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The functions of the alphaC domains of fibrinogen in clotting and fibrinolysis, which have long been enigmatic, were determined using recombinant fibrinogen truncated at Aalpha chain residue 251. Scanning electron microscopy and confocal microscopy revealed that the fibers of alpha251 clots were thinner and denser, with more branch points than fibers of control clots. Consistent with these results, the permeability of alpha251 clots was nearly half that of control clots. Together, these results suggest that in normal clot formation, the alphaC domains enhance lateral aggregation to produce thicker fibers. The viscoelastic properties of alpha251 fibrin clots differed markedly from control clots; alpha251 clots were much less stiff and showed more plastic deformation, indicating that interactions between the alphaC domains in normal clots play a major role in determining the clot's mechanical properties. Comparing factor XIIIa cross-linked alpha251 and control clots showed that gamma chain cross-linking had a significant effect on clot stiffness. Plasmin-catalyzed lysis of alpha251 clots, monitored with both macroscopic and microscopic methods, was faster than lysis of control clots. In conclusion, these studies provide the first definitive evidence that the alphaC domains play an important role in determining the structure and biophysical properties of clots and their susceptibility to fibrinolysis.

The peptide antibiotic ramoplanin is highly effective against several drug-resistant gram-positive bacteria, including vancomycin-resistant Enterococcus faecium (VRE) and methicillin-resistant Staphylococcus aureus (MRSA), two important opportunistic human pathogens. Ramoplanin inhibits bacterial peptidoglycan (PG) biosynthesis by binding to Lipid intermediates I and II at a location different than the N-acyl-D-Ala-D-Ala dipeptide site targeted by vancomycin. Lipid I/II capture physically occludes these substrates from proper utilization by the late-stage PG biosynthesis enzymes MurG and the transglycosylases. Key structural features of ramoplanin responsible for antibiotic activity and PG molecular recognition have been discovered by antibiotic semisynthetic modification in conjunction with NMR analyses. These results help define a minimalist ramoplanin pharmacophore and introduce the possibility of generating ramoplanin-derived peptide or peptidomimetic antibiotics for use against VRE, MRSA, and related pathogens.

Plasma fibrinogen is a mixture of multiple molecular forms arising mainly through alternative mRNA processing and subsequent posttranslational modification. Recombinant fibrinogen is synthesized without alternative mRNA processing in a cultured cell system that may generate novel posttranslational modifications. Thus, to show that recombinant fibrinogen can serve as a functional model for plasma fibrinogen, we have examined the conversion of fibrinogen to fibrin, comparing the recombinant with the plasma protein. We examined the kinetics of (1) thrombin-catalyzed fibrinopeptide release, (2) thrombin-catalyzed polymerization of fibrinogen, (3) the polymerization of fibrin monomers, and (4) FXIIIa-catalyzed cross-link formation. We saw small differences in polymerization, suggesting that the ordered assembly of protofibrils and fibers was not identical. In all other analyses, we found that plasma fibrinogen and recombinant fibrinogen were remarkably similar. Using electron microscopy, we examined the structures of individual fibrinogen molecules and fibrin clots. Individual fibrinogen molecules were predominantly three nodule structures for both recombinant and plasma proteins. Both samples also displayed four nodule structures, but fewer four nodule structures were found with recombinant fibrinogen. Fibrin clot structures were essentially indistinguishable. We concluded that recombinant fibrinogen can serve as a accurate model for plasma fibrinogen.