Chicken egg white cystatin is a well-known member of cystatin family. It is a competitive and reversible inhibitor of papain-like cysteine proteinases.

As chicken eggs are popular nutrition products, chicken cystatin is a frequent element of diet. Thermal processing of eggs in presence of sugars may lead to non-enzymatic glycation of proteins, e.g. cystatin. Products of thermal glycation of dietary proteins, similar to advanced glycation-end products found in diabetes organisms, may result in several negative biochemical effects. The aim of our study was to perform thermal glycation of cystatin and to determine its conformational and biochemical changes.

The dry thermal method was used to conjugate D-glucose with chicken cystatin. Next the native cystatin and its glycated form were tested for proteinase inhibitory activity against papain. Experiment proved that antipapain activity of glycated protein was insignificantly lowered comparing to its non-glycated form. Immunological dot-blotting tests showed that glycated and native forms of cystatin slightly differs in their ability of binding immunoglobulins (what may be the result of some conformational changes of analysed proteins). After SDS-PAGE electrophoresis we have observed that thermal glycation process results in polymerization of protein (amyloid structures are created). PAGE electrophoresis have clearly shown the presence of di- and tetramers of cystatin. We have also examined the thermo- and pH-stability. Native cystatin is highly resistant to heating and pH changes. The non-enzymatic glycation of cystatin has improved its thermal and pH stabilities.

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