Envelope Processing Research Articles

Modulation masking of lateralization based on envelope interaural phase differences

Modulation-filterbank models discard envelope phase above very low modulation rates. To evaluate the role of relative phase in binaural envelope processing, modulation masking of envelope-based lateralization was measured with a left/right task. A diotic 400-ms wideband noise was modulated by a two-tone function. An interaural phase difference was applied to the probe component of the modulator with the masker component always diotic. The probe modulation rate was 80, 160, or 320 Hz with masker rate varying from 40 to 1280 Hz. Masker modulation interfered with probe lateralization at all probe rates. With 80-Hz probe modulation, the masking function was asymmetric with maskers above the probe more effective than those below. At the higher probe modulation rates, interference was generally greatest when the probe and masker rates were close. However, function asymmetry persisted at these higher rates. In some conditions, a diotic phase shift of the masker had a significant effect. Unlike monaural results, binaural envelope processing showed high-rate phase sensitivity and asymmetric tuning. The asymmetric results and masker-phase effects are consistent with viewing the envelope manipulations as interaural gating asynchronies described by group delay in the modulation domain. [Work supported by NIH.]

Epidemiologic Investigations of Bioterrorism-Related Anthrax, New Jersey, 2001

At least four Bacillus anthracis–containing envelopes destined for New York City and Washington, D.C., were processed at the Trenton Processing and Distribution Center (PDC) on September 18 and October 9, 2001. When cutaneous anthrax was confirmed in a Trenton postal worker, the PDC was closed. Four cutaneous and two inhalational anthrax cases were identified. Five patients were hospitalized; none died. Four were PDC employees; the others handled or received mail processed there. Onset dates occurred in two clusters following envelope processing at the PDC. The attack rate among the 170 employees present when the B. anthracis–containing letters were sorted on October 9 was 1.2%. Of 137 PDC environmental samples, 57 (42%) were positive. Five (10%) of 50 local post offices each yielded one positive sample. Cutaneous or inhalational anthrax developed in four postal employees at a facility where B. anthracis–containing letters were processed. Cross-contaminated mail or equipment was the likely source of infection in two other case-patients with cutaneous anthrax.

Interhelical interactions in the gp41 core: implications for activation of HIV-1 membrane fusion.

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein complex (gp120-gp41) promotes viral entry by mediating the fusion of viral and cellular membranes. Formation of a stable trimer-of-hairpins structure in the gp41 ectodomain brings the two membranes into proximity, leading to membrane fusion. The core of this hairpin structure is a six-helix bundle in which three carboxyl-terminal outer helices pack against an inner trimeric coiled coil. Here we investigate the role of these conserved interhelical interactions on the structure and function of both the envelope glycoprotein and the gp41 core. We have replaced each of the eight amino acids at the buried face of the carboxyl-terminal helix with a representative amino acid, alanine. Structural and physicochemical characterization of the alanine mutants shows that hydrophobic interactions are a dominant factor in the stabilization of the six-helix bundle. Alanine substitutions at the Trp628, Trp631, Ile635, and Ile642 residues also affected envelope processing and/or gp120-gp41 association and abrogated the ability of the envelope glycoprotein to mediate cell-cell fusion. These results suggest that the amino-terminal region of the gp41 outer-layer alpha-helix plays a key role in the sequence of events associated with HIV-1 entry and have implications for the development of antibodies and small-molecule inhibitors of this conserved element.

Auditory temporal envelope processing in a patient with left-hemisphere damage

Auditory temporal envelope processing in a patient with left-hemisphere damage

Auditory Temporal Envelope Processing in a Patient with Left-hemisphere Damage

Abstract Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.

