the effect of the unmodified protein. The experiments were carried out with negatively charges 9PC/PA, 9:1) and uncharged (PC and PC/DOPE/Chol (10:5:5)) lipid vesicles of different packing. Fusion and aggregation of negatively charged phospholipid vesicles in induced by proteins positively charged at pH 7.0 involving electrostatic interactions, a similar pattern on fusion and aggregation of the least stably packed lipid vesicles points also to hydrophobic forces playing a role in the lipid-protein interaction. A conformational change of the protein involved increasing beta-turns, loops and unordered structure at the expenses of beta-sheet without affecting alpha helix content. The conformational effect is necessary to provoke the effects studied, since one of the derivatives (N-succinyl lysozyme) neither changes conformation nor causes aggregation and fusion of vesicles. However, there is no relationship between lysozyme activity and fusion or aggregation of lipid vesicles that catalytic and fusogenci sites of, indicating lysozyme are topographically different.

Protein substrates for cGMP-dependent protein phosphorylation in cilia of wild type and atalanta mutants of Paramecium

In the ciliated protozoan Paramecium, swimming direction is regulated by voltage-gated Ca2+ channels in the ciliary membrane. In response to depolarizing stimuli, intraciliary Ca2+ rises, triggering reversal of the ciliary power stroke and backward swimming. One class of Ca(2+)-unresponsive behavioral mutants of Paramecium, atalanta mutants, cannot swim backward even though they have functional Ca2+ channels in their ciliary membrane. Several atalanta mutants were characterized with regard to several Ca(2+)-dependent activities, but no significant difference between wild type and the mutants was detected. However, one allelic group, atalanta A (initially characterized by Hinrichsen and Kung [1984: Genet. Res. Camb. 43:11-20]), showed a helical swimming path of opposite handedness from that of wild-type cells when detergent-permeabilized cells ("models") were reactivated with MgATP. When cGMP-dependent protein kinase purified from wild-type cells was added to atalanta A models, the handedness of the swimming path was reversed. Cyclic GMP stimulated in vitro phosphorylation of several proteins in isolated cilia, and the pattern of phosphoproteins was very similar for wild type and atalanta mutants, with one exception: a protein of 59 kDa was phosphorylated much less in the mutant ata A. When ciliary proteins were separated by gel electrophoresis and then phosphorylated "on blot" by purified cGMP-dependent protein kinase, phosphoprotein patterns were similar in wild type and ata mutants except that a 48 kDa protein (p48) from ata A3 was more heavily phosphorylated. This difference in p48 phosphorylation was also observed with cGMP-dependent protein kinase purified from ata A3 mutant cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The transmembrane signaling pathway involved in directed movements of Chlamydomonas flagellar membrane glycoproteins involves the dephosphorylation of a 60-kD phosphoprotein that binds to the major flagellar membrane glycoprotein

Cross-linking of Chlamydomonas reinhardtii flagellar membrane glycoproteins results in the directed movements of these glycoproteins within the plane of the flagellar membrane. Three carbohydrate-binding reagents (FMG-1 monoclonal antibody, FMG-3 monoclonal antibody, concanvalin A) that induce flagellar membrane glycoprotein crosslinking and redistribution also induce the specific dephosphorylation of a 60-kD (pI 4.8-5.0) flagellar phosphoprotein (pp60) that is phosphorylated in vivo on serine. Ethanol treatment of live cells induces a similar specific dephosphorylation of pp60. Affinity adsorption of flagellar 32P-labeled membrane-matrix extracts with the FMG-1 monoclonal antibody and concanavalin A demonstrates that pp60 binds to the 350-kD class of flagellar membrane glycoproteins recognized by the FMG-1 monoclonal antibody. In vitro, protein phosphatase 2B (calcineurin) removes 60% of the 32P from pp60; this correlates well with previous observations that directed flagellar glycoprotein movements are dependent on micromolar calcium in the medium and are inhibited by calcium channel blockers and calmodulin antagonists. The data reported here are consistent with the dephosphorylation of pp60 being a step in the signaling pathway that couples flagellar membrane glycoprotein cross-linking to the directed movements of flagellar membrane glycoproteins.

