Sequence-based protein stabilization in the absence of glycosylation

Abstract

Asparagine-linked N-glycosylation is a common modification of proteins that promotes productive protein folding and increases protein stability. Although N-glycosylation is important for glycoprotein folding, the precise sites of glycosylation are often not conserved between protein homologues. Here we show that, in Saccharomyces cerevisiae, proteins upregulated during sporulation under nutrient deprivation have few N-glycosylation sequons and in their place tend to contain clusters of like-charged amino-acid residues. Incorporation of such sequences complements loss of in vivo protein function in the absence of glycosylation. Targeted point mutation to create such sequence stretches at glycosylation sequons in model glycoproteins increases in vitro protein stability and activity. A dependence on glycosylation for protein stability or activity can therefore be rescued with a small number of local point mutations, providing evolutionary flexibility in the precise location of N-glycans, allowing protein expression under nutrient-limiting conditions, and improving recombinant protein production.