Fibril stability in solutions of twisted beta-sheet peptides: a new kind of micellization in chiral systems

The problem of fibril (fibre) formation in chiral systems is explored theor etically being supported by experiments on synthetic de novo 11-mer peptide forming self-assembled P-sheet tapes. Experimental data unambiguously indi cate that the tapes form fibrils of nearly monodisperse thickness ca. 8-10 nm. Fibril formation and stabilisation are attributed to inter-tape face-to -face attraction and their intrinsic twist, correspondingly The proposed th eory is capable of predicting the fibril aggregation number and its equilib rium twist in terms of molecular parameters of the primary tapes. The sugge sted novel mechanism of twist stabilisation of finite aggregates (fibrils) is different to the well-known stabilisation of micelles in amphiphilic sys tems, and it is: likely to explain the formation and stability of fibrils i n a wide variety of systems including proteinaceous amyloid fibres, sickle- cell hemoglobin fibres responsible for HbS anemia, corkscrew threads found in chromonics in the presence of chiral additives and native cellulose micr ofibrillar crystallites. The theory also makes it possible to extract the b asic molecular parameters of primary tapes (inter-tape attraction energy, h elical twist step, elastic moduli) from the experimental data.