W. Folkhard

Stress-induced molecular rearrangement in tendon collagen

Tension-induced molecular rearrangements in wet native fibres of rat-tail tendons and human finger flexor tendons are registered with the help of time-resolved diffraction spectra using synchrotron radiation. The tension-induced increase of the 67 nm D period is combined with changes in the intensities of some orders of the meridional small angle reflection. Both effects are reversible when unloading the fibre, but are preserved when the load is held constant until the fibre tears. The increase in the D period is partly due to a sliding of the triple helices relative to each other and partly due to a stretching of the triple helices themselves. The sliding of the triple helices results in an alteration of the D stagger, leading to a change in the length of the gap and overlap regions, and to a stretching of the cross-linked telopeptides. This interpretation is supported by comparison with the relative intensities derived from a model with varying length of gap and overlap regions, as well as by comparison with model calculations that include the telopeptides.

Quantitative analysis of the molecular sliding mechanisms in native tendon collagen — time-resolved dynamic studies using synchrotron radiation

Abstract The stretching of native fibres from rat tail tendons (RTT) was monitored in time-resolved X-ray measurements using synchotron radiation, by registering one meridional small angle diffraction pattern every second. The time course of this dynamic molecular process was analyzed quantitatively with the help of model calculations based on the amino acid sequence. The results show that two mechanisms contribute to the elongation of fibrils, namely the stretching of the collagen triple helices and their sliding relative to each other (increase of the D stagger). The results further show that these two processes do not take place simultaneously. The first increase of the D period from 67.0 nm to about 67.6 nm is correlated with a stretching of the triple helices. The further increase of the D period is due to a continuous increase of the D stagger. This succession is independent of the age of the animals and also independent of the stretching velocity. The stretching process is shown to be reversible at the molecular level up to a D period of about 68.4 nm.

Structural dynamic of native tendon collagen

The dynamic behaviour of collagen fibrils is revealed by time-resolved X-ray investigations of native rat tail tendon fibres in tensile tests.

Structure of F-pili: reassessment of the symmetry.

Reassessment of the X-ray fibre diffraction patterns of F-pili using a more accurate subunit molecular weight suggests that subunits in F-pili are related by a fivefold rotation axis around the pilus axis. The identity of this fivefold symmetry with the fivefold rotation axis that relates the subunits in fd bacteriophage supports a simple model for tip-to-tip adsorption of bacteriophage to pili.

New aspects of the etiology of tendon rupture

SummaryNative collagen fibers were exposed to different dynamic loads to simulate damage to tendons and ligaments relevant clinically and for sports medicine. The results suggest that the rupture of a tendon is caused at the submicroscopic fibrillar level. Not only slow or very fast elongation, but also very fast unloading of stretched fibers seems to be responsible for disseminated damage, which reduces the stability of a fiber. This damage is induced by intrafibrillar sliding processes, which occur only a few seconds before macroscopic slippage takes place. The significance of these events for the beginning and progress of repair in vivo is discussed. The conclusions are supported by simultaneous mechanical and radiological measurements, as well as by light- and electron-microscopic results.ZusammenfassungZur Simulierung klinisch bzw. sportmedizinisch relevanter Schäden an Sehnen und Bändern wurden native Kollagenfasern unterschiedlichen dynamischen Belastungen ausgesetzt. Die erzielten Ergebnisse sprechen dafür, die Ursachen einer Sehnenruptur im submikroskopischen fibrillären Bereich zu suchen. Sowohl eine langsame oder ruckartige Dehnung als auch eine ruckartige Entlastung zugbelasteter Fasern scheinen für das Auftreten disseminierter, die Faserstabilität reduzierender Gefügestörungen verantwortlich zu sein. Diese Gefügestörungen werden durch intrafibrilläre Gleitvorgänge eingeleitet, die an den noch voll belastbaren Fasern nur wenige Sekunden vor dem Einsetzen eines makroskopischen Faserfließens auftreten. Die Bedeutung dieser Ereignisse für den Beginn und Verlauf einer in vivo stattfindenden Reparationsphase wird erörtert. Die Aussagen werden gestützt durch simultane mechanische und röntgenographische Messungen sowie durch makroskopische, licht- und elektronenmikroskopische Befunde.

