Efficient expression of SRK intracellular domain by a modeling-based protein engineering

•Stable expression of SRK kinase domain in E. coli by modeling-based protein engineering.•Engineered SRK protein retains kinase activity.•The yield of engineered SRK expressed in E. coli is 7.6 mg/L.

S-locus protein kinase (SRK) is a receptor kinase that plays a critical role in self-recognition in the Brassicaceae self-incompatibility (SI) response. SRK is activated by binding of its ligand S-locus protein 11 (SP11) and subsequently induced phosphorylation of the intracellular kinase domain. However, a detailed activation mechanism of SRK is still largely unknown because of the difficulty in stably expressing SRK recombinant proteins. Here, we performed modeling-based protein engineering of the SRK kinase domain for stable expression in Escherichia coli. The engineered SRK intracellular domain was expressed about 54-fold higher production than wild type SRK, without loss of the kinase activity, suggesting it could be useful for further biochemical and structural studies.