Glycosylation: a tool for engineering protein based materials

Abstract

Biofilms are bacterial communities formed by adhesion of cells to each other via extracellular matrix. Proteins, one of the components of biofilm matrix, can form fibers and have properties enabling their use as materials. Bacillus subtilis biofilm major protein TasA is a fiber forming non-amyloidogenic protein providing biofilm rigidity. Glycosylation is a post-translational modification observed in all domains of life where sugar groups are added on proteins covalently. Campylobacter jejuni glycosylation is the first bacterial N-linked glycosylation discovered and the most studied system where a heptasaccharide is attached to protein. C. jejuni glycosylation has variety of functions among adhesion, protease resistance and thermal stability. Glycosylation may become an additional method for engineering biofilm proteins as materials with unique properties. For this purpose, we examined effect of glycosylation on structure of natively non-glycosylated proteins by glycosylating alkaline phosphatase enzyme (ALP) at different locations on the protein. Interestingly, phosphatase activity assay showed slight increase in ALP activity on pure proteins glycosylated at the C-terminus. Next, TasA protein was glycosylated at the C-terminus. Glycosylation had no significant effect on fibrillation of TasA in vitro. Secondary structure analysis using circular dichroism data revealed shift from antiparallel to helix structure with glycosylation. Quartz crystal microbalance experiments indicated increased adhesive properties on glycosylated TasA protein on gold. Its application possibility as cell adhesive was assessed by visualizing surface coverage of polystyrene cell culture plate under scanning electron microscope. As a consequence, glycosylation was used as an engineering method for protein-based material development for the first time.