Temporal envelope processing in developmental dyslexics

This study evaluates temporal-envelope processing in six dyslexic children (mean age: 10.10 years), six normal control children (11.6 years), and six normal control adults (24.8 years) by measuring: (1) temporal modulation transfer functions (TMTFs), i.e., the detection thresholds of sinusoidal amplitude-modulation applied to a white noise carrier, as a function of modulation frequency (4, 16, 64, 256, or 1024 Hz), (2) recognition performance for vowel-consonant-vowel stimuli over five sessions; speech stimuli were either unprocessed or processed to degrade the spectral information. Modulation thresholds were similar in normal children and adults; for both groups, TMTFs were low pass in shape. TMTFs measured in dyslexics were bandpass in four children, low pass and flat in the two others. Overall, modulation thresholds were higher in dyslexics than in normal children at 4 and 1024 Hz. Unprocessed-speech recognition performance was perfect in normal children and adults, and impaired in dyslexics. Processed-speech recognition performance was poorer in normal and dyslexic children compared to normal adults. Performance improved across sessions in normal children and adults, but remained constant in dyslexics. These results support the hypothesis that some dyslexics show abnormal auditory temporal-envelope processing. This may, in turn, explain their difficulties with speech perception. [Work supported by the Cognitique program.]

Auditory temporal envelope processing in a patient with left-hemisphere damage

Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.

Amplitude-modulation detection in two patients with left- or right-hemisphere damage

The modulation depth required for the detection of sinusoidal amplitude-modulation applied to a white noise carrier was measured as a function of modulation frequency, giving temporal modulation transfer functions (TMTFs). The modulation frequency was 4, 16, 64, 256, or 1024 Hz. Measurements of intensity discrimination thresholds for white noise were performed as a control task. In both tasks, white noise stimuli had a 2-s duration and were presented monaurally at 75 dB SPL. Two adult listeners with left- or right-hemisphere damage and three normal-control adult listeners were tested in each ear. Lesions encompassed the primary auditory cortex in the two patients. All listeners had normal audiometric thresholds. The modulation detection data showed no sign of ear asymmetry. For all listeners, the TMTFs displayed a typical low-pass characteristic. Modulation detection was 10–14 dB poorer-than-normal at modulation frequencies between 4 and 256 Hz in the patient with left-hemisphere damage. In contrast, modulation detection was normal in the patient with right-hemisphere damage. Intensity discrimination was within the normal range (0.5–1 dB) for both patients. These results support the hypothesis that cortical structures within the left hemisphere play a crucial role in temporal envelope processing. [Work supported by the Fondation de l’Avenir and the Cognitique Program.]

Abundant defective viral particles budding from microglia in the course of retroviral spongiform encephalopathy.

A pathogenetic hallmark of retroviral neurodegeneration is the affinity of neurovirulent retroviruses for microglia cells, while degenerating neurons are excluded from retroviral infections. Microglia isolated ex vivo from rats peripherally infected with a neurovirulent retrovirus released abundant mature type C virions; however, infectivity associated with microglia was very low. In microglia, viral transcription was unaffected but envelope proteins were insufficiently cleaved into mature viral proteins and were not detected on the microglia cell surface. These microglia-specific defects in envelope protein translocation and processing not only may have prevented formation of infectious virus particles but also may have caused further cellular defects in microglia with the consequence of indirect neuronal damage. It is conceivable that similar events play a role in neuro-AIDS.

Engineering of Noninfectious HIV-1-like Particles Containing Mutant gp41 Glycoproteins as Vaccine Candidates That Allow Vaccinees to Be Distinguished from HIV-1 Infectees

Many AIDS vaccine candidates under development may elicit immune responses similar to those observed in and used to screen human immunodeficiency virus type 1 (HIV-1)-infected individuals. Therefore, it is important to develop vaccine candidates that incorporate antigenic markers and allow vaccinees to be distinguished from HIV-1 infectees. To this end, we introduced a series of mutations into and in the vicinity of the major immunodominant region (MIR) of gp41 (residues 598–609), a domain recognized by almost all HIV-1 infectees, and evaluated whether HIV-1-like particles incorporating such mutant glycoproteins could be expressed in mammalian cells. Results indicated that although up to three consecutive amino acids could be replaced within MIR without significantly affecting particle formation or gp160 processing, deletions within MIR impaired envelope processing. Replacement of HIV-1 MIR by part or most of the corresponding domain from other lentiviruses markedly decreased or abolished gp160 processing. Synthetic peptides corresponding to a mutated MIR incorporating three amino acid replacements were not recognized by a panel of sera from HIV-1 infectees, suggesting that HIV-1-like particles with this type of mutation represent potential candidate vaccines that could allow vaccinees to be distinguished from HIV-1 infectees.

