Application of a dried blood spot based proteomic and genetic assay for diagnosing hereditary angioedema.

BACKGROUND: Hereditary angioedema (HAE) with C1-inhibitor deficiency (C1-INH-HAE) is a rare disease caused by low level (type I) or dysfunction (type II) of the C1-inhibitor protein with subsequent reduction of certain complement protein levels. METHODS: To develop and test the reliability of a two-tier method based on C1-INH and C4 quantitation followed by genetic analysis from dried blood spot (DBS) for establishing the diagnosis of C1-INH-HAE. C1-INH and C4 proteins have been quantified in human plasma using a classical immuno-assay and in DBS using a newly developed proteolytic liquid chromatography-mass spectrometry method. Genetic analysis was carried out as reported previously (PMID: 35386643) and by a targeted next-generation sequencing panel, multiplex ligation-dependent probe amplification and in some cases whole genome sequencing. RESULTS: DBS quantification of C1-INH and C4 showed the same pattern as plasma, offering the possibility of screening patients with AE symptoms either locally or remotely. Genetic analysis from DBS verified each of the previously identified SERPING1 mutations of the tested C1-INH-HAE patients and revealed the presence of other rare variations in genes that may be involved in the pathogenesis of AE episodes. CONCLUSIONS: C1-INH/C4 quantification in DBS can be used for screening of hereditary AE and DNA extracted from dried blood spots is suitable for identifying various types of mutations of the SERPING1 gene.

An HLA-B27 Homodimer Specific Antibody Recognizes a Discontinuous Mixed-Disulfide Epitope as Identified by Affinity-Mass Spectrometry.

HLA-B27 homodimer formation is believed to be a hallmark of HLA-B27 associated spondyloarthritides. Recently, we have generated a homodimer-specific monoclonal antibody (HD6) and have demonstrated that HLA-B27 homodimer complexes are present on monocytes of healthy HLA-B27 gene carriers at low levels, with significantly increased levels at active disease. The capability of the HD6 antibody to discriminate between correctly formed HLA-B27 heterotrimers and pathology-associated homodimers is striking and cannot be explained by the primary structure of HLA-B27. We hypothesized that HD6 accesses a unique epitope and used affinity-mass spectrometry for its identification. The HD6 antibody was immobilized on an activated sepharose affinity column, and HLA-B27 homodimer characterized for affinity. The epitope was identified by proteolytic epitope excision and MALDI mass spectrometry, and shown to comprise a discontinuous Cys-203- 257-Cys mixed-disulfide peptide structure that is not accessible in HLA-B27 heterotrimers due to protection by noncovalently linked ß2-microglobulin. The epitope peptides were synthesized by solid phase peptide synthesis, and the two monomeric peptide components, HLA-B27(203-219) and HLA-B27(257-273), as well as the homo- and hetero-dimeric disulfide linked combinations prepared. The affinity binding constants KD towards the antibodies were determined using a surface acoustic wave (SAW) biosensor, and showed the highest affinity with a KD of approximately 40 nM to the HD6 antibody for the (203-219)-SS-(257-273) mixed disulfide epitope. Graphical Abstract ᅟ.

Characterization of oligomerization-aggregation products of neurodegenerative target proteins by ion mobility mass spectrometry.

Protein amyloidogenesis is generally considered to be a major cause of two most severe neurodegenerative disorders, Parkinson's disease (PD) and Alzheimer's disease (AD). Formation and accumulation of fibrillar aggregates and plaques derived from α-synuclein (α-Syn) and ß-amyloid (Aß) polypeptide in brain have been recognized as characteristics of Parkinson's disease and Alzheimer's disease. Oligomeric aggregates of α-Syn and Aß are considered as neurotoxic intermediate products leading to progressive neurodegeneration. However, molecular details of the oligomerization and aggregation pathway(s) and the molecular structure details are still unclear. We describe here the application of ion-mobility mass spectrometry (IMS-MS) to the identification of α-Syn and Aß oligomerization-aggregation products, and to the characterization of different conformational forms. IMS-MS is an analytical technique capable of separating gaseous ions based on their size, shape, and topography. IMS-MS studies of soluble α-Syn and Aß-aggregates prepared by in vitro incubation over several days were performed on a quadrupole time of flight mass spectrometer equipped with a "travelling wave" ion mobility cell, and revealed the presence of different conformational states and, remarkably, truncation and proteolytic products of high aggregating reactivity. These results suggest that different polypeptide sequences may contribute to the formation of oligomeric aggregates of heterogeneous composition and distinct biochemical properties.