Molecular bases of neuroserpin function and pathology

Abstract

Serpins build a large and evolutionary widespread protein superfamily, hosting members that are mainly Ser-protease inhibitors. Typically, serpins display a conserved core domain composed of three main β-sheets and 9-10 α-helices, for a total of approximately 350 amino acids. Neuroserpin (NS) is mostly expressed in neurons and in the central and peripheral nervous systems, where it targets tissue-type plasminogen activator. NS activity is relevant for axogenesis, synaptogenesis and synaptic plasticity. Five (single amino acid) NS mutations are associated with severe neurodegenerative disease in man, leading to early onset dementia, epilepsy and neuronal death. The functional aspects of NS protease inhibition are linked to the presence of a long exposed loop (reactive center loop, RCL) that acts as bait for the incoming partner protease. Large NS conformational changes, associated with the cleavage of the RCL, trap the protease in an acyl-enzyme complex. Contrary to other serpins, this complex has a half-life of approximately 10 min. Conformational flexibility is held to be at the bases of NS polymerization leading to Collins bodies intracellular deposition and neuronal damage in the pathological NS variants. Two main general mechanisms of serpin polymerization are currently discussed. Both models require the swapping of the RCL among neighboring serpin molecules. Specific differences in the size of swapped regions, as well as differences in the folding stage at which polymerization can occur, distinguish the two models. The results provided by recent crystallographic and biophysical studies allow rationalization of the functional and pathological roles played by NS based on the analysis of four three-dimensional structures.

The stability and activity of human neuroserpin are modulated by a salt bridge that stabilises the reactive centre loop

“…5a,b ). We clearly observed the rapid formation of the complex, and since the complex is known to be fragile at late stages 10 30 , we also observed the appearance of protein bands corresponding to cleaved NS and to non-complexed tPA, as well as the reduction in intensity of the complex. The densities of the gel bands in Fig.…”

Functional and dysfunctional conformers of human neuroserpin characterized by optical spectroscopies and Molecular Dynamics

“…Neuroserpin (NS) is an axonally secreted protein [1] , belonging to the Serpin family (SERine Protease INhibitor) [2] . NS is an inhibitor of tissue-type plasminogen activator, with a role in physiological processes [3] such as synaptic plasticity, memory, or sterol metabolism [4] , as well as in pathological contexts, such as Alzheimer disease [5] . 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 [7–10] .…”

The Tempered Polymerization of Human Neuroserpin

“…The protease cleaves the RCL triggering the insertion of the RCL into the A β-sheet as a strand; however, the protease remains covalently trapped, almost irreversibly, as an acyl enzyme intermediate [4]. The mechanism of serpin polymerization is intimately related to their inhibitory function [5], [6]. Indeed, unlike other globular proteins, native serpins are folded in a metastable conformation, and reach a more stable state by interlocking the RCL into the A β-sheet, thus reducing its mobility [7].…”

“…Here, we study the mechanism of polymerization of human neuroserpin (NS), a secretory protein produced mainly in neurons, playing a role in axonogenesis and in regulating synaptic plasticity through the inhibition of tissue-type plasminogen activator (tPA) [6], [12], [13]. It is also associated to Alzheimer's disease through a still not clear role [14], [15].…”