Kim Dong Young, Kwon Eunju, Shin Yeon-Kyun, Kweon Dae-Hyuk, Kim Kyeong Kyu
Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Korea.
J Mol Biol. 2008 Mar 21;377(2):410-20. doi: 10.1016/j.jmb.2007.12.078. Epub 2008 Jan 11.
High-temperature requirement A (HtrA) protein has been known as a moonlighting protein that plays dual roles as a molecular chaperone and as a protease. The proteolytic activity of HtrA is switched on at elevated temperatures, whereas the chaperone function predominates at normal temperatures. The temperature-regulated functional switch of HtrA appears to be critical for the control of the stability of cellular proteins, as well as for the elimination of denatured proteins in order to maintain viability. Although certain conformational changes are expected to be concurrent with the functional activation of HtrA proteolysis, the molecular mechanisms inherent to this process have yet to be elucidated. Spin labeling electron paramagnetic resonance and fluorescence spectroscopy experiments on the HtrA from Thermotoga maritima (Tm HtrA) have shown that a helical lid (H(L)) that covers the active site is lifted up to expose the catalytic and substrate-binding sites to the solvent at elevated temperatures, whereas the overall structure is maintained over a wide temperature range. Results indicate that the proteolytic activity of Tm HtrA is turned on by the geometric change occurring around the H(L), resulting in a substrate-accessible path. In conclusion, the functional switch of Tm HtrA is embedded in the sentinel of the H(L) in terms of substrate accessibility.
高温需求A（HtrA）蛋白是一种兼职蛋白，兼具分子伴侣和蛋白酶的双重功能。HtrA的蛋白水解活性在高温时开启，而伴侣功能在常温下占主导。HtrA的温度调节功能开关对于控制细胞蛋白的稳定性以及清除变性蛋白以维持细胞活力似乎至关重要。尽管预期某些构象变化会与HtrA蛋白水解的功能激活同时发生，但这一过程的内在分子机制尚未阐明。对嗜热栖热菌HtrA（Tm HtrA）进行的自旋标记电子顺磁共振和荧光光谱实验表明，覆盖活性位点的螺旋盖（H(L)）在高温时会上抬，使催化位点和底物结合位点暴露于溶剂中，而其整体结构在较宽温度范围内保持稳定。结果表明，Tm HtrA的蛋白水解活性是由H(L)周围发生的几何变化开启的，从而形成了底物可及路径。总之，就底物可及性而言，Tm HtrA的功能开关嵌入在H(L)的“哨兵”结构中。
