Study of spontaneous deamidation of camel's milk α-lactalbumin

Many proteins are susceptible, both in vivo and in vitro, to non enzymatic deamidation that can lead to alterations in their structure and biological functions. Aspartyl and isoaspartyl residues are the primary products of this non-enzymatic reaction that proceeds through the succinimide pathway with a metastable cyclic imide as an intermediate. Camel's milk α-lactalbumin was purified by FPLC on ion exchange column (Mono Q) and the pure fraction of the α-lactalbumin was dialysed and freeze-dried. Purified α-lactalbumin was incubated for 80h at 37°C in deamidation buffer (150 mM phosphate buffer, pH 7.4 or 8.4). Protein concentration was 15 mg mL-1. At specific time points, 150 µL aliquots were withdrawn and the kinetics of spontaneous deamidation of the α-lactalbumin was followed by FPLC which shows the presence of two isoformes, this result was confirmed by electrophoresis analysis on Alkaline-PAGE. The pHi of the two isoformes was estimated by a two-dimensional isoelectrophoresis. To compare the rate of camel α-lactalbumin deamidation, the half-life of native α-lactalbumin was calculated at pH 7.4 and 8.4, the result shows that the deamidation of camel α-lactalbumin is faster at elevated pH.