RESUMEN
BACKGROUND: C-reactive protein (CRP) is an acute-phase protein produced by the liver during systemic inflammation. In humans, some epilepsies are associated with increased serum CRP (sCRP) concentrations, but this has yet to be proven in veterinary studies. Dogs with structural epilepsy (SE) and normal interictal neurological examination are hard to distinguish from dogs with idiopathic epilepsy (IE) without the use of advanced imaging. METHODS: The study included eight dogs with SE and 12 dogs with IE from a referral hospital population. This was a retrospective observational cohort study. The Mann-Whitney test was used to compare the sCRP concentrations within 24 hours of the last epileptic seizure between dogs with SE or IE. RESULTS: Dogs with SE had higher sCRP concentrations than dogs with IE (8.9 [range <2.2-53.2] mg/L vs. <2.2 [range <2.2-6.9] mg/L; p = 0.043). Five of the eight (62%) dogs with SE had an sCRP concentration above the reference interval, compared with none of the 12 dogs with IE. LIMITATIONS: The small sample size was the major limitation of this study. Other inflammatory causes were also not exclusively ruled out, although further clinical investigations were not indicated. CONCLUSIONS: This study found that sCRP concentrations were higher in this cohort of dogs with SE than in those with IE. Further studies with larger cohorts of dogs are warranted to validate if sCRP can be used as an additional biomarker for SE.
Asunto(s)
Enfermedades de los Perros , Epilepsia , Humanos , Perros , Animales , Proteína C-Reactiva/metabolismo , Estudios de Cohortes , Enfermedades de los Perros/etiología , Epilepsia/veterinaria , Epilepsia/diagnóstico , Convulsiones/veterinariaRESUMEN
Case summary: A 2-year-old male neutered domestic shorthair cat was referred for investigation of a 10-month history of self-limiting, generalised tonic-clonic seizures. The cat was reported to be normal interictally but had always had a static abnormal gait. General physical examination was unremarkable. Neuroanatomical localisation was compatible with a diffuse cerebellar and diffuse forebrain lesion. Complete blood count, biochemistry, bile acid stimulation test, urinalysis, cisternal cerebrospinal fluid (CSF) analysis, Toxoplasma gondii serology and T gondii polymerase chain reaction in CSF were all unremarkable. MRI revealed an abnormal caudal fossa, absent cerebellar vermis and small cerebellar hemisphere with distension of the fourth ventricle. There were no forebrain abnormalities identified in the MRI or CSF changes that could justify the seizures. Considering the clinical presentation, the cat's neurological examination and MRI features, a presumptive diagnosis of Dandy Walker-like malformation (DWLM) and epilepsy of unknown aetiology was made. Relevance and novel information: This is the first case report of an adult cat diagnosed with cerebellar malformation resembling DWLM and concomitant seizures, its MRI characteristics and long-term follow-up. The 3-year follow-up consultation revealed static neurological status with 2-4 seizures per year. The cat's quality of life remained good at the time of writing.
RESUMEN
The ability to differentiate clinical ventriculomegaly from incidental ventricular enlargement remains a challenge in veterinary radiology. Dilatation of one or both olfactory lobe recesses is occasionally seen on MRI of the brain in otherwise normal cats. The purpose of this study was therefore to determine the prevalence of this finding within a population of neurologically normal and neurologically abnormal cats, and to investigate associations with signalment, clinical and neurological examination findings, and MRI features. An observational retrospective cohort study was performed, and archived records were searched for cats that had undergone MRI of the head, including the olfactory lobes. Medical data and MRI parameters were recorded. One hundred fifty-one cats were included, with olfactory recess dilatation present in 56 cats. In 16 neurologically normal cats, olfactory recess dilatation was the only MRI finding. Olfactory recess dilatation was not associated with age, sex, breed, or with the presence of nasal disease. A significant association was found between generalized ventriculomegaly (P = 0.001) and the presence of CSF abnormalities (P = 0.036). Eleven percent of our cohort (16/151) demonstrated olfactory recess dilatation in the absence of other neurological or structural intracranial disease, suggesting that this may be seen as a normal variation in some cats.
