THE SONIC FRAGMENTATION OF COLLAGEN MACROMOLECULES

Strong non-ideality effects at low protein concentrations: considerations for elongated proteins

A recent investigation was aimed at obtaining structural information on a highly extended protein via SEC-MALS-SAXS. Significantly broadened elution peaks were observed, reminiscent of a phenomenon known as viscous fingering. This phenomenon is usually observed above 50 mg/mL for proteins like bovine serum albumin (BSA). Interestingly, the highly extended protein (Brpt5.5) showed viscous fingering at concentrations lower than 5 mg/mL. The current study explores this and other non-ideal behavior, emphasizing the presence of these effects at relatively low concentrations for extended proteins. BSA, Brpt5.5, and a truncated form of Brpt5.5 referred to as Brpt1.5 are studied systematically using size-exclusion chromatography (SEC), sedimentation velocity analytical ultracentrifugation (AUC), and viscosity. The viscous fingering effect is quantified using two approaches and is found to correlate well with the intrinsic viscosity of the proteins-Brpt5.5 exhibits the most severe effect and is the most extended protein tested in the study. By AUC, the hydrodynamic non-ideality was measured for each protein via global analysis of a concentration series. Compared to BSA, both Brpt1.5 and Brpt5.5 showed significant non-ideality that could be easily visualized at concentrations at or below 5 mg/mL and 1 mg/mL, respectively. A variety of relationships were examined for their ability to differentiate the proteins by shape using information from AUC and/or viscosity. Furthermore, these relationships were also tested in the context of hydrodynamic modeling. The importance of considering non-ideality when investigating the structure of extended macromolecules is discussed.

Effects of Shear Stress Waves on Meat Tenderness: Ultrasonoporation

Meat is an important part of the food pyramid in Mexico, to such an extent that it is included in the basic food basket. In recent years, there has been great interest in the application of so-called emerging technologies, such as high-intensity ultrasound (HIU), to modify the characteristics of meat and meat products. The advantages of the HIU in meat such as pH, increased water-holding capacity, and antimicrobial activity are well documented and conclusive. However, in terms of meat tenderization, the results are confusing and contradictory, mainly when they focus on three HIU parameters: acoustic intensity, frequency, and application time. This study explores via a texturometer the effect of HIU-generated acoustic cavitation and ultrasonoporation in beef (m. Longissimus dorsi). Loin-steak was ultrasonicated with the following parameters: time tHIU = 30 min/each side; frequency fHIU = 37 kHz; acoustic intensity IHIU = ~6, 7, 16, 28, and 90 W/cm2. The results showed that acoustic cavitation has a chaotic effect on the loin-steak surface and thickness of the rib-eye due to Bjerknes force, generating shear stress waves, and acoustic radiation transmittance via the internal structure of the meat and the modification of the myofibrils, in addition to the collateral effect in which the collagen and pH generated ultrasonoporation. This means that HIU can be beneficial for the tenderization of meat.

Bioprinting of Collagen Type I and II via Aerosol Jet Printing for the Replication of Dense Collagenous Tissues

Collagen has grown increasingly present in bioprinting, however collagen bioprinting has mostly been limited to the extrusion printing of collagen type I to form weak collagen hydrogels. While these weak collagen hydrogels have their applications, synthetic polymers are often required to reinforce gel-laden constructs that aim to replicate dense collagenous tissues found in vivo. In this study, aerosol jet printing (AJP) was used to print and process collagen type I and II into dense constructs with a greater capacity to replicate the dense collagenous ECM found in connective tissues. Collagen type I and II was isolated from animal tissues to form solutions for printing. Collagen type I and II constructs were printed with 576 layers and measured to have average effective elastic moduli of 241.3 ± 94.3 and 196.6 ± 86.0 kPa (±SD), respectively, without any chemical modification. Collagen type II solutions were measured to be less viscous than type I and both collagen type I and II exhibited a drop in viscosity due to AJP. Circular dichroism and SDS-PAGE showed collagen type I to be more vulnerable to structural changes due to the stresses of the aerosol formation step of aerosol jet printing while the collagen type II triple helix was largely unaffected. SEM illustrated that distinct layers remained in the aerosol jet print constructs. The results show that aerosol jet printing should be considered an effective way to process collagen type I and II into stiff dense constructs with suitable mechanical properties for the replication of dense collagenous connective tissues.

