van de Klundert F A, Smulders R H, Gijsen M L, Lindner R A, Jaenicke R, Carver J A, de Jong W W
Department of Biochemistry, University of Nijmegen, The Netherlands.
Eur J Biochem. 1998 Dec 15;258(3):1014-21. doi: 10.1046/j.1432-1327.1998.2581014.x.
Hsp20 is one of the newly described members of the mammalian small heat-shock protein (sHsp) family. It occurs most abundantly in skeletal muscle and heart. We isolated clones for Hsp20 from a rat heart cDNA library, and expressed the protein in Escherichia coli to characterize this little known sHsp. Recombinant Hsp20 displayed similar far-ultraviolet circular dichroism spectra as the most closely related sHsp, alpha B-crystallin, but was less heat stable, denaturing upon heating to 50 degrees C. While other mammalian recombinant sHsps form large multimeric complexes, Hsp20 occurs in two complex sizes, 43-kDa dimers and 470-kDa multimers. The ratio between the two forms depends on protein concentration. Moreover, Hsp20 has a much lower chaperone-like activity than alpha B-crystallin, as indicated by its relatively poor capacity to diminish the reduction-induced aggregation of insulin B chains. Hsp20 is considerably shorter at the C-terminus and less polar than other sHsps, but 1H-NMR spectroscopy reveals that the last 10 residues are flexible, as in the other sHsps. Our findings suggest that Hsp20 is a special member of the sHsp family in being less heat stable and tending to form dimers. These properties, together with the shorter and less polar C-terminal extension, may contribute to the less effective chaperone-like activity.
热休克蛋白20（Hsp20）是哺乳动物小分子热休克蛋白（sHsp）家族中新近描述的成员之一。它在骨骼肌和心脏中含量最为丰富。我们从大鼠心脏cDNA文库中分离出Hsp20的克隆，并在大肠杆菌中表达该蛋白，以对这种鲜为人知的sHsp进行表征。重组Hsp20显示出与最密切相关的sHsp——αB-晶状体蛋白相似的远紫外圆二色光谱，但热稳定性较差，加热到50摄氏度时会变性。虽然其他哺乳动物重组sHsp形成大型多聚体复合物，但Hsp20以两种复合物大小存在，即43 kDa的二聚体和470 kDa的多聚体。两种形式之间的比例取决于蛋白质浓度。此外，Hsp20的伴侣样活性比αB-晶状体蛋白低得多，这表现在其减少胰岛素B链还原诱导聚集的能力相对较差。Hsp20的C末端比其他sHsp短得多且极性较小，但1H-NMR光谱显示，与其他sHsp一样，其最后10个残基是灵活的。我们的研究结果表明，Hsp20是sHsp家族中的一个特殊成员，其热稳定性较低且倾向于形成二聚体。这些特性，连同较短且极性较小的C末端延伸，可能导致其伴侣样活性较低。