Asunto(s)
Enfermedades de los Gatos , Hidrocefalia , Animales , Gatos , Encéfalo , Enfermedades de los Gatos/diagnóstico por imagen , Enfermedades de los Gatos/epidemiología , Hidrocefalia/veterinaria , Imagen por Resonancia Magnética/veterinaria , Prevalencia , Estudios RetrospectivosRESUMEN
BACKGROUND: Clinicians observe that cats and dogs referred to neurology services often do not have an underlying neurological disorder. There has been no analysis of the frequency or categorisation of these neurological mimics. METHODS: Retrospective study of 520 cases was carried out. Data on signalment, presenting clinical signs, neurological examination findings and final diagnosis were collected. Final diagnoses were classified as primary neurological, non-neurological in origin but with neurological clinical manifestation, completely non-neurological (neurological mimics) or undiagnosed. Presenting clinical signs and neurological examination results were compared between neurological mimics and primary neurological cases using Chi-square or Fischer exact test. Relative risk (RR) was calculated for significant associations. RESULTS: A total of 74% were primary neurological conditions, 8% neurological mimics, 3% non-neurological with neurological manifestation and 15% undiagnosed. An animal referred for lameness was approximately five times more likely to be diagnosed as a neurological mimic than as a primary neurological disorder (RR = 5.42, p < 0.001). Cases with a normal neurological examination were approximately 15 times more likely to be a neurological mimic (RR = 14.97, p < 0.001). CONCLUSION: Thorough examination with consideration of alternative diagnoses is important when a neurological condition is suspected in an animal that presents with lameness or normal neurological examination.
Asunto(s)
Enfermedades de los Gatos , Enfermedades de los Perros , Enfermedades del Sistema Nervioso , Neurología , Animales , Enfermedades de los Gatos/diagnóstico , Gatos , Enfermedades de los Perros/diagnóstico , Perros , Hospitales Veterinarios , Cojera Animal , Enfermedades del Sistema Nervioso/diagnóstico , Enfermedades del Sistema Nervioso/veterinaria , Derivación y Consulta , Estudios RetrospectivosRESUMEN
BACKGROUND: Orthostatic tremor (OT) is a rare movement disorder characterized by high-frequency (>12 Hz) involuntary, rhythmic, sinusoidal movements affecting predominantly the limbs while standing. OBJECTIVE: To describe the signalment, presenting complaints, phenotype, diagnostic findings, treatment, and outcome of a large sample of dogs with OT. ANIMALS: Sixty dogs diagnosed with OT based on conscious electromyography. METHODS: Multicenter retrospective case series study. Dogs were included if they had a conscious electromyography consistent with muscle discharge frequency >12 Hz while standing. RESULTS: Fifty-three cases were diagnosed with primary OT (POT). Giant breed dogs represented most cases (83%; 44/53). Most dogs (79%; 42/53) were younger than 2 years of age at onset of signs, except for Retrievers which were all older than 3.5 years of age. The most common presenting complaints were pelvic limb tremors while standing (85%; 45/53) and difficulty when rising or sitting down (45%; 24/53). Improvement of clinical signs occurred in most dogs (85%; 45/53) treated medically with phenobarbital, primidone, gabapentin, pregabalin or clonazepam, but it was mostly partial rather than complete. Orthostatic tremor-plus was seen in 7 dogs that had concurrent neurological diseases. CONCLUSIONS AND CLINICAL IMPORTANCE: Primary OT is a progressive disease of young, purebred, giant/large-breed dogs, which appears to begin later in life in Retrievers. Primary OT apparently responds partially to medications. Orthostatic tremor-plus exists in dogs and can be concomitant or associated with other neurological diseases.