Effect of Solvent on the Hydrodynamic Properties of Collagen

In this study, the effect of solvent on the hydrodynamic properties of collagen extracted from tail tendons of young rats was researched. Collagen was dissolved in various aqueous carboxylic acid solutions, including acetic acid (AA), acetic acid with the addition of sodium chloride (AA/NaCl), formic acid (FA), lactic acid (LA), citric acid (CA), and also citrate buffer at pH = 3.7 (CB). The properties of collagen solutions at a concentration of 0.45 mg/mL were characterized based on the viscometric method. The reduced viscosity, intrinsic viscosity, and Huggins coefficient of collagen solutions and effect of solvent, temperature, and UV irradiation on these properties were investigated. Collagen solutions in acetic acid, acetic acid/NaCl, and citrate buffer were irradiated with UV light up to 1 h, and the viscosity of collagen solutions was measured. It was found that the organic acids used as solvent affected viscosity behavior, denaturation temperature, and stability of collagen solutions. The lowest values of studied parameters were obtained for the collagen solutions in acetic acid with the addition of sodium chloride. Thus, the effect of various aqueous carboxylic acid solutions on collagen solutions properties and denaturation temperature can also be affected by the sodium chloride addition. The results of this research can be crucial for the preparation of collagen solutions for both cosmetic and biomedical applications.

Conformation of the von Willebrand factor/factor VIII complex in quasi-static flow

Von Willebrand factor (VWF) is a plasma glycoprotein that circulates noncovalently bound to blood coagulation factor VIII (fVIII). VWF is a population of multimers composed of a variable number of ∼280 kDa monomers that is activated in shear flow to bind collagen and platelet glycoprotein Ibα. Electron microscopy, atomic force microscopy, small-angle neutron scattering, and theoretical studies have produced a model in which the conformation of VWF under static conditions is a compact, globular “ball-of-yarn,” implying strong, attractive forces between monomers. We performed sedimentation velocity (SV) analytical ultracentrifugation measurements on unfractionated VWF/fVIII complexes. There was a 20% per mg/ml decrease in the weight-average sedimentation coefficient, s_w, in contrast to the ∼1% per mg/ml decrease observed for compact globular proteins. SV and dynamic light scattering measurements were performed on VWF/fVIII complexes fractionated by size-exclusion chromatography to obtain s_w values and z-average diffusion coefficients, D_z. Molecular weights estimated using these values in the Svedberg equation ranged from 1.7 to 4.1 MDa. Frictional ratios calculated from D_z and molecular weights ranged from 2.9 to 3.4, in contrast to values of 1.1–1.3 observed for globular proteins. The Mark–Houwink–Kuhn–Sakurada scaling relationships between s_w, D_z and molecular weight, s=k′Mas and D=k″MaD, yielded estimates of 0.51 and –0.49 for a_s and a_D, respectively, consistent with a random coil, in contrast to the a_s value of 0.65 observed for globular proteins. These results indicate that interactions between monomers are weak or nonexistent and that activation of VWF is intramonomeric.

The Role of Concentration on Drop Formation and Breakup of Collagen, Fibrinogen, and Thrombin Solutions during Inkjet Bioprinting

The influence of protein concentration on drop formation and breakup of aqueous solutions of fibrous proteins collagen and fibrinogen and globular protein thrombin in different concentration regimes has been investigated during drop-on-demand (DOD) inkjet printing. The capillary-driven thinning and breakup of dilute collagen, fibrinogen, and thrombin solutions, the solutions in which protein molecules are far away from each other, are predominantly resisted by inertial force. Although the capillary-driven thinning and breakup of semidilute unentangled collagen and fibrinogen solutions, the solutions in which protein molecules begin to interpenetrate each other, are predominantly resisted by inertial force on the initial onset of necking, the breakup of droplets is delayed because of the resistance of elastic force. The resistance of viscous force to the necking and breakup of both the dilute and semidilute unentangled protein solutions is negligible. Aggregates or subvisible particles (between 1 and 100 μm) constantly disrupt the formation of droplets for the semidilute unentangled protein solutions, even when their inverse Ohnesorge number (Z) is within the printability range of 4 ≤ Z ≤ 14. Although aggregates are present in the dilute protein solutions, they do not disrupt the formation of droplets.

