INTRODUCTION

We have seen in the preceding chapters that elastomeric proteins must firstly contain independent monomeric chains that are flexible and generally conformationally free, and secondly be cross-linked at specific points to form a network to ensure elastic recoil. The elastic properties are modulated by the length and properties of elastic domains, which are in turn delineated by the extent and location of cross-linking. These cross-links tend to form in small ‘crystalline’ domains within a generally amorphous “rubber-like” structure. The ability to control the specific location and nature of the intermolecular cross-links in biological macromolecules has evolved and been widely exploited by organisms throughout the animal kingdom. It has allowed tissues to evolve optimal characteristics of strength and elasticity for protection against the stresses of the environment, since malfunctioning can at worst be lethal. An understanding of these cross-linking mechanisms can provide another dimension to our knowledge of the properties of elastic proteins, and at the same time an insight into the changes in physical properties during growth and maturation. In some instances, the location of the cross-links may also provide data on the alignment of the molecules in the supramacromolecular assemblies involved in elastomeric proteins.

COVALENT CROSS-LINKS

Peroxidase-Induced Di-tyrosine Cross-links

Resilin

The first intermolecular cross-links to be identified in an elastomeric protein were isolated from resilin by Andersen (1964) as di- and tri-tyrosine (Figure 16.1 (see chapter 13)) (Table 16.1).