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At least 829 records · Page 46Linked to original sources
PubMed2003

A region of the C-terminal tail of the gp41 envelope glycoprotein of human immunodeficiency virus type 1 contains a neutralizing epitope: evidence for its exposure on the surface of the virion.

The approximately 150 amino acid C-terminal tail of the gp41 transmembrane glycoprotein of human immunodeficiency virus type 1 (HIV-1) is generally thought to be located inside the virion. However, we show here that both monoclonal IgG and polyclonal epitope-purified IgG specific for the (746)ERDRD(750) epitope that lies within the C-terminal tail neutralized infectious virus. IgG was mapped to the C-terminal tail by its failure to neutralize tail-deleted virus, and by sequencing of antibody-escape mutants. The fact that antibody does not cross lipid membranes, and infectious virus is by definition intact, suggested that ERDRD was exposed on the surface of the virion. This was confirmed by reacting virus and IgG, separating virus and unbound IgG by centrifugation, and showing that virus was neutralized to essentially the same extent as virus that had been in constant contact with antibody. Epitope exposure on virions was independent of temperature and therefore constitutive. Monoclonal antibodies specific to epitopes PDRPEG and IEEE, upstream of ERDRD, also bound to virions, suggesting that they too were located externally. Protease digestion destroyed the ERDRD and PDRPEG epitopes, consistent with their proposed external location. Altogether these data are consistent with part of the C-terminal tail of gp41 being exposed on the outside of the virion. Possible models of the structure of the gp41 tail, taking these observations into account, are discussed.

Amino Acid Sequence↗
PubMedDate not supplied

Direct comparison of serotonin effects on siphon versus tail sensory neurons in Aplysia.

Modulation of the strength of siphon and tail withdrawal reflexes in Aplysia involves, in part, changes in the sensory neurons that initiate these reflexes. Different observations and experiments on modulation in siphon and tail sensory neurons together contribute to the working model of mechanisms of learning and memory in Aplysia, yet no direct comparison of modulation in these two classes of sensory neurons has yet been made. The purpose of the present study was to directly compare modulation between siphon and tail sensory neurons in the same experimental conditions. In particular, we focused on the effects of serotonin on two firing properties of sensory neurons: spike duration and excitability. We applied serotonin (5-HT) onto both siphon and tail sensory neurons under the same conditions and found that both spike duration and excitability were significantly enhanced. This enhancement was statistically indistinguishable between siphon and tail sensory neurons tested simultaneously in the same preparation. Thus, these two different classes of sensory neurons respond to 5-HT in very similar, if not identical, ways. We conclude that if there are differences in 5-HT induced modulation between siphon and tail sensory neurons at the biophysical level, such differences are not strongly manifested at the level of changes in firing properties.

Animals↗
PubMed2006

Tail-induced attraction between nucleosome core particles.

We study a possible electrostatic mechanism underlying the compaction of DNA inside the nuclei of eucaryotes: the tail-bridging effect between nucleosomes, the fundamental DNA packaging units of the chromatin complex. As a simple model of the nucleosome we introduce the eight-tail colloid, a charged sphere with eight oppositely charged, flexible, grafted chains that represent the terminal histone tails. We show that our complexes attract each other via the formation of chain bridges and contrast this to the effect of attraction via charge patches. We demonstrate that the attraction between eight-tail colloids can be tuned by changing the fraction of charged monomers on the tails. This suggests a physical mechanism of chromatin compaction where the degree of DNA condensation is controlled via biochemical means, namely the acetylation and deacetylation of lysines in the histone tails.

Animals↗
PubMed2005

Integrin CD11a cytoplasmic tail interacts with the CD45 membrane-proximal protein tyrosine phosphatase domain 1.