Rheological investigation of collagen, fibrinogen, and thrombin solutions for drop-on-demand 3D bioprinting

Collagen, fibrinogen, and thrombin proteins in aqueous buffer solutions are widely used as precursors of natural biopolymers in three-dimensional (3D) bioprinting applications. The proteins are sourced from animals and their quality may vary from batch to batch, inducing differences in the rheological properties of such solutions. In this work, we investigate the rheological response of collagen, fibrinogen, and thrombin protein solutions in bulk and at the solution/air interface. Interfacial rheological measurements show that fibrous collagen, fibrinogen and globular thrombin proteins adsorb and aggregate at the solution/air interface, forming a viscoelastic solid film at the interface. The viscoelastic film corrupts the bulk rheological measurements in rotational rheometers by contributing to an apparent yield stress, which increases the apparent bulk viscosity up to shear rates as high as 1000 s^-1. The addition of a non-ionic surfactant, such as polysorbate 80 (PS80) in small amounts between 0.001 and 0.1 v/v%, prevents the formation of the interfacial layer, allowing the estimation of true bulk viscosity of the solutions. The estimation of viscosity not only helps in identifying those protein solutions that are potentially printable with drop-on-demand (DOD) inkjet printing but also detects inconsistencies in flow behavior among the batches.

A natural deep eutectic solvent (NADES) as potential excipient in collagen-based products

Natural deep eutectic solvents (NADES) have previously shown antibacterial properties alone or in combination with photosensitizers and light. In this study, we investigated the behavior of the structural protein collagen in a NADES solution. A combination of collagen and NADES adds the unique wound healing properties of collagen to the potential antibacterial effect of the NADES. The behavior of collagen in a NADES composed of citric acid and xylitol and aqueous dilutions thereof was assessed by spectroscopic, calorimetric and viscosity methods. Collagen exhibited variable unfolding properties dependent on the type of material (telo- or atelocollagen) and degree of aqueous dilution of the NADES. The results indicated that both collagen types were susceptible to unfolding in undiluted NADES. Collagen dissolved in highly diluted NADES showed similar results to collagen dissolved in acetic acid (i.e., NADES network possibly maintained). Based on the ability to dissolve collagen while maintaining its structural properties, NADES is regarded as a potential excipient in collagen-based products. This is the first study describing the solubility and structural changes of an extracellular matrix protein in NADES.

Novel DNPH-based method for determination of protein carbonylation in muscle and meat

Protein oxidation is considered an ongoing deteriorative process during storage of fresh and processed meat. Carbonyl compounds have traditionally been detected spectrophotometrically after derivatization with 2,4-dinitrophenylhydrazine (DNPH) to form protein-bound hydrazones with absorbance at 370 nm. Here we describe a novel DNPH-based method to quantify protein carbonylation in muscle and meat. The additional steps of the novel method aimed at increasing the protein solubility and inducing protein unfolding before labeling with DNPH. Compared to the traditional method, the new procedure reflected an increased protein carbonylation level measuring overall two to fourfold more carbonyls in muscles from different species as well as in soluble, salt-soluble and insoluble protein fractions. The study suggested that protein unfolding is a more important phenomenon than solubilization for increased DNPH labeling. The novel method resulted in three to fourfold larger carbonyl content determined in chicken, pork and beef (2.8, 3.6 and 3.1 nmol/mg of protein, respectively).

Analysis of bimodal thermally-induced denaturation of type I collagen extracted from calfskin

DSC tracks of collagen in solution revealing a bimodal behaviour during its heat-induced denaturation.

Collagen oligomers modulate physical and biological properties of three-dimensional self-assembled matrices

Elucidation of mechanisms underlying collagen fibril assembly and matrix-induced guidance of cell fate will contribute to the design and expanded use of this biopolymer for research and clinical applications. Here, we define how Type I collagen oligomers affect in-vitro polymerization kinetics as well as fibril microstructure and mechanical properties of formed matrices. Monomers and oligomers were fractionated from acid-solubilized pig skin collagen and used to generate formulations varying in monomer/oligomer content or average polymer molecular weight (AMW). Polymerization half-times decreased with increasing collagen AMW and closely paralleled lag times, indicating that oligomers effectively served as nucleation sites. Furthermore, increasing AMW yielded matrices with increased interfibril branching and had no correlative effect on fibril density or diameter. These microstructure changes increased the stiffness of matrices as evidenced by increases in both shear storage and compressive moduli. Finally, the biological relevance of modulating collagen AMW was evidenced by the ability of cultured endothelial colony forming cells to sense associated changes in matrix physical properties and alter vacuole and capillary-like network formation. This work documents the importance of oligomers as another physiologically-relevant design parameter for development and standardization of polymerizable collagen formulations to be used for cell culture, regenerative medicine, and engineered tissue applications.