Identification of a family of casein kinases in Paramecium: biochemical characterization and cellular localization

Protein phosphorylation is believed to play a role in the regulation of ciliary motility in the protozoan Paramecium tetraurelia. Five protein kinases from Paramecium, activated by cyclic nucleotides or Ca2+, have been characterized previously. We report here the identification of a family of second-messenger-independent casein kinases in Paramecium. Casein kinase activity was enriched in the soluble fraction of cilia, but there was also significant activity tightly associated with axonemes. Three ciliary casein kinase activities (soluble CKS1 and CKS2, and axonemal CKA) were separated by chromatography and characterized. The native forms of all three were monomeric, with molecular masses of 28-45 kDa as judged by in-gel kinase assays and sizing by gel filtration. CKS2 was inhibited by heparin, but CKA was unaffected and CKS1 was stimulated. All three activities preferred acidic substrates such as casein and phosvitin, but they could be distinguished by their preference for other substrates. Antibodies against mammalian casein kinase I recognized CKS1 and CKS2 in immunoblots (43 kDa), but did not stain CKA. The antibodies to casein kinase I were used to probe other cellular fractions. A 65 kDa antigen (particulate casein kinase, CKP) was enriched in particulate fractions of whole cells. This 65 kDa protein was found in isolated cell cortices, but was not present in the infraciliary lattice. This report represents the first biochemical identification of a casein kinase I family in protozoa.

In vitro phosphorylation of ciliary dyneins by protein kinases from Paramecium

Paramecium dyneins were tested as substrates for phosphorylation by cAMP-dependent protein kinase, cGMP-dependent protein kinase, and two Ca(2+)-dependent protein kinases that were partially purified from Paramecium extracts. Only cAMP-dependent protein kinase caused significant phosphorylation. The major phosphorylated species was a 29 kDa protein that was present in both 22 S and 12 S dyneins; its phosphate-accepting activity peaked with 22 S dynein. In vitro phosphorylation was maximal at five minutes, then decreased. This decrease in phosphorylation was inhibited by the addition of vanadate or NaF. The 29 kDa protein was not phosphorylated by a heterologous cAMP-dependent protein kinase, the bovine catalytic subunit. Phosphorylation of dynein did not change its ATPase activity. In sucrose gradient fractions from the last step of dynein purification, phosphorylation by an endogenous kinase occurred. This phosphorylation could not be attributed to the small amounts of cAMP- and cGMP-dependent protein kinases known to be present, nor was it Ca(2+)-dependent. This previously uncharacterized ciliary protein kinase used casein as an in vitro substrate.

Identification of a 42 kDa protein as a substrate of protein phosphatase 1 in cilia from Paramecium

Okadaic acid, a specific inhibitor of protein phosphatase 1 in Paramecium causes sustained backward swimming in response to depolarising stimuli (S. Klumpp et al. (1990) EMBO J. 9, 685). Here, we employ okadaic acid, tautomycin, microcystin LR and inhibitor 1 as phosphatase inhibitors to identify a 42 kDa protein in the excitable ciliary membrane that is dephosphorylated by protein phosphatase 1. Identification of the 42 kDa protein was facilitated by the finding that the protein kinase responsible for its phosphorylation uses Ca-ATP as a substrate just as effectively as Mg-ATP. Notably, dephosphorylation of the 42 kDa protein is specifically inhibited by cyclic AMP; cyclic GMP has no effect.

Cyclic AMP-dependent protein kinases of Paramecium. I. Chromatographic and physical properties of the enzymes from cilia

The cAMP-dependent protein kinases of the cilia of the protozoan Paramecium tetraurelia were resolved and characterized. Two cAMP-dependent activities were present in cilia; the two ciliary kinases resemble types I and II from vertebrate tissues. Part of the ciliary kinase activity (primarily type II) was released by freeze-thawing, but a significant amount remained particulate. Both kinases were found as aggregates of about 220 kDa and of about 70 kDa. A portion of the cAMP-binding activity in ciliary extracts separated from kinase activity, and eluted at 36 kDa during gel filtration. Photoaffinity labeling with 8-azido-cAMP identified cAMP-binding proteins of 45-52 kDa in type II kinase from cilia, and of 43-46 kDa in type I kinase. The type II kinase was apparently autophosphorylated, causing a decrease in mobility during sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

