Cloning, Purification and Characterization of the Caenorhabditis Elegans Small Glutamine-rich Tetratricopeptide Repeat-containing Protein

We have cloned and expressed the putative Caenorhabditis elegans orthologue for small glutamine-rich tetratricopeptide repeat-containing protein, now assigned the gene name sgt-1 in the C. elegans genome database. Characterization of the purified protein by cross-linking, mass spectrometry and gel filtration experiments provides unambiguous evidence that SGT-1 forms homo-dimers in solution. The hydrodynamic dimensions of SGT-1 dimers in relation to their molecular weight suggest a protein with a low level of compactness and an extended conformation. Human SGT has been shown to interact with and regulate the activity of heat shock proteins Hsp70 and Hsp90 via a TPR domain mediated interaction. The SGT TPR domain (SGT-1-TPR, residues 100-226) was cloned, purified and shown by ITC and CD analysis to interact with the C-terminal peptides of Hsp70 and Hsp90 with comparable affinities although there is no evidence of a recently proposed coupled binding-folding mechanism for TPR domains.