Packing of collagen molecules modified with 2-propanol.

X-ray diffraction data of collagen molecules modified with 2-propanol favour a quasi-hexagonal lateral packing over a quasi-tetragonal one.

Ehlers-Danlos syndrome type IV (EDS IV) as model of a defective biopolymer composite material.

The connective tissue of a lethal EDS IV case was investigated for the reasons of the manifested disturbances of the arterial wall. This functional disorder was attributed to the mechanical decoupling of elastin and collagen, with the premise of a composite material consisting of cellular, fibrillar, lamellar and other matrix components. A conceivable relation between the manifested deficiency of type III collagen and a disturbed anchoring of elastin is shown. These findings are supported by biochemical, morphological, x-ray and mechanical data.

Strukturdynamik nativer und künstlich vernetzter Sehnenfasern

Die Strukturdynamik von Sehnenfasern, d. h. die Ermittlung bestimmter Parameter an in Bewegung befindlichen Kollagenmolekulen, wird an nativen und an mit Hexamethylendiisocyanat (HMDI) kunstlich vernetzten Sehnenfasern aufgezeigt. Das Ziel dieser Untersuchungen ist die analytische Erfassung und Lokalisation kunstlich eingefuhrter Querbrucken mit Aussagewert fur naturlicherweise vorkommende Vernetzungen. Voraussetzung hierfur ist der Einsatz neuer Technologien, so z. B. der Synchrotronstrahlung zur Erzeugung von Rontgenmesdaten sehr schnell ablaufender dynamischer Vorgange sowie die uberraschende Tatsache, das mit HMDI vernetzte Fasern ein von nativen Objekten nicht unterscheidbares Rontgendiagramm liefern.

Exchange of the Structural Water and Molecular Dynamic in Collagen

Water has been found to be essential in the maintainance of collagen in its native conformation and is considered as an integral element of the collagen structure. The collagen triple helix differs from both the α-helix and the β-sheet structures in that not all hydrogen bonding sites on the backbone are occupied within the macromolecular structure. Only every third C=O and NH group of the backbone is involved in intramolecular hydrogen bonding. Water molecules stabilize the triple helical structure by intramolecular bridges by binding to the unoccupied hydrogen donor and acceptor groups on the protein backbone (Traub 1971; Ramachandran 1976).

Hydratwasseraustausch und Alkanol-induzierte Molekulare Umordnungen an Kollagen/Exchange of the Structural Water of Collagen and Alcanol-Induced Molecular Rearrangement

The exchange of the structural water of collagen for alcanols was investigated using X -ray diffraction combined with mechanical measurements. The stepwise dehydration with methanol, ethanol or 1-propanol is reflected by the reversible loss of the characteristic equatorial reflexions of native rat tail tendons. The exchange for 1-alcanols in ascending homologous order is characterized by: 1. an increase in the distance between the axes of the triple helices depending on the number of carbon atoms of the alkyl chain, 2. a shortening of the long-spacing of 67 nm characteristic of native collagen and 3. the herewith correlated increase in tension on isometrically measured fibres. The stepwise dehydration with 2-propanol leads first to a loss of the equatorial reflexions that are characteristic of native collagen, then to their reappearance at smaller diffraction angles. The exchange for 2-alcanols in ascending homologous order is characterized by: 1. a splitted equatorial reflexion at 4.1 ± 0 .1 nm, that stays constant up to 2-nonanol, and moves to 4 .8 - 5 .0 ± 0 .1 nm with more than 9 carbon atoms in the alkyl chain, 2. a shortening of the long spacing of 67 nm characteristic of native collagen and 3. the herewith correlated increase in tension on isometrically measured fibres. Stereochemical requirements are discussed as well as consequences for the structural model of collagen.