Analysis of HTLV-II syncytium formation using recombinant cowpoxvirus expressing the evelope precursor glycoprotein,gp63.

P171 Infection by human T lymphotropic viruses type I and type II (HTLV-I and HTLV-II) results in cell membrane fusion or syncytium formation in vitro. The development of syncytium is considered to correlate with the susceptibility of cells to virus infection, and specifically with the interaction of the cellular receptor and the virus envelope glycoprotein. To investigate mechanisms of cell membrane fusion we have constructed a recombinant cowpoxvirus which permits expression of the HTLV-II envelope precursor glycoprotein, and have examined syncytia formation in a range of mammalian cell lines using an assay employing recombinant cowpoxvirus allowing the expression of HTLV-II envelope and the vaccinia virus T7 RNA polymerase, and a plasmid expressing β-gal under control of the T7 promoter. In this system, only cells fused with target cells turn the color blue, so that cell fusion can be detected with great sensitivity. Employing cell lines of human, mouse, rat, and monkey origin, although there was great variation almost all formed syncytia. We also investigated the levels of envelope glycoprotein expression and processing in cells exhibiting different degrees of syncytia formation using Western blotting methods. A clone of the monkey kidney cell line CV-1 which rarely and only poorly developed syncytia was found to have high levels of precursor glycoprotein gp63 expression and low levels of processing to gp46. Conversely cell lines which readily developed syncytia were found to have increased levels of gp46. We conclude that the cellular receptor for HTLV-II infection is widely distributed among different species and cell types, and that processing of the envelope precursor glycoprotein gp63 to gp46 and gp21 is necessary for the development of syncytia.

Robust and reliable epicenter determinations: Envelope processing of local network data

Abstract Local event recordings are complex in the sense that relevant P and S phases vary in an unpredictable manner even between closely spaced stations; thus, manual analysis of such records is still commonplace. Our approach to solving this long-standing problem of observational seismology is to bandpass filter (3 to 6 Hz) to ensure good signal-to-noise ratio SNR and then form envelopes to ensure simple signals across a seismograph network. The physical basis is that Pg and Lg are crustal wave-guide phases reflecting P- and S-energy propagation. Extensive tests on envelope analysis of local records from different areas found that arrival times of the maxima of Pg and Lg envelopes increase very consistently with distance even in different tectonic regimes, typical velocities being 6.1 and 3.5 km/sec, respectively. These arrival-time parameters are easy to extract in a semi-automatic manner and are highly suitable for local epicenter determinations. Extensive tests on locating mining explosions were conducted, and on average, the “envelope” location errors relative to “true” locations were similar to those in bulletins that are based on conventional phase pickings. Occasionally, the Pg/Pn envelope may be very weak but can be replaced by the easily pickable (non-envelope) Pn phase. Additional advantages with envelope locations are transportability (not overly sensitive to details of crustal structure), and that envelope amplitudes can be directly converted to ground motion and magnitudes. For modern stations, envelopes can be formed in situ with low sampling rates of 1 to 2 Hz, thus greatly reducing transmission costs.

Definition of a 14-amino-acid peptide essential for the interaction between the murine leukemia virus amphotropic envelope glycoprotein and its receptor.

Hydrophilic loops in the receptor binding domain of the amphotropic murine leukemia virus (MLV) envelope glycoprotein (SU) are predicted and may participate in SU-receptor interactions. We have replaced five segments of 6 to 15 amino acids located in each of these regions with an 11-amino-acid tag from the vesicular stomatitis virus glycoprotein (VSV-G). Substitution was compatible with envelope processing, transport, and incorporation into virions. However, three substitution mutants showed a temperature-dependent phenotype, suggesting structural unstability. Accessibility of the tagging epitope for a monoclonal anti-VSV-G antibody was greater in oligomeric than in monomeric SUs when insertion was done in VRA, a domain essential for receptor recognition. In contrast, accessibility was independent of structural constraints when insertion was done in VRB, a domain playing an accessory role in receptor binding. Interaction with the amphotropic receptor was investigated by interference assay and study of binding and infection of target cells with MLV particles coated with the substituted envelopes. Envelope-receptor interaction was abolished when substitution was performed in a potential loop-forming segment located at the N-terminal half of VRA. Although interaction was affected to variable extents, depending on the substituted segment, other mutants conserved the ability to interact with the amphotropic receptor. These experiments indicate the 14-amino-acid segment between positions 50 and 64 of SU as an essential determinant of amphotropic-receptor recognition. They also show that a foreign linear epitope can be tolerated in several locations of the amphotropic SU receptor binding site, and this result has implications for the design of targeted retroviral vectors.