Asunto(s)
Enfermedades de los Perros , Temblor , Animales , Mareo/veterinaria , Enfermedades de los Perros/tratamiento farmacológico , Perros , Electromiografía/veterinaria , Estudios Retrospectivos , Temblor/tratamiento farmacológico , Temblor/veterinariaRESUMEN
CASE SUMMARY: An 11-year-old neutered male Maine Coon cat was presented for investigation of anisocoria and depression. Neurological examination was consistent with a lesion at the level of the middle cranial fossa, and biochemistry was indicative of moderate renal functional impairment. MRI of the brain identified an extra-axial mass lesion at the level of the middle cranial fossa, T2-weighted hyperintense and strongly homogeneously contrast enhancing with dural tail. The cat was euthanased after 6 weeks of palliative treatment with corticosteroids. Histopathology and immunohistochemistry of the brain, the intra-cranial mass and the renal masses found on necropsy were consistent with histiocytic sarcoma. RELEVANCE AND NOVEL INFORMATION: Central nervous system histiocytic sarcoma is a rare finding in cats. This original case report describes the neurological presentation, novel MRI characteristics and pathological findings of suspected primary histiocytic sarcoma affecting the brain with renal metastasis in a cat.
RESUMEN
BACKGROUND: Hyperproteinorrachia (raised cerebrospinal fluid total protein [CSF-TP]) without pleocytosis (HP) (also known as albuminocytologic dissociation) is identified in dogs with different neurologic diseases. However, the association between survival and increased CSF-TP is unknown. OBJECTIVES: (a) Identify conditions commonly associated with HP in dogs and (b) investigate whether higher CSF-TP concentrations or other relevant factors are associated with 1-year survival. METHODS: This is a retrospective study that identified dogs with HP (Cisternal CSF-TP >0.30 g/L, Lumbar CSF-TP >0.45 g/L with total nucleated cell concentrations [TNCCs] and RBC counts within RIs) from 2008 to 2019: recording signalment, weight, vital parameters, inflammation, neuroanatomic localization, CSF-TP, sampling site, final diagnosis, etiologic classification, and 1-year survival. Corrected CSF-TP was calculated as CSF-TP minus 0.3 (cisternal) or 0.45 (lumbar or unknown). Descriptive statistics were produced, CSF-TP differences between groups (eg, neuroanatomic localizations) were evaluated using the Mann-Whitney U test or Kruskal-Wallis test (post-hoc testing). The Cox proportional hazards model was used for survival data. Statistical significance was set at a P < 0.05. RESULTS: In all, 39 dogs had HP, associated with 17 conditions, including neoplasia (n = 6), meningoencephalitis of unknown origin (n = 4) (MUO), and intervertebral disc disease (n = 4) (IVDD) as the most common conditions. There was no significant difference between the CSF-TP/corrected CSF-TP between 1-year survivors and non-survivors, nor was there a difference between different neuroanatomic localizations or etiologic classifications (P > 0.05). Neoplasia, after adjustment for age, was the only variable associated with a worse survival (P = 0.01 HR: 2.08 (95% CI: 1.65-39.2). CSF-TP was not associated with age (P > 0.05). CONCLUSIONS: HP in dogs is associated with a wide range of conditions; the most common conditions are neoplasia, MUO, and IVDD. Higher CSF-TP levels do not correlate with a worse 1-year survival; however, they do correlate with neoplastic lesions.