Leucocyte adhesion receptor integrin CD11aCD18 and the transmembrane receptor-like protein tyrosine phosphatase (RPTP) CD45 mediate immune synapse formation and signalling during antigen presentation. Previous cocapping studies on human naïve T cells demonstrate an interaction between CD11aCD18 and CD45. CD45 cross-linking also has an effect on the ligand-binding activity of CD11aCD18. However, the mode of interaction between CD11aCD18 and CD45 remains unclear. Herein, yeast two-hybrid analysis identified a partial CD45 cytoplasmic tail interacting with that of CD11a. The CD45 cytoplasmic tail comprises a membrane proximal (Mp) region, protein tyrosine phosphatase domain 1 (D1), spacer, D2, and carboxyl terminus. CD45 Mp-D1 was found to be the main interacting region for the CD11a cytoplasmic tail. In contrast, the full-length CD45 cytoplasmic tail interacted weakly with that of CD11a. It has been reported that CD45 Mp-D1 but not the full-length cytoplasmic tail forms a homodimer whose enzymatic activity is inhibited. Our in vitro binding and enzymatic assays showed that the homodimeric CD45 cytoplasmic tail interacts with that of CD11a. The biological function of CD45 dimerization and its association with CD11a remains to be investigated.

Amino Acid Sequence↗
PubMed1993

A neurofilament-associated kinase phosphorylates only a subset of sites in the tail of chicken midsize neurofilament protein.

Although neurofilaments are among the most highly phosphorylated proteins extant, relatively little is known about the kinases involved in their phosphorylation. The majority of the phosphates present on the two higher-molecular-mass neurofilament subunits are added to multiply repeated sequence motifs in the tail. We have examined the specificity of a neurofilament-associated kinase (NFAK) partially purified from chicken spinal cord that selectively phosphorylates the middle-molecular-mass neurofilament subunit, NF-M. Two-dimensional phosphopeptide mapping of 32P-labeled NF-M shows that, in vitro, NFAK phosphorylates a subset of peptides phosphorylated in vivo in cultured neurons. The absence of a complete complement of labeled phosphopeptides following in vitro phosphorylation, compared with phosphorylation in vivo, is not due to a lack of availability of phosphorylation sites because the same maps are obtained when enzymatically dephosphorylated NF-M is used as an in vitro substrate. Phosphopeptide maps from in vitro-phosphorylated NF-M and those from a recombinant fusion protein containing only a segment of the tail piece of chicken NF-M reveal identical labeled peptides. The fusion protein lacks a segment containing 17 KXX(S/T)P putative phosphorylation sites contained in the tail of chicken NF-M but contains a segment that includes four KSPs and a KSD site also present in the intact tail. These results suggest (a) that NFAK mediates the phosphorylation of some, but not all, potential phosphorylation sites within the tail of NF-M and (b) that multiple kinases are necessary for complete phosphorylation of the NF-M tail.

Amino Acid Sequence↗
PubMed2000

Medial efferent effects on auditory-nerve responses to tail-frequency tones II: alteration of phase.

It is often assumed that at frequencies in the tuning-curve tail there is a passive, constant coupling of basilar-membrane motion to inner hair cell (IHC) stereocilia. This paper shows changes in the phase of auditory-nerve-fiber (ANF) responses to tail-frequency tones and calls into question whether basilar-membrane-to-IHC coupling is constant. In cat ANFs with characteristic frequencies > or = 10 kHz, efferent effects on the phase of ANF responses to tail-frequency tones were measured. Efferent stimulation caused substantial changes in ANF phase (deltaphi) (range -80 degrees to +60 degrees, average -15 degrees, a phase lag) with the largest changes at sound levels near threshold and 3-4 octaves below characteristic frequency (CF). At these tail frequencies, efferent stimulation had much less effect on the phase of the cochlear microphonic (CM) than on ANF phase. Thus, since CM is synchronous with basilar-membrane motion for low-frequency stimuli in the cochlear base, the efferent-induced change in ANF phase is unlikely to be due entirely to a change in basilar-membrane phase. At tail frequencies, ANF phase changed with sound level (often by 90 degrees-180 degrees) and the deltaphi from a fiber was positively correlated with the slope of its phase-versus-sound-level function at the same frequency, as if deltaphi were caused by a 2-4 dB increase in sound level. This correlation suggests that the processes that produce the change in ANF phase with sound level at tail frequencies are also involved in producing deltaphi. It is hypothesized that both efferent stimulation and increases in sound level produce similar phase changes because they both produce a similar mix of cochlear vibrational modes.

