Fibrin (Fb) networks self‐assemble through the coagulation cascade and serve as the structural foundation of blood clots. Following severe trauma or drug therapy, reduced integrity of Fb networks can lead to formation of clots with inadequate mechanical properties. A key feature of therapeutic interventions for hemostasis is therefore the ability to restore mechanical strength to clots formed under coagulopathic conditions. Here, an intrinsically disordered protein based on an elastin‐like polypeptide (ELP) sequence is described, which specifically binds Fb and modulates its mechanical properties. Hemostatic ELPs (hELPs) are designed containing N‐ and C‐terminal peptide tags that are selectivity recognized by human transglutaminase factor XIIIa and covalently linked into fibrin networks via the natural coagulation cascade. Phase separation of hELPs above their lower critical solution temperature leads to stiffening and rescue of clot biophysical properties under simulated conditions of dilutive coagulopathy. In addition to phase‐dependent stiffening, the resulting hELP‐Fb networks exhibit resistance to plasmin degradation, reduced pore sizes, and accelerated gelation rate following initiation of clotting. These results demonstrate the ability of protein‐based phase separation to modulate the physical and biochemical properties of blood clots and suggest protein phase separation as a new mechanism for achieving hemostasis in clinical settings.
The opportunistic
pathogen
Staphylococcus epidermidis
utilizes a multidomain surface adhesin protein to bind host components
and adhere to tissues. While it is known that the interaction between
the SdrG receptor and its fibrinopeptide target (FgB) is exceptionally
mechanostable (∼2 nN), the influence of downstream B domains
(B1 and B2) is unclear. Here, we studied the mechanical relationships
between folded B domains and the SdrG receptor bound to FgB. We used
protein engineering, single-molecule force spectroscopy (SMFS) with
an atomic force microscope (AFM), and Monte Carlo simulations to understand
how the mechanical properties of folded sacrificial domains, in general,
can be optimally tuned to match the stability of a receptor–ligand
complex. Analogous to macroscopic suspension systems, sacrificial
shock absorber domains should neither be too weak nor too strong to
optimally dissipate mechanical energy. We built artificial molecular
shock absorber systems based on the nanobody (VHH) scaffold and studied
the competition between domain unfolding and receptor unbinding. We
quantitatively determined the optimal stability of shock absorbers
that maximizes work dissipation on average for a given receptor and
found that natural sacrificial domains from pathogenic
S. epidermidis
and
Clostridium perfringens
adhesins exhibit stabilities at or near this optimum within a specific
range of loading rates. These findings demonstrate how tuning the
stability of sacrificial domains in adhesive polyproteins can be used
to maximize mechanical work dissipation and serve as an adhesion strategy
by bacteria.
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