Taxonomic distribution of proteins containing STI1 domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing STI1 domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

A family of ubiquitin-like proteins binds the ATPase domain of Hsp70-like Stch.

Kaye FJ, Modi S, Ivanovska I, Koonin EV, Thress K, Kubo A, Kornbluth S, Rose MD
FEBS Lett. 2000; 467: 348-55

We have isolated two human ubiquitin-like (UbL) proteins that bind to a short peptide within the ATPase domain of the Hsp70-like Stch protein. Chap1 is a duplicated homologue of the yeast Dsk2 gene that is required for transit through the G2/M phase of the cell cycle and expression of the human full-length cDNA restored viability and suppressed the G2/M arrest phenotype of dsk2Delta rad23Delta Saccharomyces cerevisiae mutants. Chap2 is a homologue for Xenopus scythe which is an essential component of reaper-induced apoptosis in egg extracts. While the N-terminal UbL domains were not essential for Stch binding, Chap1/Dsk2 contains a Sti1-like repeat sequence that is required for binding to Stch and is also conserved in the Hsp70 binding proteins, Hip and p60/Sti1/Hop. These findings extend the association between Hsp70 members and genes encoding UbL sequences and suggest a broader role for the Hsp70-like ATPase family in regulating cell cycle and cell death events.

Stress-inducible, murine protein mSTI1. Characterization of binding domains for heat shock proteins and in vitro phosphorylation by different kinases.

Lassle M, Blatch GL, Kundra V, Takatori T, Zetter BR
J Biol Chem. 1997; 272: 1876-84

We have recently isolated the cDNA for the murine homologue of the stress-inducible phosphoprotein STI1 (also known as IEF SSP 3521 or p60). STI1 was previously shown to be 2-fold up-regulated in MRC-5 fibroblasts upon viral transformation and to exist in a macromolecular complex with heat shock proteins of the HSP 70 and 90 families. By peptide-sequencing we have identified the two heat shock proteins that bind to murine STI1 (mSTI1) as HSC 70 and HSP 84/86. We describe two separate binding regions within mSTI1 for the two heat shock proteins. In the presence of cell extracts, the N-terminal region of mSTI1 binds preferentially to HSC 70, whereas the C-terminal portion of the molecule promotes the binding of HSP 84/86. Heat treatment caused a strong induction of mSTI1 message without affecting the steady-state level of the protein significantly. In addition, heat treatment led to changes in the isoform-composition of mSTI1. pp70(s6k), pp90(rsk), and mitogen-activated protein kinase-activated protein kinase 2 were tested as possible STI1 kinases in vitro using recombinant mSTI1 as a substrate: only pp90(rsk) was able to phosphorylate recombinant mSTI1. In vitro kinase assays using casein kinase II suggest serine 189 to be a likely phosphorylation site in mSTI1.

Hip, a novel cochaperone involved in the eukaryotic Hsc70/Hsp40 reaction cycle.

Hohfeld J, Minami Y, Hartl FU
Cell. 1995; 83: 589-98

The Hsc70-interacting protein Hip, a tetratricopeptide repeat protein, participates in the regulation of the eukaryotic 70 kDa heat shock cognate Hsc70. One Hip oligomer binds the ATPase domains of at least two Hsc70 molecules dependent on activation of the Hsc70 ATPase by Hsp40. While hydrolysis remains the rate-limiting step in the ATPase cycle, Hip stabilizes the ADP state of Hsc70 that has a high affinity for substrate protein. Through its own chaperone activity, Hip may contribute to the interaction of Hsc70 with various target proteins. We propose a mechanism for the regulation of eukaryotic Hsc70 that is distinct from that of bacterial Hsp70. The Hsc70/Hsp40/Hip system is apparently independent of a GrpE-like nucleotide exchange factor.