Abstract
Neuroserpin (NS) is a serine protease inhibitor (SERPIN) involved in different neurological pathologies, including the Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB), related to the aberrant polymerization of NS mutants. Here we present an in vitro and in silico characterization of native neuroserpin and its dysfunctional conformation isoforms: the proteolytically cleaved conformer, the inactive latent conformer, and the polymeric species. Based on circular dichroism and fluorescence spectroscopy, we present an experimental validation of the latent model and highlight the main structural features of the different conformers. In particular, emission spectra of aromatic residues yield distinct conformational fingerprints, that provide a novel and simple spectroscopic tool for selecting serpin conformers in vitro. Based on the structural relationship between cleaved and latent serpins, we propose a structural model for latent NS, for which an experimental crystallographic structure is lacking. Molecular Dynamics simulations suggest that NS conformational stability and flexibility arise from a spatial distribution of intramolecular salt-bridges and hydrogen bonds.
Highlights
Neuroserpin (NS) is an axonally secreted protein [1], belonging to the Serpin family (SERine Protease INhibitor) [2]
Native NS, as other serpins, is natively folded in a metastable state that may convert into other conformational isoforms [16], namely the cleaved NS, resulting from protease cleavage during NS inhibitory activity, and the latent NS, a dysfunctional conformation inactive for inhibition, typically obtained by reactive central loop (RCL) insertion into the main NS A β-sheet without cleavage
We used Molecular Dynamics and optical spectroscopies to characterize in silico and in vitro the different NS conformers and to assess their structural and dynamical properties, as well as their freeenergies
Summary
Neuroserpin (NS) is an axonally secreted protein [1], belonging to the Serpin family (SERine Protease INhibitor) [2]. Site mutations in NS amino acid sequence cause an autosomal dominant dementia, known as Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB) [6], related to aberrant deposition of NS polymers [7,8,9,10]. Such pathology, characterized by an evident genotype–phenotype correlation [11], is a striking example of a class of conformational diseases, the serpinopathies, related to specific serpin site mutations, as in the case of the most common α1antitrypsin deficiency [12].
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