Effects of macromolecular crowding on the structural stability of human α-lactalbumin

• Published in: Acta biochimica et biophysica Sinica 2012-08, Vol.44 (8), p.703-711
• Main Authors: Zhang, De-Lin, Wu, Ling-Jia, Chen, Jie, Liang, Yi
• Format: Article
• Language: English
• Subjects: Calcium - chemistry; Calorimetry - methods; Circular Dichroism; Humans; Lactalbumin - chemistry; Macromolecular Substances; Molecular Conformation; Polyethylene Glycols - chemistry; Protein Conformation; Protein Denaturation; Protein Folding; Proteins - chemistry; Spectrometry, Fluorescence - methods; Thermodynamics; Trypsin - chemistry; 乳清蛋白; 人体结构; 右旋糖酐; 大分子拥挤; 排除体积效应; 热稳定性; 相互作用; 非特异性
• ISSN: 1672-9145; 1745-7270
• DOI: 10.1093/abbs/gms052

The folding of protein, an important process for protein to fulfill normal functions, takes place in crowded physiological environments, α-Lactalbumin, as a model system for proteinolding studies, has been used extensively because it can form stable molten globule states under a range of conditions. Here we report that the crowding agents Ficoll 70, dextran 70, and polyethylene glycol （PEG） 2000 have different effects on the structural stability of human α-lactalbumin （HLA） represented by the transition to a molten globule state： dextran 70 dramatically enhances the thermal stability of Ca^2＋-depleted HLA （apo-HLA） and Ficoll 70 enhances the thermal stability of apo-HLA to some extent, while PEG 2000 significantly decreases the thermal stability of apo-HLA. Ficoll 70 and dextran 70 have no obvious effects on trypsin degradation of apo-HLA but PEG 2000 accelerates apo-HLA degrad- ation by trypsin and destabilizes the native conformation of apo-HLA. Furthermore, no interaction is observed between apo-HLA and Ficoll 70 or dextran 70, but a weak, non-specific interaction between the apo form of the protein and PEG 2000 is detected, and such a weak, non-specific interaction could overcome the excluded- volume effect of PEG 2000. Our data are consistent with the results of protein stability studies in cells and suggest that stabilizing excluded-volume effects of crowding agents can be ameliorated by non-specific interactions between proteins and crowders.