Biology subjects

Lawrence, R. E.

Publications and source records attributed to Lawrence, R. E..

3 recordsLinked to original sources

bioRxiv2021

A point mutation in the nucleotide exchange factor eIF2B constitutively activates the integrated stress response by allosteric modulation

In eukaryotic cells, stressors reprogram the cellular proteome by activating the integrated stress response (ISR). In its canonical form, stress-sensing kinases phosphorylate the eukaryotic translation initiation factor eIF2 (eIF2-P), which ultimately leads to reduced levels of ternary complex required for initiation of mRNA translation. Translational control is primarily exerted through a conformational switch in eIF2s nucleotide exchange factor, eIF2B, which shifts from its active A-State conformation to its inhibited I-State conformation upon eIF2-P binding, resulting in reduced nucleotide exchange on eIF2. Here, we show functionally and structurally how a single histidine to aspartate point mutation in eIF2Bs {beta} subunit (H160D) mimics the effects of eIF2-P binding by promoting an I-State like conformation, resulting in eIF2-P independent activation of the ISR. These findings corroborate our previously proposed (Schoof et al. 2021) A/I-State model of allosteric ISR regulation.

molecular biology↗

bioRxiv2020

eIF2B Conformation and Assembly State Regulate the Integrated Stress Response

The integrated stress response (ISR) is activated by phosphorylation of the translation initiation factor eIF2 in response to various stress conditions. Phosphorylated eIF2 (eIF2-P) inhibits eIF2s nucleotide exchange factor eIF2B, a two-fold symmetric heterodecamer assembled from subcomplexes. Here, we monitor and manipulate eIF2B assembly in vitro and in vivo. In the absence of eIF2Bs -subunit, the ISR is induced because unassembled eIF2B tetramer subcomplexes accumulate in cells. Upon addition of the small-molecule ISR inhibitor ISRIB, eIF2B tetramers assemble into active octamers. Surprisingly, ISRIB inhibits the ISR even in the context of fully assembled eIF2B decamers, revealing an allosteric communication between the physically distant eIF2, eIF2-P, and ISRIB binding sites. Cryo-EM structures suggest a rocking motion in eIF2B that couples these binding sites. eIF2-P binding converts eIF2B decamers into conjoined tetramers with greatly diminished activity. Thus, ISRIBs effects in disease models could arise from eIF2B decamer stabilization, allosteric modulation, or both.

cell biology↗

bioRxiv2020

Structural mechanism for amino acid-dependent Rag GTPase switching by SLC38A9

The mechanistic target of rapamycin complex 1 (mTORC1) couples cell growth to nutrient, energy and growth factor availability (1-3). mTORC1 is activated at the lysosomal membrane when amino acids are replete via the Rag guanosine triphosphatases (GTPases) (4-6). Rags exist in two stable states, an inactive (RagA/BGDP:RagC/DGTP) and active (RagA/BGTP:RagC/DGDP) state, during low and high cellular amino acid levels (4, 5). The lysosomal folliculin (FLCN) complex (LFC) consists of the inactive Rag dimer, the pentameric scaffold Ragulator (7, 8), and the FLCN:FNIP (FLCN-interacting protein) GTPase activating protein (GAP) complex (9), and prevents activation of the Rag dimer during amino acid starvation (10, 11). How the LFC is released upon amino acid refeeding is a major outstanding question in amino-acid dependent Rag activation. Here we show that the cytoplasmic tail of the lysosomal solute carrier family 38 member 9 (SLC38A9), a known Rag activator (12-14), destabilizes the LFC. By breaking up the LFC, SLC38A9 triggers the GAP activity of FLCN:FNIP toward RagC. We present the cryo electron microscopy (cryo-EM) structures of Rags in complex with their lysosomal anchor complex Ragulator and the cytoplasmic tail of SLC38A9 in the pre and post GTP hydrolysis state of RagC, which explain how SLC38A9 destabilizes the LFC and so promotes Rag dimer activation.

biochemistry↗