Animals↗
PubMed2004

The type 1 angiotensin II receptor tail affects receptor targeting, internalization, and membrane fusion properties.

Endocytosis modulates cell responses by removing and recycling receptors from the cell surface. Type I angiotensin II receptors (AT1R) are somewhat unique in that they are expressed at apical (AP) and basolateral (BL) membranes in proximal tubule cells and both receptor sites undergo endocytosis. We analyzed AT1R cytoplasmic (-COOH) tail deletion mutants to determine whether classic AT1R endocytosis motifs functioned similarly in polarized cells and simultaneously altered receptor properties. Serially truncating the AT1R tail had little effect on AP/BL AT1R distribution as determined by 125I-angiotensin II binding in LLCPK(Cl4) cells transfected with an AT1R transcript. AP AT1R expression required the proximal 12 amino acids in the AT1R-COOH tail. Deleting all but the proximal 12 aa of the AT1R-COOH tail (T316L mutant) decreased AP AT1R internalization at 20 min (17 +/- 6%; p < 0.05 versus full-length; n = 5) and inhibited AP AT1R-stimulated arachidonic acid release (counts released per milligram of protein at 20 min: full-length, 18,762 +/- 4018; T316L, 2430 +/- 1711; n = 4; p < 0.02). Endosomal fusion assays were performed using peptide sequences of regions in the AT1R tail involved in endocytosis (YFLQLLKYIPP [LL] and LSTKMSTLSY [STL]). Peptide STL significantly inhibited endosomal fusion (22 +/- 10% of control; n = 5; p < 0.05 versus positive control). Peptide LL had no significant inhibitory effect. AT(1)R in polarized cells contain dominant endocytosis signals but these motifs do not correlate with AP or BL AT1R expression. Moreover, peptide sequences within the AT1R-COOH tail necessary for endocytosis also modulate endosomal fusion properties.

Amino Acid Sequence↗
PubMed2006

Anatomy of a lactococcal phage tail.

Bacteriophages of the Siphoviridae family utilize a long noncontractile tail to recognize, adsorb to, and inject DNA into their bacterial host. The tail anatomy of the archetypal Siphoviridae lambda has been well studied, in contrast to phages infecting gram-positive bacteria. This report outlines a detailed anatomical description of a typical member of the Siphoviridae infecting a gram-positive bacterium. The tail superstructure of the lactococcal phage Tuc2009 was investigated using N-terminal protein sequencing, Western blotting, and immunogold transmission electron microscopy, allowing a tangible path to be followed from gene sequence through encoded protein to specific architectural structures on the Tuc2009 virion. This phage displays a striking parity with lambda with respect to tail structure, which reenforced a model proposed for Tuc2009 tail architecture. Furthermore, comparisons with lambda and other lactococcal phages allowed the specification of a number of genetic submodules likely to encode specific tail structures.

Electrophoresis, Polyacrylamide Gel↗
PubMed1965

Multiple-Tailed T4 Bacteriophage.

Smith, Kendall O. (Baylor University College of Medicine, Houston, Tex.), and Melvin Trousdale. Multiple-tailed T4 bacteriophage. J. Bacteriol. 90:796-802. 1965.-T4 phage particles which appeared to have multiple-tails were observed. Experiments were designed to minimize the possibility that superimposed particles might account for this appearance. Double-tailed particles occurred at a frequency as high as 10%. Triple- and quadruple-tailed particles were extremely rare. All attempts to isolate pure lines of multiple-tailed phage have failed. Multiple-tailed phage particles were produced in highest frequency by Escherichia coli cells in the logarithmic growth phase which had been inoculated at a multiplicity of about 2.

Journal Article↗
PubMed2006

The cytoplasmic tail of the influenza A virus M2 protein plays a role in viral assembly.

