Early events in disease associated protein misfolding

Sammanfattning: The scope of this thesis is to unravel some of the mysteries concerning events takingplace early in the amyloid cascade. In vitro studies of early misfolded states ofamyloidogenic proteins are important since the use of recombinant proteins allow us to monitor slight changes in environmental conditions as well as in amino acid composition and thereby illuminate the problem at near atomic resolution.Human prion protein (HuPrP) (associated with e.g. Creutzfeldt-Jakob disease) andthe Aβ1-42 peptide (associated with Alzheimer’s disease) recombinantly expressed in Escherichia coli have been used as model systems for these studies.A new protocol for amyloid fibril formation of human prion protein under native conditions was developed. This revealed an unusual pathway of conformational conversion from early formed disordered aggregates that later matured into amyloidfibrils.The polymorphism 129M/V in HuPrP has a large impact on susceptibility both to sporadic and infectious prion diseases. Some features of this polymorphism havebeen elucidated, employing a mutational study in position 129 (M, A, L, V, P, M, W,E, and K). These investigations have rendered new knowledge about the impact ofsize, charge and β-carbon branching in position 129 upon early intermolecular interactions and the effects of fibril seeding.Investigations of the interactions between different assembly forms of HuPrP and components of the innate immune system revealed that both native, oligomeric and fibrillar forms of HuPrP activate both the classical and alternative pathways of the Complement System. Most efficient activation is achieved upon binding of oligomeric HuPrP to the complement component C1q.We have developed a system for recombinant expression of human A,1-42. The monomeric peptides are assembled into various sized soluble oligomers (trimer, hexamer, nonamer, dodecamer). The oligomeric forms were stable in 8 M urea, 6 MGuHCl and SDS suggesting that these were covalently cross-linked. Some mechanistic features in the assembly process have been investigated and we have shown that cupric ions facilitates formation of stable oligomers in our system.