A requirement for ankyrin binding to clathrin during coated pit budding. (17/741)

Recent studies suggest that the mobility of clathrin-coated pits at the cell surface are restricted by an actin cytoskeleton and that there is an obligate reduction in the amount of spectrin on membranes during coated pit budding. The spectrin-actin cytoskeleton associates with membranes primarily through ankyrins, which interact with the cytoplasmic region of numerous integral membrane proteins. We now report that the fourth repeat domain (D4) of ankyrin(R) binds to the N-terminal domain of clathrin heavy chain with high affinity. Addition of peptides containing the D4 region inhibited clathrin-coated pit budding in vitro. In addition, microinjection of D4 containing peptides blocked the endocytosis of fluorescent low density lipoprotein (LDL). Ankyrin(R) peptides that contained repeat domains other than D4 had no effect on either in vitro budding or internalization of LDL. Finally, immunofluorescence shows that ankyrin is uniformly associated with endosomes that contain fluorescent LDL. These results suggest that ankyrin plays a role in the budding of clathrin-coated pits during endocytosis.  (+info)

Crystal structure of the ARF-GAP domain and ankyrin repeats of PYK2-associated protein beta. (18/741)

ADP ribosylation factors (ARFs), which are members of the Ras superfamily of GTP-binding proteins, are critical components of vesicular trafficking pathways in eukaryotes. Like Ras, ARFs are active in their GTP-bound form, and their duration of activity is controlled by GTPase-activating proteins (GAPs), which assist ARFs in hydrolyzing GTP to GDP. PAPbeta, a protein that binds to and is phosphorylated by the non-receptor tyrosine kinase PYK2, contains several modular signaling domains including a pleckstrin homology domain, an SH3 domain, ankyrin repeats and an ARF-GAP domain. Sequences of ARF-GAP domains show no recognizable similarity to those of other GAPs, and contain a characteristic Cys-X(2)-Cys-X(16-17)-Cys-X(2)-Cys motif. The crystal structure of the PAPbeta ARF-GAP domain and the C-terminal ankyrin repeats has been determined at 2.1 A resolution. The ARF-GAP domain comprises a central three-stranded beta-sheet flanked by five alpha-helices, with a Zn(2+) ion coordinated by the four cysteines of the cysteine-rich motif. Four ankyrin repeats are also present, the first two of which form an extensive interface with the ARF-GAP domain. An invariant arginine and several nearby hydrophobic residues are solvent exposed and are predicted to be the site of interaction with ARFs. Site-directed mutagenesis of these residues confirms their importance in ARF-GAP activity.  (+info)

Axo-glial interactions regulate the localization of axonal paranodal proteins. (19/741)

Mice incapable of synthesizing the abundant galactolipids of myelin exhibit disrupted paranodal axo-glial interactions in the central and peripheral nervous systems. Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier. Whereas the clustering of the nodal proteins, sodium channels, ankyrin(G), and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered. The potassium channels, which are normally concentrated in the paranode/juxtaparanode, were not restricted to this region but were detected throughout the internode in the galactolipid-defi- cient mice. Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions. Collectively, these findings suggest that the myelin galactolipids are essential for the proper formation of axo-glial interactions and demonstrate that a disruption in these interactions results in profound abnormalities in the molecular organization of the paranodal axolemma.  (+info)

Improved sensitivity of PCR for diagnosis of human granulocytic ehrlichiosis using epank1 genes of Ehrlichia phagocytophila-group ehrlichiae. (20/741)

The agent of human granulocytic ehrlichiosis (HGE), Ehrlichia phagocytophila, and Ehrlichia equi probably comprise variants of a single Ehrlichia species now called the Ehrlichia phagocytophila genogroup. These variants share a unique 153-kDa protein antigen with ankyrin repeat motifs encoded by the epank1 gene. The epank1 gene was investigated as an improved target for PCR diagnosis of HGE compared with the currently used 16S rRNA gene target. Primers for epank1 flanking a region that spans part of the 5' ankyrin repeat coding region and part of the unique 3' region were synthesized. Blood samples from 31 patients with suspected HGE who were previously tested by 16S rRNA gene (16S) PCR and indirect immunofluorescent antibody test (IFA) were retrospectively tested with the epank1 primers. Eleven patients were 16S PCR positive and had a seroconversion detected by IFA (group A), 10 patients were 16S PCR negative but had a seroconversion detected by IFA (group B), and 10 patients were 16S PCR negative and seronegative (group C). Ten of the 11 group A patients were epank1 PCR positive, all 10 of the group B patients were epank1 PCR positive, and all of the PCR-negative and seronegative patients (group C) were epank1 PCR negative. The epank1 primers are more sensitive than the previously used 16S rRNA gene primers and therefore may be more useful in diagnostic testing for HGE.  (+info)

Association of L-arginine transporters with fodrin: implications for hypoxic inhibition of arginine uptake. (21/741)

