Biology subjects

Schwabe, J. W.

Publications and source records attributed to Schwabe, J. W..

3 recordsLinked to original sources

bioRxiv2022

Structural and biochemical insights into heterotetramer formation between human oncogenic K-Ras4BG12V and Rgl2, a RalA/B activator

About a quarter of total human cancers carry mutations in Ras isoforms. Accumulating evidence suggests that small GTPases, RalA and RalB, and their activators, Ral guanine nucleotide exchange factors (RalGEFs), play an essential role in oncogenic Ras-induced signalling. We studied the interaction between human KRas4B and the Ras association (RA) domain of Rgl2 (Rgl2RA), one of the RA-containing RalGEFs. We show that the G12V oncogenic KRas4B mutation changes the interaction kinetics with Rgl2RA. The crystal structure of the KRas4BG12V: Rgl2RA complex shows a 2:2 heterotetramer where the Switch I and Switch II regions of each KRasG12V interact with both Rgl2RA molecules. This structural arrangement is highly similar to the HRasE31K:RALGDSRA crystal structure and is distinct from the well-characterised Ras:Raf complex. Interestingly, the G12V mutation was found at the dimer interface of KRas4BG12V with its partner. Our study reveals a potentially distinct mode of Ras:effector complex formation by RalGEFs, and offers a possible mechanistic explanation for how the oncogenic KRas4BG12V hyperactivates the RalA/B pathway.

biochemistry↗

bioRxiv2022

An unexpected histone chaperone function for the MIER1 histone deacetylase complex

Histone deacetylases 1 and 2 (HDAC1/2) serve as the catalytic subunit of six distinct families of nuclear complexes. These complexes repress gene transcription through removing acetyl groups from lysine residues in histone tails. In addition to the deacetylase subunit, these complexes typically contain transcription factor and/or chromatin binding activities. The MIER:HDAC complex has hitherto been poorly characterized. Here we show that MIER1 unexpectedly co-purifies with an H2A:H2B histone dimer. We show that MIER1 is also able to bind a complete histone octamer. Intriguingly, we found that a larger MIER1:HDAC1:BAHD1:C1QBP complex additionally co-purifies with an intact nucleosome on which H3K27 is either di- or tri-methylated. Together this suggests that the MIER1 complex acts downstream of PRC2 to expand regions of repressed chromatin and to deposit histone octamer onto nucleosome-depleted regions of DNA.

biochemistry↗

bioRxiv2021

In vitro evolution predicts emerging CoV-2 mutations with high affinity for ACE2 and cross-species binding

Emerging SARS CoV-2 variants are creating major challenges in the ongoing Covid-19 pandemic. Predicting CoV-2 mutations that increase transmissibility or immune evasion would be extremely valuable in development of broad-acting therapeutics and vaccines and prioritising viral monitoring and containment. Using in vitro evolution, we identify a double mutation in CoV-2 receptor binding domain (RBD) that increases affinity for ACE2 almost 20-fold. We determine the mutant:ACE2 structure to reveal the binding mechanism and show the main affinity driver, Q498H, boosts binding of other RBD variants. We find this mutation incompatible with the common N501Y mutation, but N501Y variants can acquire Q498R to access a similar bonding network and affinity gain. We show Q498H, and Q498R plus N501Y, enable variants to bind rat ACE2 with high affinity. These mutations are now emerging in CoV-2 variants, such as the Omicron variant, where they would be expected to drive increased human-to-human and cross-species transmission.

biochemistry↗