The viral replication cycle concludes with the assembly of viral components to form progeny virions. For influenza A viruses, the matrix M1 protein and two membrane integral glycoproteins, hemagglutinin and neuraminidase, function cooperatively in this process. Here, we asked whether another membrane protein, the M2 protein, plays a role in virus assembly. The M2 protein, comprising 97 amino acids, possesses the longest cytoplasmic tail (54 residues) of the three transmembrane proteins of influenza A viruses. We therefore generated a series of deletion mutants of the M2 cytoplasmic tail by reverse genetics. We found that mutants in which more than 22 amino acids were deleted from the carboxyl terminus of the M2 tail were viable but grew less efficiently than did the wild-type virus. An analysis of the virions suggested that viruses with M2 tail deletions of more than 22 carboxy-terminal residues apparently contained less viral ribonucleoprotein complex than did the wild-type virus. These M2 tail mutants also differ from the wild-type virus in their morphology: while the wild-type virus is spherical, some of the mutants were filamentous. Alanine-scanning experiments further indicated that amino acids at positions 74 to 79 of the M2 tail play a role in virion morphogenesis and affect viral infectivity. We conclude that the M2 cytoplasmic domain of influenza A viruses plays an important role in viral assembly and morphogenesis.

Amino Acid Sequence↗
PubMed2006

Distinct domains of the influenza a virus M2 protein cytoplasmic tail mediate binding to the M1 protein and facilitate infectious virus production.

The cytoplasmic tail of the influenza A virus M2 protein is highly conserved among influenza A virus isolates. The cytoplasmic tail appears to be dispensable with respect to the ion channel activity associated with the protein but important for virus morphology and the production of infectious virus particles. Using reverse genetics and transcomplementation assays, we demonstrate that the M2 protein cytoplasmic tail is a crucial mediator of infectious virus production. Truncations of the M2 cytoplasmic tail result in a drastic decrease in infectious virus titers, a reduction in the amount of packaged viral RNA, a decrease in budding events, and a reduction in budding efficiency. The M1 protein binds to the M2 cytoplasmic tail, but the M1 binding site is distinct from the sequences that affect infectious virus particle formation. Influenza A virus strains A/Udorn/72 and A/WSN/33 differ in their requirements for M2 cytoplasmic tail sequences, and this requirement maps to the M1 protein. We conclude that the M2 protein is required for the formation of infectious virus particles, implicating the protein as important for influenza A virus assembly in addition to its well-documented role during virus entry and uncoating.

Amino Acid Sequence↗
PubMed1998

Elongation of the cytoplasmic tail interferes with the fusion activity of influenza virus hemagglutinin.

The hemagglutinin (HA) of fowl plague virus was lengthened and shortened by site-specific mutagenesis at the cytoplasmic tail, and the effects of these modifications on HA functions were analyzed after expression from a simian virus 40 vector. Elongation of the tail by the addition of one to six histidine (His) residues did not interfere with intracellular transport, glycosylation, proteolytic cleavage, acylation, cell surface expression, and hemadsorption. However, the ability to induce syncytia at a low pH decreased dramatically depending on the number of His residues added. Partial fusion (hemifusion), assayed by fluorescence transfer from octadecylrhodamine-labeled erythrocyte membranes, was also reduced, but even with the mutant carrying six His residues, significant transfer was observed. However, when the formation of fusion pores was examined with hydrophilic fluorescent calcein, transfer from erythrocytes to HA-expressing cells was not observed with the mutant carrying six histidine residues. The addition of different amino acids to the cytoplasmic tail of HA caused an inhibitory effect similar to that caused by the addition of His. On the other hand, a mutant lacking the cytoplasmic tail was still able to fuse at a reduced level. These results demonstrate that elongation of the cytoplasmic tail interferes with the formation and enlargement of fusion pores. Thus, the length of the cytoplasmic tail plays a critical role in the fusion process.

Amino Acids↗
PubMed2001

Deletion of the cytoplasmic tail of the fusion protein of the paramyxovirus simian virus 5 affects fusion pore enlargement.