Asunto(s)
Enfermedades de los Perros , Degeneración del Disco Intervertebral , Desplazamiento del Disco Intervertebral , Animales , Perros , Degeneración del Disco Intervertebral/veterinaria , Desplazamiento del Disco Intervertebral/veterinaria , Leucocitosis/veterinaria , Estudios RetrospectivosRESUMEN
A 1-year, 8-month-old Rhodesian Ridgeback was presented with obtundation, ambulatory tetraparesis, and myoclonus. Initial clinical findings included ionized hypercalcemia with an apparent marked increase in parathyroid hormone, thrombocytopenia, and nonregenerative anemia. Low numbers of circulating atypical cells were noted on blood film evaluation. Brain magnetic resonance imaging identified an extra-axial contrast enhancing subtentorial lesion, and cerebrospinal fluid (CSF) analysis documented a marked atypical lymphocytic pleocytosis. Flow cytometry performed on the CSF demonstrated expression of only CD45, CD90, and MHC class II, with Pax5 positivity on subsequent immunohistochemistry. The final diagnosis was of B-cell lymphoblastic lymphoma or acute leukemia, given the distribution of disease and the presence of significant bone marrow infiltration alongside an aggressive clinical course. The unusual immunophenotype of the neoplastic cells and hypercalcemia presented antemortem diagnostic challenges, highlighting the need for a multidisciplinary approach and caution in the interpretation of clinical abnormalities in cases with multiple comorbidities.
Asunto(s)
Enfermedades de los Perros/diagnóstico , Hipercalcemia/veterinaria , Linfoma de Células B/veterinaria , Mioclonía/veterinaria , Leucemia-Linfoma Linfoblástico de Células Precursoras/veterinaria , Animales , Linfocitos B/citología , Médula Ósea , Encéfalo/diagnóstico por imagen , Perros , Femenino , Citometría de Flujo/veterinaria , Inmunofenotipificación , Leucocitosis/líquido cefalorraquídeo , Linfoma de Células B/patología , Angiografía por Resonancia Magnética/veterinaria , Leucemia-Linfoma Linfoblástico de Células Precursoras/patologíaRESUMEN
Measles virus (MeV), a highly contagious member of the Paramyxoviridae family, causes measles in humans. The Paramyxoviridae family of negative single-stranded enveloped viruses includes several important human and animal pathogens, with MeV causing approximately 120,000 deaths annually. MeV and canine distemper virus (CDV)-mediated diseases can be prevented by vaccination. However, sub-optimal vaccine delivery continues to foster MeV outbreaks. Post-exposure prophylaxis with antivirals has been proposed as a novel strategy to complement vaccination programs by filling herd immunity gaps. Recent research has shown that membrane fusion induced by the morbillivirus glycoproteins is the first critical step for viral entry and infection, and determines cell pathology and disease outcome. Our molecular understanding of morbillivirus-associated membrane fusion has greatly progressed towards the feasibility to control this process by treating the fusion glycoprotein with inhibitory molecules. Current approaches to develop anti-membrane fusion drugs and our knowledge on drug resistance mechanisms strongly suggest that combined therapies will be a prerequisite. Thus, discovery of additional anti-fusion and/or anti-attachment protein small-molecule compounds may eventually translate into realistic therapeutic options.
Asunto(s)
Virus del Sarampión/fisiología , Proteínas Virales de Fusión/química , Proteínas Virales de Fusión/metabolismo , Antivirales/farmacología , Sitios de Unión , Descubrimiento de Drogas , Interacciones Huésped-Patógeno , Humanos , Sarampión/tratamiento farmacológico , Sarampión/virología , Virus del Sarampión/efectos de los fármacos , Modelos Moleculares , Unión Proteica , Conformación Proteica , Pliegue de Proteína , Dominios y Motivos de Interacción de Proteínas , Multimerización de Proteína , Receptores Virales/química , Receptores Virales/metabolismo , Relación Estructura-Actividad , Inhibidores de Proteínas Virales de Fusión/farmacología , Proteínas Virales de Fusión/antagonistas & inhibidores , Internalización del VirusRESUMEN
