Anti-JC virus antibodies: implications for PML risk stratification.

OBJECTIVE: A study was undertaken to establish an enzyme-linked immunosorbent assay (ELISA) to detect JC virus (JCV)-specific antibodies in multiple sclerosis (MS) patients, and to evaluate its potential utility for identifying patients at higher or lower risk (ie, risk stratification) of developing progressive multifocal leukoencephalopathy (PML). METHODS: A 2-step assay for detecting and confirming the presence of anti-JCV antibodies in human serum and plasma was developed and demonstrated to be both sensitive and specific. ELISA cutpoints were statistically established using sera from >800 MS patients from natalizumab clinical studies. Subsequently, this assay was used to determine the presence of anti-JCV antibodies in natalizumab-treated PML patients where serum samples were collected 16-180 months prior to the diagnosis of PML. RESULTS: In our evaluation of natalizumab-treated MS patients, 53.6% tested positive for anti-JCV antibodies, with a 95% confidence interval of 49.9 to 57.3%. The false-negative rate of the ELISA was calculated to be approximately 2.5%, with an upper 1-sided confidence limit of 4.4%. Notably, we observed anti-JCV antibodies in all 17 available pre-PML sera samples, which was significantly different from the 53.6% seropositivity observed in the overall MS study population (p < 0.0001). INTERPRETATION: This 2-step assay provides a means to classify MS patients as having detectable or not detectable levels of anti-JCV antibodies. The finding that all 17 of the pre-PML samples that were available tested seropositive, and none tested seronegative, warrants further research on the clinical utility of the anti-JCV antibody assay as a potential tool for stratifying MS patients for higher or lower risk of developing PML.

Structural insights into the mechanism of the PLP synthase holoenzyme from Thermotoga maritima.

Pyridoxal 5'-phosphate (PLP) is the biologically active form of vitamin B6 and is an important cofactor for several of the enzymes involved in the metabolism of amine-containing natural products such as amino acids and amino sugars. The PLP synthase holoenzyme consists of two subunits: YaaD catalyzes the condensation of ribulose 5-phosphate, glyceraldehyde-3-phosphate, and ammonia, and YaaE catalyzes the production of ammonia from glutamine. Here we describe the structure of the PLP synthase complex (YaaD-YaaE) from Thermotoga maritima at 2.9 A resolution. This complex consists of a core of 12 YaaD monomers with 12 noninteracting YaaE monomers attached to the core. Compared with the previously published structure of PdxS (a YaaD ortholog in Geobacillus stearothermophilus), the N-terminus (1-18), which includes helix alpha0, the beta2-alpha2 loop (46-56), which includes new helix alpha2a, and the C-terminus (270-280) of YaaD are ordered in the complex but disordered in PdxS. A ribulose 5-phosphate is bound to YaaD via an imine with Lys82. Previous studies have demonstrated a similar imine at Lys149 and not at Lys81 (equivalent to Lys150 and Lys82 in T. maritima) for the Bacillus subtilis enzyme suggesting the possibility that two separate sites on YaaD are involved in PLP formation. A phosphate from the crystallization solution is found bound to YaaD and also serves as a marker for a possible second active site. An ammonia channel that connects the active site of YaaE with the ribulose 5-phosphate binding site was identified. This channel is similar to one found in imidazole glycerol phosphate synthase; however, when the beta-barrels of the two complexes are superimposed, the glutaminase domains are rotated by about 180 degrees with respect to each other.