The necessary chances of a thermodynamically metastable protein: inactivation and polymeritzation of human neuroserpin

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Serpins are a wide class of proteins with high structural similarity, characterized by a unique substrate-like inhibitory mechanism that resembles a "molecular mousetrap". The active serpin is characterized by a main 5-stranded β-sheet and an exposed Reactive Centre Loop, which acts as abait for the target protease. The cleavage of the loop by the protease triggers the insertion of theloop into the β-sheet as a strand and the disruptive translocation of the protease. This peculiarconformational mobility is achievable since serpins fold into a metastable native conformation. Thisfeature gives a selective advantage to the serpin family to develop inhibitory activities, but leaves theseproteins labile to misfolding and dysfunctional mutations, which cause a class of diseases known asserpinopathies. Indeed, the thermodynamically stable non-functional conformation can be reachedwithout cleavage by intramolecular loop insertion (latent state) or by intermolecular insertion, leadingto polymerization.Neuroserpin is a an inhibitor of tissue-type plasminogen activator that has a role in manypathologies, such as ischemia, Alzheimer disease, and FENIB (Familial Encephalopathy withNeuroserpin Inclusion Body). It is particularly suited to study the molecular basis of serpin inactivationand polymerization, since it may form latent conformers and polymers by thermal activation even inthe wild type form.Here, we study the mechanism of neuroserpin unfolding and polymerization by differentexperimental techniques (static and dynamic light scattering, liquid chromatography, Fourier transforminfrared spectroscopy) and by the support of Molecular Dynamics simulations. Our results show thatat intermediate temperatures (45-55 °C) neuroserpin forms flexible polymers with a size from a fewtens to a few hundreds of nanometers. At high temperatures, above 80 °C, our results reveal adifferent polymeric form, reached through an analogous loop-sheet mechanism, with considerablylarger size and higher chemical stability. These observations highlight the fact that serpin polymerizationis context-dependent, and that polymers accumulated in serpinopathies under physiological conditionsmay be different for different serpin and even for different pathological mutants of the same serpin.
Lingua originaleEnglish
Numero di pagine0
Stato di pubblicazionePublished - 2009


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