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

SERPINI1 serves as a biomarker promoting cell proliferation and invasion in hepatocellular carcinoma

BACKGROUND

SERPINI1 is a protein-coding gene, which has been reported to be related to malignancies, and the encoding protein is a secreted protein. Nevertheless, the specific effect of SERPINI1 on Hepatocellular carcinoma (HCC) remains unclear.

METHODS

The expression level of SERPINI1 in cancers was detected by the Gene Expression Omnibus (GEO) database, the Gene Expression Profiling Interactive Analysis (GEPIA) database and the collected serum of HCC patients. The receiver operating characteristic (ROC) curve and area under curve (AUC) were used to evaluate the diagnostic effectiveness of serum SERPINI1 and the combination of AFP and SERPINI1 for HCC. The Kaplan-Meier (KM) survival was used to evaluate the prognostic capacity of SERPINI1 for HCC in GEPIA database. Furthermore, the correlations between clinicopathological characteristics and the level of serum SERPINI1 were analyzed. Besides, we detected the expression of SERPINI1 in HepG2 by qPCR and western blot, and confirmed the biological function of SERPINI1 through MTT, EdU, wound healing and transwell invasion assay.

RESULTS

The results indicated that the level of SERPINI1 was significantly increased in tissue and serum of HCC patients. ROC analysis displayed that SERPINI1 had a significantly diagnostic value for HCC, the combination of AFP and SERPINI1 gained the higher specificity and sensitivity. The KM survival curves indicated that patients with SERPINI1 overexpression had worse overall survival. Furthermore, we found the positive correlations between serum SERPINI1 level and some clinicopathological characteristics, such as tumor size, differentiation degrees and so on. In addition, in vitro experiments revealed that SERPINI1 could promote the proliferation and invasion of HCC.

CONCLUSIONS

Taken together, our study demonstrates that SERPINI1, which is highly expressed in HCC and closely related to cell proliferation and invasion, may serve as a novel biomarker for diagnosis and prognosis of HCC.

Diagnostic and therapeutic value of human serpin family proteins

SERPIN (serine proteinase inhibitors) is an acronym for the superfamily of structurally similar proteins found in animals, plants, bacteria, viruses, and archaea. Over 1500 SERPINs are known in nature, while only 37 SERPINs are found in humans, which participate in inflammation, coagulation, angiogenesis, cell viability, and other pathophysiological processes. Both qualitative or quantitative deficiencies or overexpression and/or abnormal accumulation of SERPIN can lead to diseases commonly referred to as "serpinopathies". Hence, strategies involving SERPIN supplementation, elimination, or correction are utilized and/or under consideration. In this review, we discuss relationships between certain SERPINs and diseases as well as putative strategies for the clinical explorations of SERPINs.

Neuroserpin: structure, function, physiology and pathology

Neuroserpin is a serine protease inhibitor identified in a search for proteins implicated in neuronal axon growth and synapse formation. Since its discovery over 30 years ago, it has been the focus of active research. Many efforts have concentrated in elucidating its neuroprotective role in brain ischemic lesions, the structural bases of neuroserpin conformational change and the effects of neuroserpin polymers that underlie the neurodegenerative disease FENIB (familial encephalopathy with neuroserpin inclusion bodies), but the investigation of the physiological roles of neuroserpin has increased over the last years. In this review, we present an updated and critical revision of the current literature dealing with neuroserpin, covering all aspects of research including the expression and physiological roles of neuroserpin, both inside and outside the nervous system; its inhibitory and non-inhibitory mechanisms of action; the molecular structure of the monomeric and polymeric conformations of neuroserpin, including a detailed description of the polymerisation mechanism; and the involvement of neuroserpin in human disease, with particular emphasis on FENIB. Finally, we briefly discuss the identification by genome-wide screening of novel neuroserpin variants and their possible pathogenicity.

