Central domain deletions affect the SAXS solution structure and function of Yeast Hsp40 proteins Sis1 and Ydj1

To investigate the relevance of central domains on the structure and function of Ydj1 and Sis1 we prepared Sis1 constructs deleting specific domains. The mutants had decreased affinity for heated luciferase but were equally capable of stimulating ATPase activity of Hsp70. Detailed low resolution structures were obtained and the overall flexibility of Hsp40 and its mutants were assessed using SAXS methods. Deletion of either the G/M or the G/M plus CTDI domains had little impact on the quaternary structure of Sis1 analyzed by the SAXS technique. However, deletion of the ZFLR-CTDI changed the relative position of the J-domains in Ydj1 in such a way that they ended up resembling that of Sis1. The results revealed that the G/F and G/M regions are not the only flexible domains. All model structures exhibit a common clamp-like conformation.Our results suggest that the central domains, previously appointed as important features for substrate binding, are also relevant keeping the J-domains in their specific relative positions. The clamp-like architecture observed seems also to be favorable to the interactions of Hsp40 with Hsp70.Molecular chaperones are proteins that are involved in assisting the folding and assembly of newly synthesized proteins recognizing non-native substrate proteins predominantly via their exposed hydrophobic residues [1]. However, the conditions for the successful folding in vivo are not always favorable. The cellular environment is crowded and thus protein denaturation and aggregation will be major problems. Thus, there is the need for chaperones that also protect cells from elevated temperature or other cellular stress situations, to achieve successful folding of proteins in vivo. There are several families of Heat Shock Proteins (HSPs), each family acts to assist protein folding in a different way.An important chaperone family is the 40-kDa Heat shock protein (Hsp40). Chaperones from the Hsp40/DnaJ family play important roles in cells by working t