Role of AIP and its homologue the blindness-associated protein AIPL1 in regulating client protein nuclear translocation

The evolution and diversification of the Hsp90 co-chaperone system

The molecular chaperone Hsp90 is the central element of a chaperone machinery in the cytosol of eukaryotic cells that is characterized by a large number of structurally and functionally different co-chaperones that influence the core chaperone component in different ways and increase its influence on the proteome. From yeast to humans, the number of Hsp90 co-chaperones has increased from 14 to over 40, and new co-chaperones are still being discovered. While Hsp90 itself has only undergone limited changes in structure and mechanism from yeast to humans, its increased importance and contribution to different processes in humans is based on the evolution and expansion of the cohort of co-chaperones. In this review, we provide an overview of Hsp90 co-chaperones, focusing on their roles in regulating Hsp90 function and their evolution from yeast to humans.

XAP2 inhibits glucocorticoid receptor activity in mammalian cells

XAP2 is member of a protein family sharing the TPR protein interaction motif. It displays close homology to the immunophilins FKBP51 and FKBP52 that act via the Hsp90 folding machinery to regulate the glucocorticoid receptor (GR). We show that XAP2 inhibits GR by reducing its responsiveness to hormone in transcriptional activation. The effect of XAP2 on GR requires its interaction with Hsp90 through the TPR motif. The PPIase-like region turned out to be enzymatically inactive. Thus, PPIase activity is not essential for the action of XAP2 on GR, similarly to FKBP51 and FKBP52.

Genetic disorders involving molecular-chaperone genes: a perspective

Molecular chaperones are important for maintaining a functional set of proteins in all cellular compartments. Together with protein degradation machineries (e.g., the ubiquitin-proteasome system), chaperones form the core of the cellular protein-quality control mechanism. Chaperones are proteins, and as such, they can be affected by mutations. At least 15 disorders have been identified that are associated with mutations in genes encoding chaperones, or molecules with features suggesting that they function as chaperones. These chaperonopathies and a few other candidates are presented in this article. In most cases, the mechanisms by which the defective genes contribute to the observed phenotypes are still uncharacterized. However, the reported observations definitely point to the possibility that abnormal chaperones participate in pathogenesis. The available data open novel perspectives and should encourage searches for new genetic chaperonopathies, as well as further analyses of the disorders discussed in this article, including detection of new cases.