N-Glycosylation as a Tool to Study Antithrombin Secretion, Conformation, and Function

N-linked glycosylation is a crucial post-translational modification involved in protein folding, function, and clearance. N-linked glycosylation is also used therapeutically to enhance the half-lives of many proteins. Antithrombin, a serpin with four potential N-glycosylation sites, plays a pivotal role in hemostasis, wherein its deficiency significantly increases thrombotic risk. In this study, we used the introduction of N-glycosylation sites as a tool to explore what effect this glycosylation has on the protein folding, secretion, and function of this key anticoagulant. To accomplish this task, we introduced an additional N-glycosylation sequence in each strand. Interestingly, all regions that likely fold rapidly or were surrounded by lysines were not glycosylated even though an N-glycosylation sequon was present. The new sequon in the strands of the A- and B-sheets reduced secretion, and the B-sheet was more sensitive to these changes. However, the mutations in the strands of the C-sheet allowed correct folding and secretion, which resulted in functional variants. Therefore, our study revealed crucial regions for antithrombin secretion and could potentially apply to all serpins. These results could also help us understand the functional effects of natural variants causing type-I deficiencies.

Increased anxiety was found in serpini1 knockout zebrafish larval

Serpini1, which encodes neuroserpin, has been implicated in the development and normal function of the nervous system. Mutations in serpini1 cause familial encephalopathy, a rare neurodegenerative disorder characterized with neuroserpin inclusion bodies. However, function of neuroserpin in the nervous system is not fully understood. In this study, we generated a novel serpini1 mutant zebrafish model to investigate the loss of function of neuroserpin. Serpini1- deficient mutation was created with the CRISPR/Cas9 technique. No severe morphological characteristics were found in serpini1- deficient zebrafish. Serpini1-/- zebrafish larvae did not cause locomotor defects but displayed anxiety-like behavior. Extension of motoneurons axon defect was observed in serpini1-/- zebrafish. Furthermore, RNA-sequencing analysis revealed that loss of serpini1 resulted in affected expression of neurodegeneration-related genes.

Dynamic and structural insights into tick serpin from Ixodes ricinus

Ixodid ticks have a crucial impact on people and domestic animals worldwide. These parasites also pose a serious threat to livestock. To date, vaccination of hosts against ticks is a safer, more sustainable alternative to chemical control of ticks and the disease agents they transmit. Because of their roles in tick physiology, serpins (serine protease inhibitors) from tick saliva are among the candidates for anti-tick vaccines. Inhibitory serpins employ a suicide inhibition mechanism to inhibit proteases, where the serpin reactive centre loop (RCL) is cleaved, by the targeted protease, and then inserted into the main β-sheet of the serpin. This causes a massive conformational change called the 'stressed to relaxed' (S→R) transition, leading to the breakdown of serpin into two regions (core domain and cleaved polypeptide). Recently, the first tick serpin crystal structure from Ixodes ricinus in R-state was reported. We thus employed molecular dynamics simulations to better understand serpin structure and dynamics in atomic detail. Overall, R-state serpin showed high rigidity, especially the core domain. The most flexible region is the terminal of the cleaved polypeptide, due to its high-water exposure, while the rest of the cleaved polypeptide is stably trapped behind the core domain. T363, D367 and N375 are found to play a vital role in protein-protein attachment. This finding can be used to explain the high stability of the R-state serpin at the atomic level and provides insight into this tick serpin which will be useful for rational anti-tick vaccine development. AbbreviationsMDMolecular DynamicsRCLReactive centre loopCommunicated by Ramaswamy H. Sarma.

A hydrophobic patch surrounding Trp154 in human neuroserpin controls the helix F dynamics with implications in inhibition and aggregation

Neuroserpin (NS) mediated inhibition of tissue-type plasminogen activator (tPA) is important for brain development, synapse formation and memory. Aberrations in helix F and β-sheet A movement during inhibition can directly lead to epilepsy or dementia. Conserved W154 residue in a hydrophobic patch between helix F and β-sheet A is ideally placed to control their movement during inhibition. Molecular Dynamics (MD) simulation on wild type (WT) NS and its two variants (W154A and W154P) demonstrated partial deformation in helix F and conformational differences in strands 1A and 2A only in W154P. A fluorescence and Circular Dichroism (CD) analysis with purified W154 variants revealed a significant red-shift and an increase in α-helical content in W154P as compared to W154A and WT NS. Kinetics of tPA inhibition showed a decline in association rates (ka) for W154A as compared to WT NS with indication of complex formation. Appearance of cleaved without complex formation in W154P indicates that the variant acts as substrate due to conformational misfolding around helix F. Both the variants however showed increased rate of aggregation as compared to WT NS. The hydrophobic patch identified in this study may have importance in helix F dynamics of NS.