title: Two latent and two hyperstable polymeric forms of human neuroserpin.
abstract: Human neuroserpin (hNS) is a serine protease inhibitor that belongs to the serpin superfamily and is expressed in nervous tissues. The serpin fold is generally characterized by a long exposed loop, termed the reactive center loop, that acts as bait for the target protease. Intramolecular insertion of the reactive center loop into the main serpin β-sheet leads to the serpin latent form. As with other known serpins, hNS pathological mutants have been shown to accumulate as polymers composed of quasi-native protein molecules. Although hNS polymerization has been intensely studied, a general agreement about serpin polymer organization is still lacking. Here we report a biophysical characterization of native hNS that is shown to undergo two distinct conformational transitions, at 55°C and 85°C, both leading to distinct latent and polymeric species. The latent and polymer hNS forms obtained at 45°C and 85°C differ in their chemical and thermal stabilities; furthermore, the hNS polymers also differ in size and morphology. Finally, the 85°C polymer shows a higher content of intermolecular β-sheet interactions than the 45°C polymer. Together, these results suggest a more complex conformational scenario than was previously envisioned, and, in a general context, may help reconcile the current contrasting views on serpin polymerization.
authors.affiliation: Dipartimento di Scienze Biomolecolari e Biotecnologie, Università di Milano, Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Ricagno
authors.forename: Margherita
authors.initials: M
authors.lastname: Pezzullo
authors.forename: Alberto
authors.initials: A
authors.lastname: Barbiroli
authors.forename: Mauro
authors.initials: M
authors.lastname: Manno
authors.forename: Matteo
authors.initials: M
authors.lastname: Levantino
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Santangelo
authors.forename: Francesco
authors.initials: F
authors.lastname: Bonomi
authors.forename: Martino
authors.initials: M
authors.lastname: Bolognesi
mesh_terms: D002942:Circular Dichroism; D006801:Humans; D008027:Light; D009479:Neuropeptides / Q000737:chemistry / Q000378:metabolism*; D058105:Polymerization; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D055550:Protein Stability; D017433:Protein Structure, Secondary; D058767:Protein Unfolding; D012542:Scattering, Radiation; D015843:Serpins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D000097522:Neuroserpin
chemical_list: D009479:Neuropeptides; D020033:Protein Isoforms; D015843:Serpins; D000097522:Neuroserpin