Liquid crystalline collagen: a self-assembled morphology for the orientation of mammalian cells

We report the creation of collagen films having a cholesteric banding structure with an orientation that can be systematically controlled. The action of hydrodynamic flow and rapid desiccation was used to influence the orientation of collagen fibrils, producing a film with a twisted plywood architecture. Adult human fibroblasts cultured on these substrates orient in the direction of the flow deposition, and filopodia are extended onto individual bands. Atomic force microscopy reveals the assembly of 30 nm collagen fibrils into the uniform cholesteric collagen films with a periodic surface relief. The generation of collagen with a reticular, "basket-weave" morphology when using lower concentrations is also discussed.

The effect of ultraviolet irradiation on soluble collagen

1. The effect of ultraviolet irradiation on acid-soluble and neutral-salt-soluble calf-skin collagen was studied by chromatography, gel filtration, amino acid analysis and sedimentation of the sub-units, and the reaction kinetics of degradation were obtained from viscosity and optical rotation measurements. 2. It was demonstrated that, whereas the structure of neutral-salt-soluble calf-skin collagen may be represented by the formula (alpha(1))(2)alpha(2), the acid-soluble extract has the formula alpha(1).(alpha(2))(2). The acid-soluble collagen is also unusual in containing a large amount of a component that could be beta(22). 3. Ultraviolet irradiation causes the progressive degradation of the collagen molecule into smaller molecular fragments that subsequently lose their helical nature. The rate constants show that the denaturation of soluble collagens by ultraviolet irradiation is much slower, under the conditions used, than denaturation by heat or enzymes.

THERMAL DENATURATION OF SOLUBLE CALF-SKIN COLLAGEN

1. Soluble calf-skin collagen has been denatured thermally between 37 degrees and 60 degrees and the component proteins have been separated on carboxymethylcellulose. 2. Four main fractions have been separated; alpha and beta (in the nomenclature in common usage) and two other fractions. (The alpha and beta components are complex owing to the presence of alpha(1), alpha(2), beta(1) and beta(2) parts). 3. Fractions 3 and 4 undergo rapid denaturation between 39 degrees and 40 degrees whereafter fraction 4 remains virtually unchanged even at 60 degrees . 4. That portion of fraction 4 which remains at 60 degrees is thought to be identical with the fraction designated gamma by other workers, this fraction being composed of three alpha-chains in covalent linkage (such bonds are alkali-labile). 5. The equilibrium between alpha, beta and fractions 3 and 4 is apparently reversible since acid-soluble collagen after denaturation at 45 degrees or 60 degrees followed by cooling to 0 degrees for 30min. was found to contain only fraction 4 when chromatographed at 37 degrees .

The Effect of Ultrasound on the Healing of Repaired Cockerel Tendon: Is Collagen Crosslinkage a Factor?

The acid solubility of the collagen of cockerel tendon demonstrates a similar degree of intermolecular acid-labile cross-linkage to that found in adult human tendon, implying similar maturity of the collagen. By contrast, rabbit tendon collagen demonstrates a dissimilar degree of cross-linkage suggesting immaturity of the collagen. Since this cross-linkage is likely to be related to mechanical properties, the cockerel may well be a better animal model than the rabbit for the study of tendon healing.

The application of ultrasound to sutured cockerel tendons produced no change in the mechanical strength of the tendon at six weeks, or its propensity to form adhesions, relative to untreated control sutured tendons. This contrasts with the decrease in strength after ultrasound found by previous workers using rabbits.