The fusion (F) protein of the paramxyovirus simian parainfluenza virus 5 (SV5) promotes virus-cell and cell-cell membrane fusion. Previous work had indicated that removal of the SV5 F protein cytoplasmic tail (F Tail- or FDelta19) caused a block in fusion promotion at the hemifusion stage. Further examination has shown that although the F Tail- mutant is severely debilitated in promotion of fusion as measured by using two reporter gene assays and is debilitated in the formation of syncytia relative to the wild-type F protein, the F Tail- mutant is capable of promoting the transfer of small aqueous dyes. These data indicate that F Tail- is fully capable of promoting formation of small fusion pores. However, enlargement of fusion pores is debilitated, suggesting that either the cytoplasmic tail of the F protein plays a direct role in pore expansion or that it interacts with other components which control pore growth.

Animals↗
PubMed2001

Vaccinia virus intracellular movement is associated with microtubules and independent of actin tails.

Two mechanisms have been proposed for the intracellular movement of enveloped vaccinia virus virions: rapid actin polymerization and microtubule association. The first mechanism is used by the intracellular pathogens Listeria and Shigella, and the second is used by cellular vesicles transiting from the Golgi network to the plasma membrane. To distinguish between these models, two recombinant vaccinia viruses that express the B5R membrane protein fused to enhanced green fluorescent protein (GFP) were constructed. One had Tyr(112) and Tyr(132) of the A36R membrane protein, which are required for phosphorylation and the nucleation of actin tails, conservatively changed to Phe residues; the other had the A36R open reading frame deleted. Although the Tyr mutant was impaired in Tyr phosphorylation and actin tail formation, digital video and time-lapse confocal microscopy demonstrated that virion movement from the juxtanuclear region to the periphery was saltatory with maximal speeds of >2 microm/s and was inhibited by the microtubule-depolymerizing drug nocodazole. Moreover, this actin tail-independent movement was indistinguishable from that of a control virus with an unmutated A36R gene and closely resembled the movement of vesicles on microtubules. However, in the absence of actin tails, the Tyr mutant did not induce the formation of motile, virus-tipped microvilli and had a reduced ability to spread from cell to cell. The deletion mutant was more severely impaired, suggesting that the A36R protein has additional roles. Optical sections of unpermeabilized, B5R antibody-stained cells that expressed GFP-actin and were infected with wild-type vaccinia virus revealed that all actin tails were associated with virions on the cell surface. We concluded that the intracellular movement of intracellular enveloped virions occurs on microtubules and that the motile actin tails enhance extracellular virus spread to neighboring cells.

Actins↗
PubMed2005

The core histone N-terminal tail domains negatively regulate binding of transcription factor IIIA to a nucleosome containing a 5S RNA gene via a novel mechanism.

Reconstitution of a DNA fragment containing a 5S RNA gene from Xenopus borealis into a nucleosome greatly restricts binding of the primary 5S transcription factor, TFIIIA. Consistent with transcription experiments using reconstituted templates, removal of the histone tail domains stimulates TFIIIA binding to the 5S nucleosome greater than 100-fold. However, we show that tail removal increases the probability of 5S DNA unwrapping from the core histone surface by only approximately fivefold. Moreover, using site-specific histone-to-DNA cross-linking, we show that TFIIIA binding neither induces nor requires nucleosome movement. Binding studies with COOH-terminal deletion mutants of TFIIIA and 5S nucleosomes reconstituted with native and tailless core histones indicate that the core histone tail domains play a direct role in restricting the binding of TFIIIA. Deletion of only the COOH-terminal transcription activation domain dramatically stimulates TFIIIA binding to the native nucleosome, while further C-terminal deletions or removal of the tail domains does not lead to further increases in TFIIIA binding. We conclude that the unmodified core histone tail domains directly negatively influence TFIIIA binding to the nucleosome in a manner that requires the C-terminal transcription activation domain of TFIIIA. Our data suggest an additional mechanism by which the core histone tail domains regulate the binding of trans-acting factors in chromatin.

