Lupus anticoagulant (LAC) is a well-known laboratory test used to explore potential reasons for the prolongation of phospholipid-dependent coagulation tests. An extended clotting time in a coagulation test typically suggests a bleeding tendency, as the plasma takes longer to clot. However, a positive LAC result, defined as normalization of prolonged clotting time by adding anionic phospholipids in the system, does not necessarily imply this. In fact, quite the opposite is true: a positive LAC often strongly correlates with an increased risk of thromboembolic events. Therefore, despite being conceptually counterintuitive, LAC remains extremely valuable in routine clinical practice for identifying individuals at risk for thromboembolic events. Over the years, various factors have been recognized as potential inducers of LAC, with antiphospholipid antibodies associated with antiphospholipid syndrome (APS) playing a significant role. Today, research indicates that, among antiphospholipid antibodies, those targeting plasma proteins β-glycoprotein I and prothrombin are central to LAC. This article offers a historical perspective on LAC, emphasizing recent developments in antiprothrombin antibodies, their connection to LAC, and novel detection methods. Our premise is that a deeper understanding of how antiprothrombin antibodies contribute to LAC and the identification of subpopulations of these antibodies potentially responsible for it in thrombotic APS patients could lead to transformative advancements, offering new strategies for risk stratification and personalized treatments for patients with APS and beyond.

The Certified Reference Material (CRM) ERM-DA477/IFCC is a new polyclonal IgG anti-beta2-glycoprotein I (anti-β2GPI) material for the harmonization of the laboratory diagnosis of antiphospholipid syndrome (APS). We evaluated CRM’s ability to represent the heterogeneity of APS patient anti-β2GPI antibodies and to calibrate IgG anti-β2GPI methods.

Protein disulfide isomerase (PDI) is a promising target for combating thrombosis. Extensive research over the past decade has identified numerous PDI-targeting compounds. However, limited information exists regarding how these compounds control PDI activity, which complicates further development.

Hereditary angioedema is an autosomal dominant disorder caused by defects in C1-esterase inhibitor (C1-INH), resulting in poorly controlled activation of the kallikrein-kinin system and bradykinin overproduction. C1-INH is a heavily glycosylated protein in the serine protease inhibitor (SERPIN) family, yet the role of these glycosylation sites remains unclear. To elucidate the functional impact of N-glycosylation in the SERPIN domain of C1-INH, we engineered 4 sets consisting of 26 variants at or near the N-linked sequon (NXS/T). Among these, 6 are reported in patients with hereditary angioedema and 5 are known C1-INH variants without accessible clinical histories. We systematically evaluated their expression, structure, and functional activity with C1s̄, FXIIa, and kallikrein. Our findings showed that of the 11 reported variants, 7 were deleterious. Deleting N at the 3 naturally occurring N-linked sequons (N238, N253, and N352) resulted in pathologic consequences. Altering these sites by substituting N with A disrupted N-linked sugar attachment, but preserved protein expression and function. Furthermore, an additional N-linked sugar generated at N272 impaired C1-INH function. These findings highlight the importance of N-linked sequons in modulating the expression and function of C1-INH. Insights gained from identifying the pathological consequences of N-glycan variants should assist in defining more tailored therapy.

The partner and localizer of BRCA2 (PALB2) is a scaffold protein linking BRCA1 with BRCA2 and RAD51 during homologous recombination (HR). PALB2 interaction with DNA strongly enhances HR in cells, while the PALB2 DNA-binding domain (PALB2-DBD) supports DNA strand exchange . We determined that PALB2-DBD is intrinsically disordered beyond a single N-terminal α-helix. Coiled-coil mediated dimerization is stabilized by interaction between intrinsically disordered regions (IDRs) leading to a 2-fold structural compaction. Single-stranded (ss)DNA binding promotes additional structural compaction and protein tetramerization. Using confocal single-molecule FRET, we observed bimodal and oligomerization-dependent compaction of ssDNA bound to PALB2-DBD, suggesting a novel strand exchange mechanism. Bioinformatics analysis and preliminary observations indicate that PALB2 forms protein-nucleic acids condensates. Intrinsically disordered DBDs are prevalent in the human proteome. PALB2-DBD and similar IDRs may use a chaperone-like mechanism to aid formation and resolution of DNA and RNA multichain intermediates during DNA replication, repair and recombination.