In vitro phosphorylation of Paramecium axonemes and permeabilized cells

This study seeks to identify phosphoproteins in axonemes from Paramecium tetraurelia whose phosphorylation responses to adenosine 3', 5'-cyclic monophosphate (cAMP) and Ca2+ parallel responses induced by these agents in ciliary behavior in this cell. In purified axonemes, over 15 bands ranging from Mr greater than 300 kDa to 19 kDa on SDS-PAGE incorporate 32P from adenosine 5'-gamma-[32P]triphosphate (gamma-32P-ATP) at pCa 7 in the absence of cAMP. A major band whose label turns over rapidly was identified at Mr 43 kDa. In the presence of 5 microM cAMP, more than eight bands, but not the Mr 43 kDa band, were labeled additionally or enhanced their labeling. These phosphoproteins and their kinases are structural components of the axoneme. Overall, some of the same major bands are labeled in the presence of cAMP in Triton X-100-permeabilized paramecia that retain their behavioral responses and in axonemes mechanically isolated from these cells. In particular, two major bands have been identified whose phosphorylation is greatly enhanced by cAMP at low concentrations: 1) a 29 kDa polypeptide whose cAMP-dependent phosphorylation is diminished at pCa 4 compared with pCa 7 and 2) a 65 kDa polypeptide whose phosphorylation is pCa insensitive. These polypeptides meet minimal criteria for signal-sensitive regulators of motility parameters in the Paramecium axoneme.

Regulation of axonemal Mg2+-ATPase from Paramecium cilia: effects of Ca2+ and cyclic nucleotides

Ciliary activity is regulated by Ca2+ and cyclic nucleotides, but the molecular mechanisms of the regulation are unknown. We have tested the ability of Ca2+ and cyclic nucleotides to alter ciliary Mg2+-ATPase or to stimulate phosphorylation of axonemal dynein. Mg2+-ATPase activity in cilia and axonemes from Paramecium was stimulated 2-fold by micromolar Ca2+, but this Ca2+ sensitivity was lost upon solubilization of the dyneins from the axoneme. The Ca2+-sensitive component of ciliary Mg2+-ATPase activity was inhibited by the dynein inhibitors vanadate and Zn2+, but was insensitive to the calmodulin antagonists calmidazolium and melittin. Dynein activity in the high-salt extract from axonemes was also insensitive to calmidazolium. Calmodulin did not sediment with 22 S or 12 S dyneins on sucrose gradients containing Ca2+, but it did sediment in the region from 19 S to 14 S. Mg2+-ATPase activity in ciliary fractions was unaltered in the presence of cAMP or cGMP. However, polypeptides associated with the 22 S and 12 S dyneins, as well as proteins of 19 S, 15 S, and 8 S, were substrates for endogenous ciliary kinases. High molecular weight polypeptides that sedimented at 22 S and 19 S were phosphorylated in a cyclic nucleotide-stimulated manner.

Differential regulation of Paramecium ciliary motility by cAMP and cGMP

cAMP and cGMP had distinct effects on the regulation of ciliary motility in Paramecium. Using detergent-permeabilized cells reactivated to swim with MgATP, we observed effects of cyclic nucleotides and interactions with Ca2+ on the swimming speed and direction of reactivated cells. Both cAMP and cGMP increased forward swimming speed two- to threefold with similar half-maximal concentrations near 0.5 microM. The two cyclic nucleotides, however, had different effects in antagonism with the Ca2+ response of backward swimming and on the handedness of the helical swimming paths of reactivated cells. These results suggest that cAMP and cGMP differentially regulate the direction of the ciliary power stroke.