Despite large vaccination campaigns, measles virus (MeV) and canine distemper virus (CDV) cause major morbidity and mortality in humans and animals, respectively. The MeV and CDV cell entry system relies on two interacting envelope glycoproteins: the attachment protein (H), consisting of stalk and head domains, co-operates with the fusion protein (F) to mediate membrane fusion. However, how receptor-binding by the H-protein leads to F-triggering is not fully understood. Here, we report that an anti-CDV-H monoclonal antibody (mAb-1347), which targets the linear H-stalk segment 126-133, potently inhibits membrane fusion without interfering with H receptor-binding or F-interaction. Rather, mAb-1347 blocked the F-triggering function of H-proteins regardless of the presence or absence of the head domains. Remarkably, mAb-1347 binding to headless CDV H, as well as standard and engineered bioactive stalk-elongated CDV H-constructs treated with cells expressing the SLAM receptor, was enhanced. Despite proper cell surface expression, fusion promotion by most H-stalk mutants harboring alanine substitutions in the 126-138 "spacer" section was substantially impaired, consistent with deficient receptor-induced mAb-1347 binding enhancement. However, a previously reported F-triggering defective H-I98A variant still exhibited the receptor-induced "head-stalk" rearrangement. Collectively, our data spotlight a distinct mechanism for morbillivirus membrane fusion activation: prior to receptor contact, at least one of the morbillivirus H-head domains interacts with the membrane-distal "spacer" domain in the H-stalk, leaving the F-binding site located further membrane-proximal in the stalk fully accessible. This "head-to-spacer" interaction conformationally stabilizes H in an auto-repressed state, which enables intracellular H-stalk/F engagement while preventing the inherent H-stalk's bioactivity that may prematurely activate F. Receptor-contact disrupts the "head-to-spacer" interaction, which subsequently "unlocks" the stalk, allowing it to rearrange and trigger F. Overall, our study reveals essential mechanistic requirements governing the activation of the morbillivirus membrane fusion cascade and spotlights the H-stalk "spacer" microdomain as a possible drug target for antiviral therapy.
Asunto(s)
Antígenos CD/metabolismo , Moléculas de Adhesión Celular/metabolismo , Modelos Moleculares , Morbillivirus/fisiología , Receptores de Superficie Celular/metabolismo , Proteínas Virales/metabolismo , Internalización del Virus , Sustitución de Aminoácidos , Animales , Anticuerpos Monoclonales/farmacología , Antígenos CD/química , Antígenos CD/genética , Moléculas de Adhesión Celular/química , Moléculas de Adhesión Celular/genética , Chlorocebus aethiops , Virus del Moquillo Canino/metabolismo , Perros , Células HEK293 , Humanos , Fusión de Membrana/efectos de los fármacos , Morbillivirus/efectos de los fármacos , Mutación , Conformación Proteica , Pliegue de Proteína/efectos de los fármacos , Dominios y Motivos de Interacción de Proteínas , Estabilidad Proteica/efectos de los fármacos , Receptores de Superficie Celular/química , Receptores de Superficie Celular/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Miembro 1 de la Familia de Moléculas Señalizadoras de la Activación Linfocitaria , Células Vero , Proteínas Virales/antagonistas & inhibidores , Proteínas Virales/química , Proteínas Virales/genética , Acoplamiento Viral/efectos de los fármacos , Internalización del Virus/efectos de los fármacosRESUMEN
