Spectroscopic evidence of tetanus toxin translocation domain bilayer-induced refolding and insertion

Pervasive, conserved secondary structure in highly charged protein regions

Understanding how protein sequences confer function remains a defining challenge in molecular biology. Two approaches have yielded enormous insight yet are often pursued separately: structure-based, where sequence-encoded structures mediate function, and disorder-based, where sequences dictate physicochemical and dynamical properties which determine function in the absence of stable structure. Here we study highly charged protein regions (>40% charged residues), which are routinely presumed to be disordered. Using recent advances in structure prediction and experimental structures, we show that roughly 40% of these regions form well-structured helices. Features often used to predict disorder-high charge density, low hydrophobicity, low sequence complexity, and evolutionarily varying length-are also compatible with solvated, variable-length helices. We show that a simple composition classifier predicts the existence of structure far better than well-established heuristics based on charge and hydropathy. We show that helical structure is more prevalent than previously appreciated in highly charged regions of diverse proteomes and characterize the conservation of highly charged regions. Our results underscore the importance of integrating, rather than choosing between, structure- and disorder-based approaches.

Comparative Analysis of Antigenic Strength and In vivo Serum Antibodies Concentration of Tetanus Toxoid Vaccine Adsorbed in Pakistan

Clostridium tetani produce tetanospasmin, a potent exotoxin; that causes tetanus or lockjaw disease. Scientists developed an anti-tetanus toxoid to protect the body from the spasm's neurotoxic effect. In Pakistan recently, 478 cases of neonatal tetanus were reported. The study was carried out at The National Control Laboratory for Biologicals Islamabad, aiming to decipher the effectiveness of the most frequently used tetanus toxoid vaccine adsorbed in Pakistan in comparison to standard reference vaccine having earlier known consistent values. The vaccines included domestic public sector, domestic private sector, imported private sector I, and imported private sector II. The triplicate experiments on purebred Swiss albino mice were performed by immunizing with Tetanus toxoid and then tested parallel with standard reference vaccine. Various analytical tests were performed on the test organism that included flocculation test/identity test, antibody quantification using enzyme-linked immunosorbent assay (ELISA), potency test, abnormal toxicity test, osmolality, pH test, liquid sub-visible particle test, and sterility test. Results of all the vaccines were compared in comparison with the standard reference vaccine. Absorbances of test vaccines were recorded at the lowest dilution by ELISA. The domestic private sector, imported private sector I, imported private sector II and standard reference vaccine were flocculated at mean dilution (Mean: 0.24, 95% CI: 0.1903–0.2897), and the domestic public sector was flocculated at mean dilution (Mean: 0.23, 95% CI: 0.2052–0.2548). All the products were found within the normal ranges where it was concluded that the maximum average titer of 2.81 was observed at dilution 10^−1.6, indicating that these vaccines were adequate/suitable for the prevention of tetanus.

Advantages of Quantitative Analysis of Depth-Dependent Fluorescence Quenching: Case Study of BAX

Dynamic disorder of the lipid bilayer presents a challenge for establishing structure-function relationships in membrane proteins, especially to those that insert by refolding from soluble states, e.g., bacterial toxins and Bcl-2 apoptotic regulators. Because many high-resolution structural techniques cannot be easily applied to such systems, methods like depth-dependent fluorescence quenching gained prominence. Over three decades ago, Prof. Erwin London and his co-workers revolutionized the studies of membrane protein insertion by introducing a quantitative approach to the analysis of membrane quenching data and inspired many researchers to continue this work. Here, we illustrate how the application of the quantitative analysis yields new insights into previously published results. We have used the method of distribution analysis (DA) to calculate the precise immersion depth of NBD fluorophores selectively attached to various single-cysteine mutants of the apoptotic factor BAX from quenching data obtained with a series of spin-labeled lipids. The original qualitative analysis interpreted the higher quenching determined for shallower probes in positions flanking the helix 9 of BAX as evidence of a transmembrane helix 9 topology. The quantitative DA, however, revealed that a transmembrane topology of helix 9 of BAX is unlikely, as it would require labeling sites that are only 15 residues apart in a helical conformation to be separated by a transverse distance of over 45 Å.