Enzymatic phosphorylation of silk fibroins: a platform for the production of biocompatible, cell-static, materials

Abstract

Silks are natural protein polymers produced by insects. Silk heavy chain of B.mori is primarily composed of hydrophobic, –(–Ala–Gly–)n– -sheet crystalline domains. Based on silk biocompatibility, biodegradability and strength, different materials were developed. Silk offers a stabilizing environment for incorporated proteins and molecules. Silk properties can be controlled via structure manipulation, by coupling molecules of biological significance; its Tyr and Ser residues can be modified. Once incorporated into a protein, the phosphate group establishes hydrogen bonds that affect intra- and inter-molecular interactions16. Phosphorylation is stable under physiological conditions, thus directing the formation and reorganization of protein networks. Curiously, using phosphorylation for protein functionalization is largely unexplored. Significant research is devoted to bio-inspired materials with various cell-differentiating and cell-supporting features. However, little attention is paid to develop cell-static bio-materials. Such materials do not promote cell growth. That can be achieved by lowering the probability of cell attachment to the material, via creation of negatively charged material surface. The goal of this study was to produce bio-compatible materials with the cell-static properties by phosphorylation. Silk solutions were made to cast films of variable pH and phosphorylated content. Obtained materials were tested and a dependency between amount of phosphorylation and bio-chemical properties confirmed.