UNLABELLED: Measles and canine distemper viruses (MeV and CDV, respectively) first replicate in lymphatic and epithelial tissues by using SLAM and nectin-4 as entry receptors, respectively. The viruses may also invade the brain to establish persistent infections, triggering fatal complications, such as subacute sclerosis pan-encephalitis (SSPE) in MeV infection or chronic, multiple sclerosis-like, multifocal demyelinating lesions in the case of CDV infection. In both diseases, persistence is mediated by viral nucleocapsids that do not require packaging into particles for infectivity but are directly transmitted from cell to cell (neurons in SSPE or astrocytes in distemper encephalitis), presumably by relying on restricted microfusion events. Indeed, although morphological evidence of fusion remained undetectable, viral fusion machineries and, thus, a putative cellular receptor, were shown to contribute to persistent infections. Here, we first showed that nectin-4-dependent cell-cell fusion in Vero cells, triggered by a demyelinating CDV strain, remained extremely limited, thereby supporting a potential role of nectin-4 in mediating persistent infections in astrocytes. However, nectin-4 could not be detected in either primary cultured astrocytes or the white matter of tissue sections. In addition, a bioengineered "nectin-4-blind" recombinant CDV retained full cell-to-cell transmission efficacy in primary astrocytes. Combined with our previous report demonstrating the absence of SLAM expression in astrocytes, these findings are suggestive for the existence of a hitherto unrecognized third CDV receptor expressed by glial cells that contributes to the induction of noncytolytic cell-to-cell viral transmission in astrocytes. IMPORTANCE: While persistent measles virus (MeV) infection induces SSPE in humans, persistent canine distemper virus (CDV) infection causes chronic progressive or relapsing demyelination in carnivores. Common to both central nervous system (CNS) infections is that persistence is based on noncytolytic cell-to-cell spread, which, in the case of CDV, was demonstrated to rely on functional membrane fusion machinery complexes. This inferred a mechanism where nucleocapsids are transmitted through macroscopically invisible microfusion events between infected and target cells. Here, we provide evidence that CDV induces such microfusions in a SLAM- and nectin-4-independent manner, thereby strongly suggesting the existence of a third receptor expressed in glial cells (referred to as GliaR). We propose that GliaR governs intercellular transfer of nucleocapsids and hence contributes to viral persistence in the brain and ensuing demyelinating lesions.
Asunto(s)
Antígenos CD/metabolismo , Astrocitos/virología , Moléculas de Adhesión Celular/metabolismo , Virus del Moquillo Canino/fisiología , Virus del Moquillo Canino/patogenicidad , Receptores de Superficie Celular/metabolismo , Sustitución de Aminoácidos , Animales , Antígenos CD/genética , Encéfalo/metabolismo , Encéfalo/virología , Moléculas de Adhesión Celular/genética , Células Cultivadas , Chlorocebus aethiops , Moquillo/metabolismo , Moquillo/transmisión , Moquillo/virología , Virus del Moquillo Canino/genética , Perros , Genes Virales , Interacciones Huésped-Patógeno , Humanos , Virus del Sarampión/patogenicidad , Nectinas , Receptores de Superficie Celular/genética , Receptores Virales/genética , Receptores Virales/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Miembro 1 de la Familia de Moléculas Señalizadoras de la Activación Linfocitaria , Panencefalitis Esclerosante Subaguda/etiología , Células Vero , Proteínas Virales/genética , Proteínas Virales/metabolismo , Internalización del VirusRESUMEN
Membrane fusion for morbillivirus cell entry relies on critical interactions between the viral fusion (F) and attachment (H) envelope glycoproteins. Through extensive mutagenesis of an F cavity recently proposed to contribute to F's interaction with the H protein, we identified two neighboring hydrophobic residues responsible for severe F-to-H binding and fusion-triggering deficiencies when they were mutated in combination. Since both residues reside on one side of the F cavity, the data suggest that H binds the F globular head domain sideways.
