Essential role of a carboxyl‐terminal α‐helix motif in the secretion of coagulation factor XI

BackgroundCoagulation factor XI (FXI) is a plasma serine protease zymogen that contributes to hemostasis. However, the mechanism of its secretion remains unclear.ObjectiveTo determine molecular FXI by characterizing novel mutant identified in FXI‐deficient Japanese patient.Patient/MethodsThe gene (F11) was analyzed direct sequencing. Mutant recombinant (rFXI) overexpressed HEK293 or COS‐7 cells. Western blotting and enzyme‐linked immunosorbent assay were performed examine extracellular profile. Immunofluorescence microscopy used investigate subcellular localization rFXI mutant.ResultsWe homozygous frameshift mutation F11 [c.1788dupC (p.E597Rfs*65)], resulting unique extended carboxyl‐terminal (C‐terminal) structure FXI. Although rFXI‐E597Rfs*65 intracellularly synthesized, markedly reduced. Subcellular analysis revealed abnormally retained endoplasmic reticulum (ER). We generated series C‐terminal–truncated mutants further role C‐terminal region secretion. Serial experiments threonine at position 622, fourth residue from C‐terminus, essential for Notably, Thr622 engages formation an α‐helix motif, indicating importance intracellular behavior secretion.ConclusionFXI E597Rfs*65 results pathogenesis severe secretory defect aberrant ER‐to‐Golgi trafficking caused lack motif. This study demonstrates impact structure, especially on