Animals↗
PubMed1990

Altered baroreflex function after tail suspension in the conscious rat.

Experiments were performed on conscious chronically instrumented rats to determine the contribution of peripheral V2-vasopressinergic receptors in any alteration of baroreceptor reflex (BRR) sensitivity on release from 1 wk of 30 degrees head-down tilt resulting from tail suspension. Initial experiments determined changes in plasma volume (PV) occurring over this period by use of the Evans Blue dye dilution technique. PV was determined immediately before tail suspension and on day 7 of the stimulus. PV, erythrocyte volume, and total blood volume were all significantly diminished on day 7, whereas hematocrit was unchanged. Other rats were instrumented with pulsed Doppler flow probes on the ascending aorta for determination of cardiac output and with arterial and venous catheters 7-10 days before study. Immediately before tail suspension, control cardiac output, mean arterial blood pressure, and heart rate values were determined. In addition, BRR sensitivity was estimated both before and after intravenous administration of a V2-receptor antagonist by assessing the slope of the pulse interval-mean arterial blood pressure relationship in response to a series of pressor doses of phenylephrine. BRR sensitivity was determined on the last day of head-down tilt, 1 min after release from tail suspension, and 10 min after administration of a specific V2-vasopressinergic antagonist. BRR sensitivity tended to fall on day 7 of tail suspension compared with control and was significantly increased after release. However, BRR sensitivity was not altered by intravenous V2 antagonist administration either before tail suspension or after release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Human tail with noncontiguous intraspinal lipoma and spinal cord tethering: case report and embryologic discussion.

Children born with a tail-like appendage have a rare malformation that is frequently associated with abnormalities of the spine and spinal cord. A contiguous fibrolipoma is usually seen extending from the subcutaneous portion of the tail into the inferior spinal cord, resulting in tethered cord syndrome. We present the case of a child born with a tail and intraspinal lipoma that were not contiguous with each other, and were separated by an intact layer of lumbosacral fascia. The tail and lipoma were removed and the spinal cord untethered, and the child is neurologically normal 2 years after surgery. The absence of a contiguous lipoma from the tail to the spinal cord suggests that this condition may be principally caused by a disorder of secondary neurulation and/or regression of the normal embryonic tail bud. The embryology of the lower spine is reviewed and possible etiologies discussed.

Female↗
PubMed2004

Serine residues 338 and 339 in the carboxyl-terminal tail of the type II gonadotropin-releasing hormone receptor are critical for beta-arrestin-independent internalization.

Cloned mammalian type II GnRH receptors have a carboxyl-terminal tail in contrast to the mammalian type I GnRH receptors, which uniquely lack a carboxyl-terminal tail. Because this domain mediates internalization of many serpentine receptors, the internalization pathway of the marmoset monkey type II GnRH receptor and the functional role of the carboxyl-terminal tail in internalization was studied. The internalization pathway of the type II GnRH receptor was investigated in COS-1 cells by coexpressing G protein-coupled receptor kinases (GRKs), dynamin-1, and beta-arrestins. Internalization of the receptor requires GRKs and dynamin but does not require beta-arrestin. The type II GnRH receptor can also internalize via beta-arrestin in the presence of exogenous beta-arrestins, suggesting that the receptor can use two distinct internalization pathways. Receptor internalization appears to occur via clathrin-coated pits and caveolae because disruption of either structure inhibits internalization. Progressive truncations of the carboxyl-terminal tail identified a region containing serine residues 338 and 339 as critical for receptor internalization. Substitution of these serine residues with alanine residues inhibited internalization, whereas substitutions with glutamic acid residues rescued internalization. Furthermore, a dominant-negative GRK2 did not inhibit internalization of receptors having these serine substitutions, although it inhibited internalization of the wild-type receptor. These results together identify serine residues 338 and 339 in the carboxyl-terminal tail as critical for internalization of the type II GnRH receptor and suggest that these residues undergo phosphorylation by GRKs. However, neither of these residues, nor the carboxyl-terminal tail, is required for beta-arrestin-dependent internalization.

Amino Acid Sequence↗