Asunto(s)
Virus del Moquillo Canino/fisiología , Multimerización de Proteína , Proteínas del Envoltorio Viral/metabolismo , Internalización del Virus , Animales , Análisis Mutacional de ADN , Virus del Moquillo Canino/genética , Modelos Moleculares , Unión Proteica , Conformación Proteica , Proteínas del Envoltorio Viral/genéticaRESUMEN
The hemagglutinin (H) gene of canine distemper virus (CDV) encodes the receptor-binding protein. This protein, together with the fusion (F) protein, is pivotal for infectivity since it contributes to the fusion of the viral envelope with the host cell membrane. Of the two receptors currently known for CDV (nectin-4 and the signaling lymphocyte activation molecule [SLAM]), SLAM is considered the most relevant for host susceptibility. To investigate how evolution might have impacted the host-CDV interaction, we examined the functional properties of a series of missense single nucleotide polymorphisms (SNPs) naturally accumulating within the H-gene sequences during the transition between two distinct but related strains. The two strains, a wild-type strain and a consensus strain, were part of a single continental outbreak in European wildlife and occurred in distinct geographical areas 2 years apart. The deduced amino acid sequence of the two H genes differed at 5 residues. A panel of mutants carrying all the combinations of the SNPs was obtained by site-directed mutagenesis. The selected mutant, wild type, and consensus H proteins were functionally evaluated according to their surface expression, SLAM binding, fusion protein interaction, and cell fusion efficiencies. The results highlight that the most detrimental functional effects are associated with specific sets of SNPs. Strikingly, an efficient compensational system driven by additional SNPs appears to come into play, virtually neutralizing the negative functional effects. This system seems to contribute to the maintenance of the tightly regulated function of the H-gene-encoded attachment protein. Importance: To investigate how evolution might have impacted the host-canine distemper virus (CDV) interaction, we examined the functional properties of naturally occurring single nucleotide polymorphisms (SNPs) in the hemagglutinin gene of two related but distinct strains of CDV. The hemagglutinin gene encodes the attachment protein, which is pivotal for infection. Our results show that few SNPs have a relevant detrimental impact and they generally appear in specific combinations (molecular signatures). These drastic negative changes are neutralized by compensatory mutations, which contribute to maintenance of an overall constant bioactivity of the attachment protein. This compensational mechanism might reflect the reaction of the CDV machinery to the changes occurring in the virus following antigenic variations critical for virulence.
Asunto(s)
Sustitución de Aminoácidos , Virus del Moquillo Canino/genética , Virus del Moquillo Canino/fisiología , Hemaglutininas Virales/genética , Hemaglutininas Virales/metabolismo , Mutación Missense , Acoplamiento Viral , Animales , Animales Salvajes , Antígenos CD/metabolismo , Análisis Mutacional de ADN , Moquillo/epidemiología , Moquillo/virología , Virus del Moquillo Canino/aislamiento & purificación , Europa (Continente)/epidemiología , Evolución Molecular , Mutagénesis Sitio-Dirigida , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Unión Proteica , Receptores de Superficie Celular/metabolismo , Receptores Virales/metabolismo , Miembro 1 de la Familia de Moléculas Señalizadoras de la Activación Linfocitaria , Supresión Genética , Proteínas Virales de Fusión/metabolismoRESUMEN
UNLABELLED: The morbillivirus cell entry machinery consists of a fusion (F) protein trimer that refolds to mediate membrane fusion following receptor-induced conformational changes in its binding partner, the tetrameric attachment (H) protein. To identify molecular determinants that control F refolding, we generated F chimeras between measles virus (MeV) and canine distemper virus (CDV). We located a central pocket in the globular head domain of CDV F that regulates the stability of the metastable, prefusion conformational state of the F trimer. Most mutations introduced into this "pocket'" appeared to mediate a destabilizing effect, a phenotype associated with enhanced membrane fusion activity. Strikingly, under specific triggering conditions (i.e., variation of receptor type and H protein origin), some F mutants also exhibited resistance to a potent morbillivirus entry inhibitor, which is known to block F triggering by enhancing the stability of prefusion F trimers. Our data reveal that the molecular nature of the F stimulus and the intrinsic stability of metastable prefusion F both regulate the efficiency of F refolding and escape from small-molecule refolding blockers. IMPORTANCE: With the aim to better characterize the thermodynamic basis of morbillivirus membrane fusion for cell entry and spread, we report here that the activation energy barrier of prefusion F trimers together with the molecular nature of the triggering "stimulus" (attachment protein and receptor types) define a "triggering range," which governs the initiation of the membrane fusion process. A central "pocket" microdomain in the globular F head contributes substantially to the regulation of the conformational stability of the prefusion complexes. The triggering range also defines the mechanism of viral escape from entry inhibitors and describes how the cellular environment can affect membrane fusion efficiency.