Development of an oxalate-affinity chromatographic column to isolate oxalate-binding proteins

Abstract

Calcium oxalate (CaOx) is the major crystalline component in kidney stones. Many previous studies on stone modulation have focused mainly to calcium-binding proteins, whereas oxalate-binding proteins remain under-investigated due to a lack of a simple method to purify oxalate-binding proteins. Therefore, we have developed an affinity chromatographic column to isolate or purify oxalate-binding proteins. The oxalate-affinity column developed contained EAH-Sepharose 4B beads conjugated with oxalic acid by carbodiimide reaction using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) as an activator. The coupling efficacy of coupled beads (oxalic acid-EAH Sepharose 4B) was determined by a competitive ninhydrin assay to quantify the remaining amino group on EAH-Sepharose 4B. In addition, the oxalate-affinity column showed high specific binding to a known oxalate-binding protein (p62) but not to an irrelevant protein (carbonic anhydrase). In conclusion, we have established the oxalate-affinity chromatographic column, which showed the high efficiency to isolate oxalate-binding proteins. This novel chromatographic column will be very useful for future stone research, particularly in the area of stone modulation by oxalate-binding proteins.