Fibers from Hagfish Proteins

Abstract

Hagfishes are marine craniates (animals that contain hard bone or cartilage skull) that produce large amounts of slime [84Dow]. The slime is composed of cells that are made up of threads similar to fibers seen in a silkworm cocoon. These elliptical-shaped cells are produced by highly specialized slime glands. When these gland cells are released into water, they release strands or threads that uncoil and increase the viscosity of the mucus [81Dow]. A typical cell in the hagfish slime is shown in Fig. 42.1. Each cell has threads that are 1–3 μm in diameter and may have lengths up to 60 cm [84Dow, 12Neg]. SDS-PAGE of the threads revealed that the proteins have a molecular weight of about 63,500 Da. Further analyses of the proteins have demonstrated the presence of three components, one major (α) and two minor (β, γ) that have similar molecular weights but different isoelectric values of 7.56, 5.67, and 5.31 for the α, β, and γ, respectively [84Spi]. The amino acid composition of the three components is shown in Table 42.1. The amino acid composition in the hagfish threads were similar to the keratin polypeptides found in humans and rats [84Spi]. Based on X-ray diffraction studies, it was suggested that the hagfish threads could undergo irreversible α–β transition, under large strains as observed in wool keratins [03Fud]. Using a glass microbeam force transducer apparatus, the tensile properties of the hagfish threads in seawater were determined. It was found that the threads had a low initial stiffness of 6.4 MPa (0.06 g/den) but considerably high strength (180 MPa) (1.6 g/den) and low elongation of 2.2 %.