Amyloid-Associated Nucleic Acid Hybridisation

Nucleic acids promote amyloid formation in diseases including Alzheimer's and Creutzfeldt-Jakob disease. However, it remains unclear whether the close interactions between amyloid and nucleic acid allow nucleic acid secondary structure to play a role in modulating amyloid structure and function. Here we have used a simplified system of short basic peptides with alternating hydrophobic and hydrophilic amino acid residues to study nucleic acid - amyloid interactions. Employing biophysical techniques including X-ray fibre diffraction, circular dichroism spectroscopy and electron microscopy we show that the polymerized charges of nucleic acids concentrate and enhance the formation of amyloid from short basic peptides, many of which would not otherwise form fibres. In turn, the amyloid component binds nucleic acids and promotes their hybridisation at concentrations below their solution Kd, as shown by time-resolved FRET studies. The self-reinforcing interactions between peptides and nucleic acids lead to the formation of amyloid nucleic acid (ANA) fibres whose properties are distinct from their component polymers. In addition to their importance in disease and potential in engineering, ANA fibres formed from prebiotically-produced peptides and nucleic acids may have played a role in early evolution, constituting the first entities subject to Darwinian evolution

The regulation of phospholipase D by inositol phospholipids and small GTPases

AbstractPhospholipase D1 and D2 (PLD1, PLD2) both have PX and PH domains in their N-terminal regions with these inositol lipid binding domains playing key roles in regulating PLD activity and localisation. The activity of PLD1 is also regulated by protein kinase C and members of the Rho and Arf families of GTPases. Each of these proteins binds to unique sites; however, there appears to be little in vitro discrimination between individual family members. In agonist-stimulated cells, however, there is specificity, with, for example in RBL-2H3 cells, antigen stimulating the activation of PLD1 by association with Arf6, Rac1 and protein kinase Cα. PLD2 appears to be less directly regulated by GTPases and rather is primarily controlled through interaction with phosphatidylinositol 4-phosphate 5-kinase that generates the activating phosphatidylinositol 4,5-bisphosphate

Phospholipase D activity is essential for actin localization and actin-based motility in Dictyostelium

PLD (phospholipase D) activity catalyses the generation of the lipid messenger phosphatidic acid, which has been implicated in a number of cellular processes, particularly the regulation of membrane traffic. In the present study, we report that disruption of PLD signalling causes unexpectedly profound effects on the actin-based motility of Dictyostelium. Cells in which PLD activity is inhibited by butan-1-ol show a complete loss of actin-based structures, accompanied by relocalization of F-actin into small clusters, and eventually the nucleus, without a visible fall in levels of F-actin. Addition of exogenous phosphatidic acid reverses the effects of butan-1-ol, confirming that these effects are caused by inhibition of PLD. Loss of motility correlates with complete inhibition of endocytosis and a reduction in phagocytosis. Inhibition of PLD caused a major decrease in the synthesis of PtdIns(4,5)P(2), which could again be reversed by exogenously applied phosphatidic acid. Thus the essential role of PLD signalling in both motility and endocytosis appears to be mediated directly via regulation of PtdIns(4)P kinase activity. This implies that localized PLD-regulated synthesis of PtdIns(4,5)P(2) is essential for Dictyostelium actin function