Identification, characterization, and functional correlation of calmodulin-dependent protein phosphatase in sperm

Preliminary data demonstrated that the inhibition of reactivated sperm motility by calcium was correlated with inhibited protein phosphorylation. The inhibition of phosphorylation by Ca2+ was found to be catalyzed by the calmodulin-dependent protein phosphatase (calcineurin). Sperm from dog, pig, and sea urchin contain both the Ca2+-binding B subunit of the enzyme (Mr 15,000) and the calmodulin-binding A subunit with an Mr of 63,000. The sperm A subunit is slightly higher in Mr than reported for other tissues. Inhibition of endogenous calmodulin-dependent protein phosphatase activity with a monospecific antibody revealed the presence of 14 phosphoprotein substrates in sperm for this enzyme. The enzyme was localized to both the flagellum and the postacrosomal region of the sperm head. The flagellar phosphatase activity was quantitatively extracted with 0.6 M KCl from isolated flagella from dog, pig, and sea urchin sperm. All salt-extractable phosphatase activity was inhibited with antibodies against the authentic enzyme. Preincubation of sperm models with the purified phosphatase stimulated curvolinear velocity and lateral head amplitude (important components of hyperactivated swimming patterns) and inhibited beat cross frequency suggesting a role for this enzyme in axonemal function. Our results suggest that calmodulin-dependent protein phosphatase plays a major role in the calcium-dependent regulation of flagellar motility.

Cyclic AMP-dependent protein phosphorylation in chemosensory neurons: identification of cyclic nucleotide-regulated phosphoproteins in olfactory cilia

Chemosensory dendritic membranes (olfactory cilia) contain protein kinase activity that is stimulated by cyclic AMP and more efficiently by the nonhydrolyzable GTP analog guanosine-5'-O-(3-thio)triphosphate (GTP gamma S). In control nonsensory (respiratory) cilia, the cyclic AMP-dependent protein kinase is practically GTP gamma S-insensitive. GTP gamma S activation of the olfactory enzyme appears to be mediated by a stimulatory GTP-binding protein (G-protein) and adenylate cyclase previously shown to be enriched in the sensory membranes. Protein kinase C activity cannot be detected in the chemosensory cilia preparation under the conditions tested. Incubation of olfactory cilia with [gamma-32P]ATP leads to the incorporation of [32P]phosphate into many polypeptides, four of which undergo covalent modification in a cyclic nucleotide-dependent manner. The phosphorylation of one polypeptide, pp24, is strongly and specifically enhanced by cyclic AMP at concentrations lower than 1 microM. This phosphoprotein is not present in respiratory cilia, but is seen also in membranes prepared from olfactory neuroepithelium after cilia removal. Cyclic AMP-dependent protein kinase and phosphoprotein pp24 may be candidate components of the molecular machinery that transduces odor signals.

Regulation of ciliary motility by membrane potential in Paramecium: a role for cyclic AMP

The membrane potential of Paramecium controls the frequency and direction of the ciliary beat, thus determining the cell's swimming behavior. Stimuli that hyperpolarize the membrane potential increase the ciliary beat frequency and therefore increase forward swimming speed. We have observed that 1) drugs that elevate intracellular cyclic AMP increased swimming speed 2-3-fold, 2) hyperpolarizing the membrane potential by manipulation of extracellular cations (e.g., K+) induced both a transient increase in, and a higher sustained level of cyclic AMP compared to the control, and 3) the swimming speed of detergent-permeabilized cells in MgATP was stimulated 2-fold by the addition of cyclic AMP. Our results suggest that the membrane potential can regulate intracellular cAMP in Paramecium and that control of swimming speed by membrane potential may in part be mediated by cAMP.

Ionic regulation of cyclic AMP levels in Paramecium tetraurelia in vivo

cAMP levels in Paramecium increased dose dependently after a step increase of [Ca] or [Sr] in the incubation, provided K was present. Two mM Ca or Sr tripled cAMP concentrations within 3 s and induced an increase in forward swimming speed. The increase in cAMP formation was strictly dependent on the Donnan ratio [K]: square root [Ca]. Na, Li, or tetraethylammonium could not replace K. The data provide evidence for regulation of cAMP in Paramecium by the membrane surface charge as determined specifically by the regulation of cAMP in Paramecium by the membrane surface charge as determined specifically by the K: Ca ratio.