Small glutamine-rich tetratricopeptide repeat-containing protein is composed of three structural units with distinct functions.

Previously, we identified the human small glutamine-rich tetratricopeptide repeat-containing protein (SGT) as a co-chaperone. The tetratricopeptide repeat (TPR) domain in SGT is responsible for interacting with Hsc70. In this study, we demonstrated that the TPR domain of SGT also interacted with Hsp90. Moreover, we investigated the functional significance of regions of SGT outside the TPR domain. Evidently, the N-terminal domain of SGT is necessary and sufficient for its self-association; and, SGT may be a dimer elongated in shape. The C-terminal glutamine-rich region has the capacity to interact with short peptide segments composed of consecutive non-polar amino acids. The C-terminal fragment of SGT indeed plays a role in the association of SGT with in vitro translated rat type 1 glucose transporter, an integral membrane protein folded in a non-physiological state. Moreover, in the presence of SGT, the degradation of the transporter in reticulocyte lysates is inhibited. Taking together, SGT can be separated into three structural units with distinct functions.