NMR study of mutations of glycine-52 of the catalytic domain of diphtheria toxin

Cross-reacting-material 197 (CRM197) is a naturally occurring non-toxic mutant of diphtheria toxin (DT) that is one of the few carrier protein used in the manufacture of polysaccharide vaccines targeting bacterial pathogens such as Neisseria meningitidis, Streptococcus pneumaniae and Haemophilus influenzae. A detailed explanation in structural terms for the lack of toxicity has started to emerge with the report of the X-ray structure of CRM197. Here, we present an NMR spectroscopy study of the wild-type catalytic domain of diphtheria toxin and the effects of mutations at residue 52 on its conformation. We utilized a strategy that consisted of gradually inducing steric perturbations by increasing the side chain size of the residue. Results show that the catalytic domain does not tolerate even the smallest perturbation, such as a glycine to alanine substitution, resulting in the destabilization of domain fold leading to protein aggregation. The observed behavior is further exacerbated with the substitution of amino acids with larger side chains. These findings support the concept that the lack of toxicity observed for CRM197 is the result of a highly unstable conformation of its catalytic domain that, upon insertion into the cell, cannot properly refold and perform its catalytic activity responsible for the arrest of all cellular protein synthesis

Assessment of the higher order structure of Humira® Remicade® Avastin® Rituxan® Herceptin® and Enbrel® by 2D-NMR fingerprinting

The advent of monoclonal antibody biosimilar products has stimulated the development of analytical methods that can better characterize an important quality attribute, namely the higher order structure (HOS). Here, we propose a simple approach based on heteronuclear 2D NMR techniques at natural abundance for generating spectral fingerprints of the HOS at high resolution. We show that the proposed method can assess the HOS of six therapeutic products, adalimumab (Humira®), bevacizumab (Avastin®), infliximab (Remicade®), rituximab (Rituxan®), trastuzumab (Herceptin®), and Etanercept (Enbrel®). After treatment with immobilized papain, the purified fragments (Fab and Fc) were analyzed by 2D proton-nitrogen and proton-carbon NMR correlations. All Fab and Fc fragments produced high-resolution 2D-NMR spectra from which assessment of their higher order structure can be performed in the context of comparability studies. In particular, the two different sequences of Fc fragments could be unambiguously distinguished. The results show that it is possible to obtain structurally dependent information at amino acid resolution of these important therapeutic agents

Neuronal Fiber--tracking via optimal mass transportation

Diffusion Magnetic Resonance Imaging (MRI) is used to (non-invasively) study neuronal fibers in the brain white matter. Reconstructing fiber paths from such data (tractography problem) is relevant in particular to study the connectivity between two given cerebral regions. By considering the fiber paths between two given areas as geodesics of a suitable well-posed optimal control problem (related to optimal mass transportation) which takes into account the whole information given by the DDF, we are able to provide a quantitative criterion to estimate the connectivity between two given cerebral regions, and to recover the actual distribution of neuronal fibers between them

Topoisomerase 1 suppresses replication stress and genomic instability by preventing interference between replication and transcription.

International audienceTopoisomerase I (Top1) is a key enzyme acting at the interface between DNA replication, transcription and mRNA maturation. Here, we show that Top1 suppresses genomic instability in mammalian cells by preventing conflicts between transcription and DNA replication. Using DNA combing and ChIP-on-chip, we found that Top1-deficient cells accumulate stalled replication forks and chromosome breaks in S phase and that breaks occur preferentially at gene-rich regions of the genome. Strikingly, these phenotypes were suppressed by preventing the formation of RNA-DNA hybrids (R-loops) during transcription. Moreover, these defects could be mimicked by depletion of the splicing factor ASF/SF2, which interacts functionally with Top1. Taken together, these data indicate that Top1 prevents replication fork collapse by suppressing the formation of R-loops in an ASF/SF2-dependent manner. We propose that interference between replication and transcription represents a major source of spontaneous replication stress, which could drive genomic instability during early stages of tumorigenesis