Biology subjects

Gierasch, L. M.

Publications and source records attributed to Gierasch, L. M..

3 recordsLinked to original sources

bioRxiv2025

The nucleotide exchange factor, GrpE, modulates substrate affinity by interaction of its N-terminal tails with the DnaK substrate-binding domain.

The 70-kDa heat shock proteins (Hsp70s) assist in protein folding through allosteric communication between their nucleotide-binding domains (NBDs) and substrate-binding domains (SBDs), which are connected by an interdomain linker. Their nucleotide-dependent allosteric cycle is modulated by ligand binding and co-chaperones, including nucleotide exchange factors (NEFs). GrpE, the NEF for the E. coli Hsp70, DnaK, has been proposed to have a dual effect on the chaperone, facilitating the exchange of ADP for ATP in the NBD in a temperature-dependent fashion and promoting substrate release from the SBD. We recently reported NMR-based evidence that GrpE binding to DnaK has a direct structural effect on the SBD. Here, we expanded on these findings and obtained new evidence for a model in which the disordered N-terminal tails of GrpE facilitate peptide dissociation from the nucleotide-free DnaK/GrpE complex by transiently binding to the canonical substrate-binding site in the SBD. This GrpE/SBD interaction, while weak, is favored by the high local concentration of the tails around the SBD after complex formation. Moreover, we identified the DnaK binding motif in GrpEs N-terminal disordered tails as 17IIM19, which is conserved across many bacterial species. Excitingly, our data further suggest a mechanism for the temperature-dependence of GrpEs modulation of DnaKs refolding activity: as the temperature increases, unfolding of GrpEs coiled-coil weakens its contacts with the SBD, reducing N-terminal tail binding, and thus increasing DnaK affinity to substrates.

biochemistry↗

bioRxiv2025

The cysteine-rich domain of SEP15, a selenoprotein co-chaperone of the ER chaperone, UDP-glucose:glycoprotein glucosyltransferase, adopts a novel fold

Proteins targeted to the secretory pathway are involved in a myriad of biological processes but can only do so when properly folded. Within the endoplasmic reticulum, glycoprotein folding is regulated by the enzyme UDP-glucose:glycoprotein glucosyltransferase (UGGT) and its oxidoreductase partner, the 15-kDa selenoprotein (SEP15 aka SELENOF). The interaction between these two chaperones is poorly understood, limiting understanding of their function. SEP15 is comprised of two domains, a C-terminal thioredoxin-like domain, the structure of which has been reported (PDB 2A4H), and an approximately 50-residue long N-terminal cysteine-rich domain (CRD), of unknown structure. Here, we use a combination of AlphaFold structural predictions and NMR spectroscopy to elucidate the structure of the SEP15 CRD, which mediates the interaction with UGGT. These data reveal that this domain forms a previously undescribed helical fold stabilized by three disulfide bonds between residues C10-C42, C21-C43, and C24-C39. Furthermore, our results validate our reported model of the UGGT/SEP15 complex and lay the foundation for future studies of its interaction with glycoprotein substrates.

biochemistry↗

bioRxiv2023

The conformational landscape of a serpin N-terminal subdomain facilitates folding and in-cell quality control

Many multi-domain proteins including the serpin family of serine protease inhibitors contain non-sequential domains composed of regions that are far apart in sequence. Because proteins are translated vectorially from N-to C-terminus, such domains pose a particular challenge: how to balance the conformational lability necessary to form productive interactions between early and late translated regions while avoiding aggregation. This balance is mediated by the protein sequence properties and the interactions of the folding protein with the cellular quality control machinery. For serpins, particularly 1-antitrypsin (AAT), mutations often lead to polymer accumulation in cells and consequent disease suggesting that the lability/aggregation balance is especially precarious. Therefore, we investigated the properties of progressively longer AAT N-terminal fragments in solution and in cells. The N-terminal subdomain, residues 1-190 (AAT190), is monomeric in solution and efficiently degraded in cells. More y-rich fragments, 1-290 and 1-323, form small oligomers in solution, but are still efficiently degraded, and even the polymerization promoting Siiyama (S53F) mutation did not significantly affect fragment degradation. In vitro, the AAT190 region is among the last regions incorporated into the final structure. Hydrogen-deuterium exchange mass spectrometry and enhanced sampling molecular dynamics simulations show that AAT190 has a broad, dynamic conformational ensemble that helps protect one particularly aggregation prone y-strand from solvent. These AAT190 dynamics result in transient exposure of sequences that are buried in folded, full-length AAT, which may provide important recognition sites for the cellular quality control machinery and facilitate degradation and, under favorable conditions, reduce the likelihood of polymerization.

biophysics↗