In this study, we investigated the possible interaction between the cationic amino acid transporter (CAT)-1 arginine transporter and ankyrin or fodrin. Because ankyrin and fodrin are substrates for calpain and because hypoxia increases calpain expression and activity in pulmonary artery endothelial cells (PAEC), we also studied the effect of hypoxia on ankyrin, fodrin, and CAT-1 contents in PAEC. Exposure to long-term hypoxia (24 h) inhibited L-arginine uptake by PAEC, and this inhibition was prevented by calpain inhibitor 1. The effects of hypoxia and calpain inhibitor 1 were not associated with changes in CAT-1 transporter content in PAEC plasma membranes. However, hypoxia stimulated the hydrolysis of ankyrin and fodrin in PAEC, and this could be prevented by calpain inhibitor 1. Incubation of solubilized plasma membrane proteins with anti-fodrin antibodies resulted in a 70% depletion of CAT-1 immunoreactivity and in a 60% decrease in L-arginine transport activity in reconstituted proteoliposomes (3,291 +/- 117 vs. 8,101 +/- 481 pmol. mg protein(-1). 3 min(-1) in control). Incubation with anti-ankyrin antibodies had no effect on CAT-1 content or L-arginine transport in reconstituted proteoliposomes. These results demonstrate that CAT-1 arginine transporters in PAEC are associated with fodrin, but not with ankyrin, and that long-term hypoxia decreases L-arginine transport by a calpain-mediated mechanism that may involve fodrin proteolysis.  (+info)

Abnormal cardiac Na(+) channel properties and QT heart rate adaptation in neonatal ankyrin(B) knockout mice. (22/741)

The cytoskeleton of the cardiomyocyte has been shown to modulate ion channel function. Cytoskeletal disruption in vitro alters Na(+) channel kinetics, producing a late Na(+) current that can prolong repolarization. This study describes the properties of the cardiac Na(+) channel and cardiac repolarization in neonatal mice lacking ankyrin(B), a cytoskeletal "adaptor" protein. Using whole-cell voltage clamp techniques, I(Na) density was lower in ankyrin(B)(-/-) ventricular myocytes than in wild-type (WT) myocytes (-307+/-26 versus -444+/-39 pA/pF, P<0.01). Ankyrin(B)(-/-) myocytes exhibited a hyperpolarizing shift in activation and inactivation kinetics compared with WT. Slower recovery from inactivation contributed to the negative shift in steady-state inactivation in ankyrin(B)(-/-). Single Na(+) channel mean open time was longer in ankyrin(B)(-/-) versus WT at test potentials (V(t)) of -40 mV (1.0+/-0.1 versus 0. 61+/-0.04 ms, P<0.05) and -50 mV (0.8+/-0.1 versus 0.39+/-0.05 ms, P<0.05). Ankyrin(B)(-/-) exhibited late single-channel openings at V(t) -40 and -50 mV, which were not seen in WT. Late I(Na) contributed to longer action potential durations measured at 90% repolarization (APD(90)) at 1 Hz stimulation in ankyrin(B)(-/-) compared with WT (354+/-26 versus 274+/-22 ms, P<0.05). From ECG recordings of neonatal mice, heart rates were slower in ankyrin(B)(-/-) than in WT (380+/-14 versus 434+/-13 bpm, P<0.01). Although the QT interval was similar in ankyrin(B)(-/-) and WT at physiological heart rates, QT-interval prolongation in response to heart rate deceleration was greater in ankyrin(B)(-/-). In conclusion, Na(+) channels in ankyrin(B)(-/-) display reduced I(Na) density and abnormal kinetics at the whole-cell and single-channel level that contribute to prolonged APD(90) and abnormal QT-rate adaptation.  (+info)

I. Cellular and molecular biology of sodium channel beta-subunits: therapeutic implications for pain? I. Cellular and molecular biology of sodium channel beta-subunits: therapeutic implications for pain? (23/741)

Voltage-gated sodium channel alpha-subunits have been shown to be key mediators of the pathophysiology of pain. The present review considers the role of sodium channel auxiliary beta-subunits in channel modulation, channel protein expression levels, and interactions with extracellular matrix and cytoskeletal signaling molecules. Although beta-subunits have not yet been directly implicated in pain mechanisms, their intimate association with and ability to regulate alpha-subunits predicts that they may be a viable target for therapeutic intervention in the future. It is proposed that multifunctional sodium channel beta-subunits provide a critical link between extracellular and intracellular signaling molecules and thus have the ability to fine tune channel activity and electrical excitability.  (+info)

Sodium channel beta subunits mediate homophilic cell adhesion and recruit ankyrin to points of cell-cell contact. (24/741)

Sodium channels isolated from mammalian brain are composed of alpha, beta1, and beta2 subunits. The auxiliary beta subunits do not form the ion conducting pore, yet play important roles in channel modulation and plasma membrane expression. beta1 and beta2 are transmembrane proteins with one extracellular V-set immunoglobulin (Ig) protein domain. It has been shown recently that beta1 and beta2 interact with the extracellular matrix proteins tenascin-C and tenascin-R. In the present study we show that rat brain beta1 and beta2, but not alphaIIA, subunits interact in a trans-homophilic fashion, resulting in recruitment of the cytoskeletal protein ankyrin to sites of cell-cell contact in transfected Drosophila S2 cells. Whereas alphaIIA subunits expressed alone do not cause cellular aggregation, beta subunits co-expressed with alphaIIA retain the ability to adhere and recruit ankyrin. Truncated beta subunits lacking cytoplasmic domains interact homophilically to produce cell aggregation but do not recruit ankyrin. Thus, the cytoplasmic domains of beta1 and beta2 are required for cytoskeletal interactions. It is hypothesized that sodium channel beta subunits serve as a critical communication link between the extracellular and intracellular environments of the neuron and may play a role in sodium channel placement at nodes of Ranvier.  (+info)