Membrane interaction and disulphide-bridge formation in the unconventional secretion of Tau

Misfolded, pathological Tau protein propagates from cell to cell causing neuronal degeneration in Alzheimer’s disease and other tauopathies. The molecular mechanisms of this process have remained elusive. Unconventional secretion of Tau takes place via several different routes, including direct penetration through the plasma membrane. Here, we show that Tau secretion requires membrane interaction via disulphide bridge formation. Mutating residues that reduce Tau interaction with membranes or formation of disulphide bridges decrease both Tau secretion from cells, and penetration through artificial lipid membranes. Our results demonstrate that Tau is indeed able to penetrate protein-free membranes in a process independent of active cellular processes and that both membrane interaction and disulphide bridge formation are needed for this process. QUARK-based de novo modelling of the second and third microtubule-binding repeat domains, in which the two cysteine residues of 4R isoforms of Tau are located, supports the concept that this region of Tau could form transient amphipathic helices for membrane interaction.

Crystallography of lamin A facilitated by chimeric fusions

All proteins of the intermediate filament (IF) family contain the signature central α-helical domain which forms a coiled-coil dimer. Because of its length, past structural studies relied on a ‘divide-and-conquer’ strategy whereby fragments of this domain were recombinantly produced, crystallized and analysed using X-rays. Here we describe a further development of this approach towards structural studies of nuclear IF protein lamin. To this end, we have fused lamin A fragments to short N- and C-terminal capping motifs which provide for the correct formation of parallel, in-register coiled-coil dimers. As the result, a chimeric construct containing lamin A residues 17-70 C-terminally capped by the Eb1 domain was solved to 1.83 Å resolution. Another chimera containing lamin A residues 327-403 N-terminally capped by the Gp7 domain was solved to 2.9 Å. In the latter case the capping motif was additionally modified to include a disulphide bridge at the dimer interface. We discuss multiple benefits of fusing coiled-coil dimers with such capping motifs, including a convenient crystallographic phasing by either molecular replacement or sulphur single-wavelength anomalous dispersion (S-SAD) measurements.

Human Oral Defensins Antimicrobial Peptides: A Future Promising Antimicrobial Drug

The nature and structural composition of antimicrobial peptides are derived from their innate immune response and they are active against various bacteria, fungi and other microorganisms. The aim of this paper was to pool up the literature on the features of human oral defensins antimicrobial peptides. The defensins showed antimicrobial activity against Gram-positive and Gram-negative bacteria and various fungi and viruses. As with their other properties like antiviral, antifungal and antibacterial, human defensins peptides are thought to have a unique amino acid-based structure with Disulphide Bridge which makes them synthesize chemically or naturally with the help of these bacteria. The data contributing in this study was gathered from the research papers published in English language in the last twenty-five years. This literature mainly elaborates the general and analytical characteristics of antimicrobial peptides in the human oral cavity; focusing on the types, biochemistry, and mechanism of action of defensins with its clinical importance.

60 YEARS OF POMC: Purification and biological characterisation of melanotrophins and corticotrophins

The remarkable conservation of the primary structures and anatomical location of dogfish α-melanocyte-stimulating hormone (MSH), corticotrophin-like intermediate lobe peptide (CLIP) and adrenocorticotrophic hormone (ACTH) compared with mammals reinforced the tissue-specific processing hypothesis of ACTH peptides in the pituitary gland. The cloning of dogfish pro-opiomelanocortin (POMC) led to the identification of δ-MSH and simultaneously revealed the high conservation of the γ-MSH sequence during evolution. These studies have also shown that β-MSH is much less conserved during evolution and in some species is not even processed from β-LPH. Human pro-γ-MSH potentiates the corticosteroidogenic activity of ACTH and peptides generated from its N-terminal, in particular big-γ-MSH, appear to have adrenal mitogenic activity. Human big-γ-MSH (from the zona intermedia) may also cause the adrenache. The review finishes with a cautionary note with regard to the misdiagnosis of the ectopic ACTH syndrome in which partial processing of ACTH can result in large concentrations of α-MSH and CLIP, which can interfere in the performance of two-site immunoassays, and the problem of the correct disulphide bridge arrangement in synthetic N-POMC peptides is also discussed.

The malaria parasite egress protease SUB1 is a calcium-dependent redox switch subtilisin

Malaria is caused by a protozoan parasite that replicates within an intraerythrocytic parasitophorous vacuole. Release (egress) of malaria merozoites from the host erythrocyte is a highly regulated and calcium-dependent event that is critical for disease progression. Minutes before egress, an essential parasite serine protease called SUB1 is discharged into the parasitophorous vacuole, where it proteolytically processes a subset of parasite proteins that play indispensable roles in egress and invasion. Here we report the first crystallographic structure of Plasmodium falciparum SUB1 at 2.25 Å, in complex with its cognate prodomain. The structure highlights the basis of the calcium dependence of SUB1, as well as its unusual requirement for interactions with substrate residues on both prime and non-prime sides of the scissile bond. Importantly, the structure also reveals the presence of a solvent-exposed redox-sensitive disulphide bridge, unique among the subtilisin family, that likely acts as a regulator of protease activity in the parasite.

High-throughput production of two disulphide-bridge toxins

A quick and efficient production method compatible with high-throughput screening was developed using 36 toxins belonging to four different families of two disulphide-bridge toxins. Final toxins were characterized using HPLC co-elution, CD and pharmacology studies.