Assay of hemoglobin A_1c using lectin from Aleuria aurantia

Hemoglobin A_1c (HbA_1c) has an N-terminal fructosyl valine on the β-chain, and this modification is caused by the non-enzymatic glycosylation of hemoglobin (Hb). The relative concentration ratio of HbA_1c to total Hb is an important biomarker for the diagnosis of diabetes. HbA_1c-binding lectins were screened from 29 sources of lectin, and the lectin from Aleuria aurantia (AAL) was revealed to have higher affinity to HbA_1c than to Hb. The concentration of HbA_1c was determined by lectin-based enzyme-linked immunosorbent assay (ELISA) using the AAL lectin. Higher reproducibility of the assay was observed at 4 °C than at 25 and 37 °C. This observation is consistent with the known temperature-dependent behavior of lectins. Preincubation of HbA_1c with an anti-HbA_1c antibody inhibited the binding, suggesting that AAL binds to the N-terminal fructosyl valine epitope of HbA_1c. Higher inhibitory effect was observed for 10 mM D-fructose than for the same concentrations of L-fucose, D-fucose, or D-glucose.