Scanning tunnelling microscopy analysis of octameric o-phenylenes on Au(111)

STM microscopy allowed direct observation of perfectly- and partially-folded conformers of OP8Br and OP8NO2on Au(111). The metastable partially-folded conformation was stabilized by their more efficient electronic coupling with the Au substrate.

A Partially Structured Species of β2-Microglobulin Is Significantly Populated under Physiological Conditions and Involved in Fibrillogenesis

The folding of β2-microglobulin (β2-m), the protein forming amyloid deposits in dialysis-related amyloidosis, involves formation of a partially folded conformation named I2, which slowly converts into the native fold, N. Here we show that the partially folded species I2can be separated from N by capillary electrophoresis. Data obtained with this technique and analysis of kinetic data obtained with intrinsic fluorescence indicate that the I2conformation is populated to ∼14 ± 8% at equilibrium under conditions of pH and temperature close to physiological. In the presence of fibrils extracted from patients, the I2conformer has a 5-fold higher propensity to aggregate than N, as indicated by the thioflavine T test and light scattering measurements. A mechanism of aggregation of β2-min vivoinvolving the association of the preformed fibrils with the fraction of I2existing at equilibrium is proposed from these results. The possibility of isolating and quantifying a partially folded conformer of β2-m involved in the amyloidogenesis process provides new opportunities to monitor hemodialytic procedures aimed at the reduction of such species from the pool of circulating β2-m but also to design new pharmaceutical approaches that consider such species as a putative molecular target.

Biogenesis of Tom40, Core Component of the Tom Complex of Mitochondria

Tom40 is an essential component of the preprotein translocase of the mitochondrial outer membrane (TOM complex) in which it constitutes the core element of the protein conducting pore. We have investigated the biogenesis of Tom40. Tom40 is inserted into the outer membrane by the TOM complex. Initially, Tom40 is bound as a monomer at the mitochondrial surface. The import receptor Tom20 is involved in this initial step; it stimulates both binding and efficient insertion of the Tom40 precursor. This step is followed by the formation of a further intermediate at which the Tom40 precursor is partially inserted into the outer membrane. Finally, Tom40 is integrated into preexisting TOM complexes. Efficient import appears to require the Tom40 precursor to be in a partially folded conformation. Neither the NH2 nor the COOH termini are necessary to target Tom40 to the outer membrane. However, the NH2-terminal segment is required for Tom40 to become assembled into the TOM complex. A model for the biogenesis of Tom40 is presented.