The psychophysics of complex envelope processing

During the past decade, psychophysical research on the processing of amplitude modulation (AM) has expanded to relatively complex situations where subjects are asked to make detection or discrimination judgments regarding some aspect of AM in the presence of competing AM. This AM-masking paradigm has been referred to as modulation masking when the signal and masker carriers are overlapping noise bands, and as modulation detection (or discrimination) interference (MDI) when the two carriers are sinusoids. An important finding in the MDI paradigm is that this AM masking occurs even when the sinusoidal carriers are 2 or more oct apart, and hence under conditions where peripheral interactions within a single auditory filter are unlikely. It also occurs when the signal and masker carriers are presented to opposite ears, further evidence that at least some of the AM masking is occurring at a relatively central site in the auditory system. Finally, a common finding in these masking experiments is a rather broad tuning for the detection (or discrimination) of AM. Whether this turning should be taken as evidence for AM channels in the auditory system will be discussed, as will recent research on subjects with cochlear hearing loss. [Work supported by NIDCD.]

Structural analysis of the principal immunodominant domain of the feline immunodeficiency virus transmembrane glycoprotein.

In the transmembrane envelope glycoprotein (TM) of lentiviruses, including human immunodeficiency virus type 1 (HIV-1) and feline immunodeficiency virus (FIV), two cysteine residues, conserved in most retroviruses, are thought to form a loop containing five to seven amino acids. These elements make up a B-cell epitope recognized by nearly 100% of sera from infected patients or animals, designated the principal immunodominant domain (PID). The PID amino acid sequences are highly conserved between isolates of the same lentivirus but are unrelated, except for the two cysteines, when divergent lentiviruses are compared. The aim of this study was to analyze the relationship between amino acid sequence in the PID and envelope function. We introduced two kinds of mutations in the PID of FIV: mutations which impeded the formation of a loop and mutations which substituted the sequence of FIV with the corresponding sequences from other lentiviruses, HIV-1, visna virus, and equine infectious anemia virus. We analyzed antibody recognition, processing, and fusogenic properties of the modified envelopes, using two methods of Env expression: a cell-free expression system and transfection of a feline fibroblast cell line with gag-pol-deleted FIV proviruses. Most mutations in the PID of FIV severely affected envelope processing and abolished syncytium formation. Only the chimeric envelope containing the HIV-1 PID sequence was correctly processed and maintained the capacity to induce syncytium formation, although less efficiently than the wild-type envelope. We computed three-dimensional structural models of the PID, which were consistent with mutagenesis data and confirmed the similarity of FIV and HIV-1 PID structures, despite their divergence in amino acid sequence. Considering these results, we discussed the respective importance of selection exerted by functional requirements or host antibodies to explain the observed variations of the PIDs in lentiviruses.

Propensity for a leucine zipper-like domain of human immunodeficiency virus type 1 gp41 to form oligomers correlates with a role in virus-induced fusion rather than assembly of the glycoprotein complex.

For a number of viruses, oligomerization is a critical component of envelope processing and surface expression. Previously, we reported that a synthetic peptide (DP-107) corresponding to the putative leucine zipper region (aa 553-590) of the transmembrane protein (gp41) of human immunodeficiency virus type 1 (HIV-1) exhibited alpha-helical secondary structure and self-associated as a coiled coil. In view of the tendency of this type of structure to mediate protein association, we speculated that this region of gp41 might play a role in HIV-1 envelope oligomerization. However, later it was shown that mutations which should disrupt the structural elements of this region of gp41 did not affect envelope processing, transport, or surface expression (assembly oligomerization). In this report we compare the effects of amino acid substitutions within this coiled-coil region on structure and function of both viral envelope proteins and the corresponding synthetic peptides. Our results establish a correlation between the destabilizing effects of amino acid substitutions on coiled-coil structure in the peptide model and phenotype of virus entry. These biological and physical biochemical studies do not support a role for the coiled-coil structure in mediating the assembly oligomerization of HIV-1 envelope but do imply that this region of gp41 plays a key role in the sequence of events associated with viral entry. We propose a functional role for the coiled-coil domain of HIV-1 gp41.

