John M. Beale

Molecular Mechanochemistry: Low Force Switch Slows Enzymatic Cleavage of Human Type I Collagen Monomer

In vertebrate animals, fibrillar collagen accumulates, organizes, and persists in structures which resist mechanical force. This antidissipative behavior is possibly due to a mechanochemical force-switch which converts collagen from enzyme-susceptible to enzyme-resistant. Degradation experiments on native tissue and reconstituted fibrils suggest that collagen/enzyme kinetics favor the retention of loaded collagen. We used a massively parallel, single molecule, mechanochemical reaction assay to demonstrate that the effect is derivative of molecular mechanics. Tensile loads higher than 3 pN dramatically reduced (10×) the enzymatic degradation rate of recombinant human type I collagen monomers by Clostridium histolyticum compared to unloaded controls. Because bacterial collagenase accesses collagen at multiple sites and is an aggressive cleaver of the collagen triple helical domain, the results suggest that collagen molecular architecture is generally more stable when mechanically strained in tension. Thus the tensile mechanical state of collagen monomers is likely to be correlated to their longevity in tissues. Further, strain-actuated molecular stability of collagen may constitute the fundamental basis of a smart structural mechanism which enhances the ability of animals to place, retain, and load-optimize material in the path of mechanical forces.

Metabolic products of microorganisms. 245. Colabomycins, new antibiotics of the manumycin group from Streptomyces griseoflavus. II. Structure of colabomycin A.

The structure of colabomycin A (1) was elucidated by a detailed spectroscopic analysis. Two-dimensional NMR spectroscopy experiments provided assignments of the proton and carbon resonances of the tetraene carboxamide chains occurring in 1. The configurations of eight out of nine double bonds were determined by analysis of their coupling constants. The absolute configurations of C-4 (4S), C-5 (5R) and C-6 (6S) were established from the CD spectra of the parent compound and of 2-(6-oxo-2, 4-hexadienoylamino)-5, 6-epoxy-1, 4-benzoquinone (2), which was obtained from 1 by mild chromic acid oxidation.

The biosynthesis of manumycin; origin of the oxygen and nitrogen atoms

Feeding experiments with sodium [1-13C, 18O2]acetate and [2-13C,15N]glycine, as well as fermentation of Streptomyces parvulus(strain Tu 64) in an atmosphere containing 18O2, produced labelled manumycin (1) samples, whose n.m.r. analysis provided information about the biosynthetic origins of the hetroatoms in this antibiotic.

Diversions of the Shikimate Pathway — The Biosynthesis of Cyclohexanecarboxylic Acid

The shikimic acid pathway1 has evolved in plants and microorganisms to provide for the synthesis of the aromatic amino acids, phenylalanine, tyrosine and tryptophan, as well as a number of other essential aromatic compounds, e.g., jo-aminobenzoic acid, the precursor of folic acid, or]D-hydroxybenzoic acid, the precursor of ubiquinone. A vast number of secondary metabolites, e.g., alkaloids or phenylpropanoids, are derived from these aromatic end products of the pathway. In addition, nature has invented a variety of diversions along the pathway which lead to a range of additional natural products. While the majority of secondary metabolites are derived from late segments of the shikimate pathway, at or beyond the stage of the branch point intermediate, chorismate, a few diversions also occur in the prechorismate part of the pathway. One of these, the reduction of shikimic acid to cyclohexanecarboxylic acid, forms the topic of this chapter.