Protein Engineering, Vol. 15, No. 11, 895-902,
November 2002
© 2002 Oxford University Press
Crystine: fibrous biomolecular material from protein crystals cross-linked in a specific geometry
1 Department of Chemistry, Rensselaer Polytechnic Institute, Troy, NY 12180, 3 Nelson Institute of Environmental Medicine, NYU Medical Center, 57 Old Forge Road, Tuxedo Park, NY 10987, 4 Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213 and 5 Wadsworth Center, New York State Department of Health, Albany,NY 12201, USA
Cysteine substitutions were engineered on the surface of maltose binding protein to produce crystine fibers, linear polymers of folded protein formed within a crystal. Disulfide bond formation between adjacent protein molecules within the lattice was monitored by X-ray crystallography. The cross-linked crystals were resistant to dissolution in water or neutral buffer solutions, even though the cross-linking was one-dimensional. However, crystine fibers were observed by transmission electron microscopy to dissociate from the crystals in acidic solutions. Some fibers remained associated as two-dimensional bundles or sheets, with a repeat unit along the fibers consistent with the packing of the individual protein molecules in the crystal. Neutralization of the acidic solutions caused the fibers to re-associate as a solid. Crystine threads were drawn out of this solution. In scanning electron microscopy images, many individual fibers could be seen unwinding from the ends of some threads. Crystine fibers are a new type of biomolecular material with potential applications wherever the use of proteins in a fibrous form is desirable, for example, the incorporation of enzymes into cloth or filtration material.