Systematic mapping of the conformational landscape and dynamism of soluble fibrinogen

BACKGROUND

Fibrinogen is a soluble, multisubunit, and multidomain dimeric protein, which, upon its proteolytic cleavage by thrombin, is converted to insoluble fibrin, initiating polymerization that substantially contributes to clot growth. Fibrinogen contains numerous, transiently accessible "cryptic" epitopes for hemostatic and immunologic proteins, suggesting that fibrinogen exhibits conformational flexibility, which may play functional roles in its temporal and spatial interactions. Hitherto, there have been limited integrative approaches characterizing the solution structure and internal flexibility of fibrinogen.

METHODS

Here, utilizing a multipronged, biophysical approach involving 2 solution-based techniques, temperature-dependent hydrogen-deuterium exchange mass spectrometry and small angle X-ray scattering, corroborated by negative stain electron microscopy, we present a holistic, conformationally dynamic model of human fibrinogen in solution.

RESULTS

Our data reveal 4 major and distinct conformations of fibrinogen accommodated by a high degree of internal protein flexibility along its central scaffold. We propose that the fibrinogen structure in the solution consists of a complex, conformational landscape with multiple local minima. This is further supported by the location of numerous point mutations that are linked to dysfibrinogenemia and posttranslational modifications, residing near the identified fibrinogen flexions.

CONCLUSION

This work provides a molecular basis for the structural "dynamism" of fibrinogen that is expected to influence the broad swath of its functionally diverse macromolecular interactions and fine-tune the structural and mechanical properties of blood clots.

Is it possible to predict post-adenotonsillectomy hemorrhage in children with preoperative blood tests? Single-center retrospective study

Introduction: Post-adenotonsillectomy (PAT) bleeding, a life-threatening surgical complication, remains unpredictable despite preoperative blood tests. Every surgeon would like predictive markers for this complication of one of the most common procedures performed in pediatric ear, nose, and throat (ENT). Objective: The purpose of the study is to see whether the results of the blood tests we perform routinely preoperatively in children undergoing adenotonsillectomy (AT) (lymphocyte count and percentage, C reactive protein, fibrinogen, or coagulation variables International Normalized Ratio and activated partial thromboplastin time) can potentially predict early post-AT bleeding. Focus has been placed on the presence of relative lymphocytosis (a value of lymphocyte percentage above 55%) in the blood cell count of the patients and its possible connection to postoperative hemorrhage. Method: We conducted an observational retrospective study on 801 children undergoing adenoidectomy, tonsillectomy, or AT over a period of 6 months in our ENT department. Statistical analysis was performed to compare the data. Results: we did not find a statistically significant correlation between preoperative blood markers (coagulation or inflammatory) and early post-AT bleeding. An important blood marker in relation to PAT bleeding appears to be relative lymphocytosis. Relative lymphocytosis has a weak predictive value of early postoperative bleeding in children with AT (sensitivity of only 31.58%, but acceptable specificity of above 80%). In other words, 80% of patients without relative lymphocytosis will not bleed in the first 24 h postoperatively. Children with relative lymphocytosis may need tighter surveillance in the first 24 h after AT. Conclusions: Relative lymphocytosis has a weak predictive value of early postoperative bleeding in children with AT children.