The universal structural role of collagen fiber networks has motivated the development of collagen gels, films, coatings, injectables, and other formulations. However, reported synthetic collagen fiber fabrication schemes have either culminated in short, discontinuous fiber segments at unsuitably low production rates, or have incompletely replicated the internal fibrillar structure that dictates fiber mechanical and biological properties. We report a continuous extrusion system with an off-line phosphate buffer incubation step for the manufacture of synthetic collagen fiber. Fiber with a cross-section of 53±14 by 21±3 µm and an ultimate tensile strength of 94±19 MPa was continuously produced at 60 m/hr from an ultrafiltered monomeric collagen solution. The effect of collagen solution concentration, flow rate, and spinneret size on fiber size was investigated. The fiber was further characterized by microdifferential scanning calorimetry, transmission electron microscopy (TEM), second harmonic generation (SHG) analysis, and in a subcutaneous murine implant model. Calorimetry demonstrated stabilization of the collagen triple helical structure, while TEM and SHG revealed a dense, axially aligned D-periodic fibril structure throughout the fiber cross-section. Implantation of glutaraldehyde crosslinked and non-crosslinked fiber in the subcutaneous tissue of mice demonstrated limited inflammatory response and biodegradation after a 6-week implant period.

Insertion and deletion of small heteroduplex loops are common mutations in DNA, but why some loops are prone to mutation and others are efficiently repaired is unknown. Here we report that the mismatch recognition complex, MSH2/MSH3, discriminates between a repair-competent and a repair-resistant loop by sensing the conformational dynamics of their junctions. MSH2/MSH3 binds, bends, and dissociates from repair-competent loops to signal downstream repair. Repair-resistant Cytosine-Adenine-Guanine (CAG) loops adopt a unique DNA junction that traps nucleotide-bound MSH2/MSH3, and inhibits its dissociation from the DNA. We envision that junction dynamics is an active participant and a conformational regulator of repair signaling, and governs whether a loop is removed by MSH2/MSH3 or escapes to become a precursor for mutation.

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High-mobility group B (HMGB) proteins bind duplex DNA without sequence specificity, facilitating the formation of compact nucleoprotein structures by increasing the apparent flexibility of DNA through the introduction of DNA kinks. It has remained unclear whether HMGB binding and DNA kinking are simultaneous and whether the induced kink is rigid (static) or flexible. The detailed molecular mechanism of HMGB-induced DNA ‘softening’ is explored here by single-molecule fluorescence resonance energy transfer studies of single yeast Nhp6A (yNhp6A) proteins binding to short DNA duplexes. We show that the local effect of yNhp6A protein binding to DNA is consistent with formation of a single static kink that is short lived (lifetimes of a few seconds) under physiological buffer conditions. Within the time resolution of our experiments, this static kink occurs at the instant the protein binds to the DNA, and the DNA straightens at the instant the protein dissociates from the DNA. Our observations support a model in which HMGB proteins soften DNA through random dynamic binding and dissociation, accompanied by DNA kinking and straightening, respectively.