ABSTRACT
An efficient purification of recombinant proteins often requires a high ratio of recombinant to host proteins. In plants, Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the most abundant leaf protein, thus strongly impacting purification yield. Here, we describe a simple and robust purification procedure for recombinant proteins based on a differential precipitation of RuBisCO. In this context, four Legume lectin domains of Arabidopsis thaliana which belong to receptor-like kinases and cell wall proteins were produced from Nicotiana benthamiana leaves. The recombinant proteins exhibit a unique lectin domain consisting of around 250 amino acid residues with several predicted N-glycosylation sites and a six His-tag at the N-terminus. After ammonium sulphate precipitation of total soluble proteins, depletion of RuBisCO was obtained using citrate and succinate buffers during the salting-in step: this depletion was pH-dependent and the presence of di- or tri-carboxylic acids was required. The depleted protein extracts were then subjected to two chromatographic steps which were used in the negative mode to submit a protein fraction enriched as much as possible in recombinant lectin domains to a third chromatographic step (immobilized metal-ion chromatography). Three of the Legume lectin domains were purified near to homogeneity and revealed multiple N-glycosylation isoforms, particularly those from receptor-like kinases, which were characterised using specific lectins and deglycosylation enzymes. The production and purification of recombinant lectin domains will facilitate their biochemical characterisation in the context of cell-to-cell signalling and cell wall organisation.
