Molecular chaperones act with folding co-chaperones to suppress protein aggregation and refold stress damaged proteins. However, it is not clear how slowly folding or misfolded polypeptides are targeted for proteasomal degradation. Generally, selection of proteins for degradation is mediated by E3 ubiquitin ligases of the mechanistically distinct HECT and RING domain sub-types. Recent studies suggest that the U-box protein family represents a third class of E3 enzymes. CHIP, a U-box-containing protein, is a degradatory co-chaperone of heat-shock protein 70 (Hsp70) and Hsp90 that facilitates the polyubiquitination of chaperone substrates. These data indicate a model for protein quality control in which the interaction of Hsp70 and Hsp90 with co-chaperones that have either folding or degradatory activity helps to determine the fate of non-native cellular proteins.

中文翻译：

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蛋白质质量控​​制：含有U-box的E3泛素连接酶参与其中。

分子伴侣与折叠的伴侣伴侣共同作用，以抑制蛋白质聚集并重新折叠应力受损的蛋白质。然而，尚不清楚折叠或错误折叠的多肽靶向蛋白酶体降解的速度如何。通常，用于降解的蛋白质的选择是由机制不同的HECT和RING域亚型的E3泛素连接酶介导的。最近的研究表明，U-box蛋白家族代表第三类E3酶。CHIP是一种包含U盒的蛋白质，是热休克蛋白70（Hsp70）和Hsp90的降解性伴侣蛋白，可促进伴侣底物的多泛素化。