Kwon Ae-Ran, Trame Christine B, McKay David B
Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
J Struct Biol. 2004 Apr-May;146(1-2):141-7. doi: 10.1016/j.jsb.2003.11.003.
The HslUV protease-chaperone complex degrades specific protein substrates in an ATP-dependent reaction. Current models propose that the HslU chaperone, a AAA protein of the Clp/Hsp100 family, binds and unfolds substrates and translocates the polypeptide into the catalytic cavity of the HslV protease. These processes are being characterized using substrates that are targeted to HslUV with a carboxy-terminal fusion of the natural substrate SulA or the carboxy-terminal 11 amino acid residues thereof. In a tandem fusion of green fluorescent protein with SulA, HslUV degrades the SulA moiety but not green fluorescent protein. Wild type and mutant Arc repressor variants are degraded; over a range of substrate stabilities, the specific rate of degradation and its dependence on substrate stability is similar to that of ClpXP. For a hyperstable Arc variant having an intermolecular disulfide bond, the rate of degradation by HslUV is an order of magnitude slower than by ClpXP. Similarity in degradation rates for a subset of substrates by HslUV and ClpXP suggests a similarity in mechanism of the apparent rate-limiting steps of unfolding and translocation by the chaperone components HslU and ClpX. The fall-off in degradation by HslUV for the more stable substrates that are degraded by ClpXP is consistent with the two systems acting on different spectra of biological substrates.
HslUV蛋白酶伴侣复合物在ATP依赖的反应中降解特定的蛋白质底物。目前的模型认为，HslU伴侣蛋白是Clp/Hsp100家族的一种AAA蛋白，它结合并展开底物，然后将多肽转运到HslV蛋白酶的催化腔中。这些过程是通过将天然底物SulA或其羧基末端的11个氨基酸残基与羧基末端融合，从而将底物靶向HslUV来进行表征的。在绿色荧光蛋白与SulA的串联融合中，HslUV降解SulA部分，但不降解绿色荧光蛋白。野生型和突变型Arc阻遏物变体被降解；在一系列底物稳定性范围内，降解的特定速率及其对底物稳定性的依赖性与ClpXP相似。对于具有分子间二硫键的超稳定Arc变体，HslUV的降解速率比ClpXP慢一个数量级。HslUV和ClpXP对一部分底物的降解速率相似，这表明伴侣蛋白组分HslU和ClpX在展开和转运的表观限速步骤机制上具有相似性。对于ClpXP能够降解的更稳定底物，HslUV的降解能力下降，这与这两个系统作用于不同生物底物谱的情况一致。
