The N-Terminus of GalE Induces tmRNA Activity in Escherichia coli

BACKGROUND: The tmRNA quality control system recognizes stalled translation complexes and facilitates ribosome recycling in a process termed 'ribosome rescue'. During ribosome rescue, nascent chains are tagged with the tmRNA-encoded SsrA peptide, which targets tagged proteins for degradation. In Escherichia coli, tmRNA rescues ribosomes arrested on truncated messages, as well as ribosomes that are paused during elongation and termination. METHODOLOGY/PRINCIPAL FINDINGS: Here, we describe a new translational pausing determinant that leads to SsrA peptide tagging of the E. coli GalE protein (UDP-galactose 4-epimerase). GalE chains are tagged at more than 150 sites, primarily within distinct clusters throughout the C-terminal domain. These tagging sites do not correspond to rare codon clusters and synonymous recoding of the galE gene had little effect on tagging. Moreover, tagging was largely unaffected by perturbations that either stabilize or destabilize the galE transcript. Examination of GalE-thioredoxin (TrxA) fusion proteins showed that the GalE C-terminal domain is no longer tagged when fused to an N-terminal TrxA domain. Conversely, the N-terminus of GalE induced tagging within the fused C-terminal TrxA domain. CONCLUSIONS/SIGNIFICANCE: These findings suggest that translation of the GalE N-terminus induces subsequent tagging of the C-terminal domain. We propose that co-translational maturation of the GalE N-terminal domain influences ribosome pausing and subsequent tmRNA activity

MOG cell-based assay detects non-MS patients with inflammatory neurologic disease

Objective: To optimize sensitivity and disease specificity of a myelin oligodendrocyte glycoprotein (MOG) antibody assay. Methods: Consecutive sera (n 5 1,109) sent for aquaporin-4 (AQP4) antibody testing were screened for MOG antibodies (Abs) by cell-based assays using either full-length human MOG (FL-MOG) or the short-length form (SL-MOG). The Abs were initially detected by Alexa Fluor goat anti-human IgG (H 1 L) and subsequently by Alexa Fluor mouse antibodies to human IgG1. Results: When tested at 1:20 dilution, 40/1,109 sera were positive for AQP4-Abs, 21 for SLMOG, and 180 for FL-MOG. Only one of the 40 AQP4-Ab–positive sera was positive for SLMOG-Abs, but 10 (25%) were positive for FL-MOG-Abs (p 5 0.0069). Of equal concern, 48% (42/88) of sera from controls (patients with epilepsy) were positive by FL-MOG assay. However, using an IgG1-specific secondary antibody, only 65/1,109 (5.8%) sera were positive on FL-MOG, and AQP4-Ab– positive and control sera were negative. IgM reactivity accounted for the remaining anti-human IgG (H 1 L) positivity toward FL-MOG. The clinical diagnoses were obtained in 33 FL-MOG–positive patients, blinded to the antibody data. IgG1-Abs to FL-MOG were associated with optic neuritis (n 5 11), AQP4-seronegative neuromyelitis optica spectrum disorder (n 5 4), and acute disseminated encephalomyelitis (n 5 1). All 7 patients with probable multiple sclerosis (MS) were MOG-IgG1 negative. Conclusions: The limited disease specificity of FL-MOG-Abs identified using Alexa Fluor goat antihuman IgG (H 1 L) is due in part to detection of IgM-Abs. Use of the FL-MOG and restricting to IgG1-Abs substantially improves specificity for non-MS demyelinating diseases. Classification of evidence: This study provides Class II evidence that the presence of serum IgG1- MOG-Abs in AQP4-Ab–negative patients distinguishes non-MS CNS demyelinating disorders from MS (sensitivity 24%, 95% confidence interval [CI] 9%–45%; specificity 100%, 95% CI 88%–100%)

MOG cell-based assay detects non-MS patients with inflammatory neurologic disease

Objective: To optimize sensitivity and disease specificity of a myelin oligodendrocyte glycoprotein (MOG) antibody assay. Methods: Consecutive sera (n 5 1,109) sent for aquaporin-4 (AQP4) antibody testing were screened for MOG antibodies (Abs) by cell-based assays using either full-length human MOG (FL-MOG) or the short-length form (SL-MOG). The Abs were initially detected by Alexa Fluor goat anti-human IgG (H 1 L) and subsequently by Alexa Fluor mouse antibodies to human IgG1. Results: When tested at 1:20 dilution, 40/1,109 sera were positive for AQP4-Abs, 21 for SLMOG, and 180 for FL-MOG. Only one of the 40 AQP4-Ab–positive sera was positive for SLMOG-Abs, but 10 (25%) were positive for FL-MOG-Abs (p 5 0.0069). Of equal concern, 48% (42/88) of sera from controls (patients with epilepsy) were positive by FL-MOG assay. However, using an IgG1-specific secondary antibody, only 65/1,109 (5.8%) sera were positive on FL-MOG, and AQP4-Ab– positive and control sera were negative. IgM reactivity accounted for the remaining anti-human IgG (H 1 L) positivity toward FL-MOG. The clinical diagnoses were obtained in 33 FL-MOG–positive patients, blinded to the antibody data. IgG1-Abs to FL-MOG were associated with optic neuritis (n 5 11), AQP4-seronegative neuromyelitis optica spectrum disorder (n 5 4), and acute disseminated encephalomyelitis (n 5 1). All 7 patients with probable multiple sclerosis (MS) were MOG-IgG1 negative. Conclusions: The limited disease specificity of FL-MOG-Abs identified using Alexa Fluor goat antihuman IgG (H 1 L) is due in part to detection of IgM-Abs. Use of the FL-MOG and restricting to IgG1-Abs substantially improves specificity for non-MS demyelinating diseases. Classification of evidence: This study provides Class II evidence that the presence of serum IgG1- MOG-Abs in AQP4-Ab–negative patients distinguishes non-MS CNS demyelinating disorders from MS (sensitivity 24%, 95% confidence interval [CI] 9%–45%; specificity 100%, 95% CI 88%–100%)