Hydroxyproline-rich bacterial agglutinin from potato : extraction, purification, and characterization

A protein, extracted from Katahdin potato (Solanum tuberosum L. cv ;Katahdin') tubers and purified by ion exchange chromatography and gel filtration, agglutinates avirulent strains of the bacterial wilt pathogen, Pseudomonas solanacearum, but only weakly agglutinates virulent strains. The agglutinin has very low hemagglutinating activity (in contrast to potato lectin) and is a glycoprotein containing about 61% carbohydrate. The carbohydrate moiety contains 91% (weight%) arabinose, 5% galactose, 3% glucose, and 1% glucosamine. The protein portion is rich in hydroxyproline (42%), lysine (16%), serine (9%), and proline (9%). The entire agglutinin has a molecular weight of 91,000 +/- 5,000 and is very basic (pI > 11). Shape estimations based on the concentration dependence of the sedimentation coefficient, the high viscosity ([eta] = 92.7), the frictional coefficient (f/f(o) = 2.15), and axial ratio (a/b = 25) indicate that the agglutinin is a prolate ellipsoid.

Some physical and chemical properties of trypsin-digested nucleoprotein

A DNA-peptide complex that is soluble in 0.2m-sodium chloride can be prepared by trypsin digestion of calf thymus nucleoprotein. The trypsin-digested nucleoprotein molecule contains about 70% of DNA and 30% of peptides by weight, and consists of one DNA molecule associated with arginine-rich peptides. A series of trypsin-digested nucleoprotein preparations differing only in molecular weight were prepared by blending. The intrinsic viscosity and average sedimentation coefficient were determined for each of these preparations. Then the DNA was isolated from each preparation and the hydrodynamic measurements were repeated on the DNA. From a comparison of these results it was concluded that the presence of the complex-forming peptides causes a large decrease in intrinsic viscosity of the DNA and an increase in sedimentation coefficient. In addition, the hydrodynamic data indicate that the DNA-peptide complex behaves like a coil in solution but is more compact than the same length of DNA. The ;melting' profiles, streptomycin precipitation curves and maximum viscosities obtained with ethidium bromide binding for the trypsin-digested nucleoprotein are similar to those of purified DNA, and markedly different from those of undigested nucleoprotein. These findings suggest that the peptides are not strongly associated with the DNA, and that secondary valency forces are involved in the binding.

Purification and properties of an acidic protein from chromaffin granules of bovine adrenal medulla

1. A soluble protein has been purified from an aqueous extract of bovine adrenal chromaffin granules by chromatography on Sephadex G-200. This protein comprises 25% of the total protein of the granules and gave a single band on gel electrophoresis. 2. The protein is unusually rich in acidic amino acids, notably glutamic acid (26.0%, w/w); it is also relatively rich in proline (8.6%, w/w) but poor in cystine (0.35%, w/w). 3. A molecular weight of 77000 was obtained from sedimentation and diffusion measurements on the protein, and approach-to-equilibrium measurements gave apparent molecular weights of the same order. 4. A molecular weight 7 times that given above was estimated from the results of chromatography on a column of Sephadex G-200 that had been calibrated with globular proteins. However, good agreement between the ultracentrifuge and Sephadex experiments was obtained on the assumption that Sephadex chromatography depends on the effective hydrodynamic radii of proteins and not on their molecular weights. 5. The hydrodynamic properties of the protein differed from those of a typical globular protein. Thus the protein had a high intrinsic viscosity, a high frictional ratio and a large effective hydrodynamic volume. 6. The hydrodynamic properties of the protein, but not its molecular weight, were dependent on the ionic strength of the solvent. Increasing the ionic strength caused an increase in the sedimentation and diffusion coefficients, but a decrease in the intrinsic viscosity and in the frictional ratio of the protein. 7. Optical-rotatory-dispersion measurements indicated that only a small part of the polypeptide chain was in an alpha-helical conformation. 8. These results are compatible with the protein's having a conformation approaching that of a random-coil polypeptide, the volume occupied by the molecule being determined by electrostatic repulsion between the excess of negative charges.

Sonic Energy Effects in Bovine Serum Albumin Solutions

Bovine serum solutions exposed to high-frequency sound were examined by ultracentrifugal, electrophoretic, viscometric, conductivity, light scattering, and optical rotatory dispersion procedures. Parameters determined with treated material were the same as those determined with untreated albumin solutions except for slight differences in rotation, the dispersion constant, and in weight-average molecular weight.