Discrimination of envelope frequency in one spectral region in the presence of modulation in another

This paper examines how discrimination of envelope frequency in one spectral region is affected by the presence of either correlated or uncorrelated modulation in another spectral region. Envelope-frequency discrimination thresholds, delta fe's, for a 60-dB SPL two-tone complex centered at 2 kHz were measured in the presence or absence of an auxiliary two-tone complex at another frequency. When present, the auxiliary complex had either the same envelope as the standard signal or an envelope that was uncorrelated with both the standard and variable signal. The results show that listeners can take advantage of correlation between simultaneous envelopes in different frequency regions to improve discrimination of a small change in envelope frequency, whereas the presence of uncorrelated envelopes causes interference with discrimination. Except when the auxiliary complex and the signal are close together in frequency, the discrimination advantage afforded by the correlated auxiliaries appears to reflect across-channel envelope processing. The discrimination interference caused by the uncorrelated auxiliaries, on the other hand, may reflect primarily within-channel interaction such as peripheral masking, although a small amount of across-channel masking also is apparent.

Reproducible noise discrimination with concurrent narrowband noises

Reproducible noise discrimination ability was measured with a cued 2IFC procedure. Stimuli were either one, two, or three concurrent noise bands with bandwidths of either 12.5, 50, or 200 Hz and center frequencies of either 500, 1250, or 3125 Hz. In the multiband conditions, the concurrent noise samples either shared a common bandwidth and a common pattern of envelope fluctuation, had a common bandwidth with asynchronous envelopes, or had different bandwidths. Performance in the single versus multiband conditions was used to estimate cross-spectral correlations in the integration of envelope information. Single-band d′’s were inversely related to both bandwidth and center frequency. Performance in the multiband conditions was generally better than with the component bands presented individually. For subjects whose single-band d′’s were widely separated, greatest integration was obtained in the synchronous multiband conditions. Correlation estimates were significantly higher in the synchronous versus the two asynchronous condition sets. In all conditions, estimated correlation was inversely related to bandwidth. Results are used to model internal noise levels in cross-spectral envelope processing. [Work supported by NIH.]

Structure and Expression of the Human T-Cell Leukemia Virus Type 1 Envelope Protein

The structure and expression of the HTLV-1 envelope protein was examined using T lymphoid cell lines infected with HTLV-1 and recombinant vaccinia viruses expressing the HTLV-1 envelope. Pulse-chase experiments demonstrated that the envelope precursor, gp62, had a half-life of 7-12 hr. N-glycosylation of the precursor protein was examined using tunicamycin and endoglycosidase H. These studies revealed that at least four and possibly five potential N-glycosylation sites were utilized. In addition, the envelope precursor was found to sediment on sucrose gradients as high-molecular-weight complexes, in positions consistent with the formation of dimers and smaller amounts of higher multimeric forms. Finally, the recombinant vaccinia system was used to express mutants designed to analyze the role in HTLV-1 envelope processing of the cytoplasmic tail and the membrane-spanning domain.

Analysis of chloroplast transit peptide function using mutations in the carboxyl-terminal region

Protein import into chloroplasts requires a transit peptide, which interacts with the chloroplast transport apparatus and leads to translocation of the protein across the chloroplast envelope. While the amino acid sequences of many transit peptides are known, functional domains have been difficult to identify. Previous studies suggest that the carboxyl terminus of the transit peptide for ribulose bisphosphate carboxylase small subunit is important for both translocation across the chloroplast envelope and proper processing of the precursor protein. We dissected this region using in vitro mutagenesis, creating a set of mutants with small changes in primary structure predicted to cause alterations in secondary structure. The import behavior of the mutant proteins was assessed using isolated chloroplasts. Our results show that removal of a conserved arginine residue in this region results in impaired processing, but does not necessarily affect import rates. In contrast, substituting amino acids with low reverse turn or amphiphilic potential for other original residues affected import rate but not processing.