Biology subjects

Absmeier, E.

Publications and source records attributed to Absmeier, E..

6 recordsLinked to original sources

bioRxiv2024

Molecular insights into dynamic protein structures by high-contrast crosslinking mass spectrometry

Proteins are comprised of structured domains and dynamic regions, and both are essential for biological function. However, studying dynamic regions is challenging using most structural biology methods, including crosslinking mass spectrometry. Here, we dramatically improve the usefulness of distance restraints from crosslinking MS by taking advantage of short-lived reactive species generated from diazirine-based photo-crosslinking. This leads to a clear view of complex topologies and conformational changes, including in dynamic regions. We demonstrate that photo-crosslinking MS data can be used to model flexible regions and conformational changes in the DNA repair complexes; Fanconi Anemia core complex and FANCD2-FANCI. In addition, we obtain new insights into the architecture and arrangement of the highly flexible CCR4-NOT mRNA deadenylation complex. The improved contrast of photo-crosslinking empowers structural biology by providing clearer structural insights into dynamic biological systems that have eluded other structural biology approaches.

molecular biology↗

bioRxiv2023

Mechanism of ribosome-associated mRNA degradation during tubulin autoregulation

SUMMARYMicrotubules play crucial roles in cellular architecture, intracellular transport, and mitosis. The availability of free tubulin subunits impacts polymerization dynamics and microtubule function. When cells sense excess free tubulin, they trigger degradation of the encoding mRNAs, which requires recognition of the nascent polypeptide by the tubulin-specific ribosome-binding factor TTC5. How TTC5 initiates decay of tubulin mRNAs is unknown. Here, our biochemical and structural analysis reveals that TTC5 recruits the poorly studied protein SCAPER to the ribosome. SCAPER in turn engages the CCR4-NOT deadenylase complex through its CNOT11 subunit to trigger tubulin mRNA decay. SCAPER mutants that cause intellectual disability and retinitis pigmentosa in humans are impaired in CCR4-NOT recruitment, tubulin mRNA degradation, and microtubule-dependent chromosome segregation. Our findings demonstrate how recognition of a nascent polypeptide on the ribosome is physically linked to mRNA decay factors via a relay of protein-protein interactions, providing a paradigm for specificity in cytoplasmic gene regulation.

molecular biology↗

bioRxiv2022

Specific recognition and ubiquitination of slow-moving ribosomes by human CCR4-NOT

Eukaryotic messenger RNA (mRNA) decay is generally initiated by removal of the 3 polyadenosine (poly(A)) tail by the CCR4-NOT complex. Yeast Ccr4-Not binds and ubiquitinates ribosomes stalled on mRNAs with sub-optimal codons to trigger deadenylation and decay of the associated transcript. However, the mammalian ortholog of the E3 ubiquitin ligase subunit, CNOT4, is not a constitutive component of human CCR4-NOT. It therefore remains unclear how the mammalian deadenylation machinery targets stalled ribosomes. Here, we reconstitute translational stalling on non-optimal codons. We find that human CCR4-NOT recognizes translating mammalian ribosomes and is required for stable CNOT4 association. Our cryoEM structure reveals that the CNOT3 subunit detects slow translation and locks the L1 stalk of the ribosome in an open conformation to impede further elongation. Using crosslinking mass spectrometry, we show that CNOT4 and CNOT11 also bind in the vicinity of the E site. Overall, our work defines how CCR4-NOT enforces ribosomal stalling in response to low codon optimality.

molecular biology↗

bioRxiv2021

Long-range allosteric effects - How adenine nucleotides shape the conformational landscape of the Ski2-like RNA helicase, Brr2

Brr2 is an essential Ski2-like RNA helicase that exhibits a unique structure among the spliceosomal helicases. Brr2 harbors a catalytically active N-terminal helicase cassette and a structurally similar, but enzymatically inactive C-terminal helicase cassette. Both cassettes contain a nucleotide binding pocket. Here we use biophysical and computational methods to delineate the functional connectivity between the cassettes and how occupancy of the nucleotide binding sites may influence each other. Our results show that Brr2 exhibits high specificity for adenine nucleotides with both cassettes binding ADP tighter than ATP. Adenine nucleotide affinity for the inactive C-terminal cassette is more than two orders of magnitude higher than that of the active N-terminal cassette, largely determined by slow nucleotide release. Mutations at the inter-cassette surfaces and in the connecting linker diminish the affinity of adenine nucleotides for both cassettes. Abrogation of nucleotide binding at the C-terminal cassette reduces nucleotide binding at the N-terminal cassette, 70 [A] away. Molecular dynamics simulations identified structural communication lines that likely mediate the long-range allosteric effects. Together, our results reveal intricate networks of intra-molecular interactions in the complex Brr2 RNA helicase, which fine-tune its nucleotide affinities and which could be exploited for regulating the enzyme during splicing.

biochemistry↗

bioRxiv2020

The interaction of DNA repair factors ASCC2 and ASCC3 is affected by somatic cancer mutations

The ASCC3 subunit of the activating signal co-integrator complex is a dual-cassette Ski2-like nucleic acid helicase that provides single-stranded DNA for alkylation damage repair by the -ketoglutarate-dependent dioxygenase, AlkBH3. Other ASCC components integrate ASCC3/AlkBH3 into a complex DNA repair pathway. We mapped and structurally analyzed interacting ASCC2 and ASCC3 regions. The ASCC3 fragment comprises a central helical domain and terminal, extended arms that clasp the compact ASCC2 unit. ASCC2-ASCC3 interfaces are evolutionarily highly conserved and comprise a large number of residues affected by somatic cancer mutations. We quantified contributions of protein regions to the ASCC2-ASCC3 interaction, observing that changes found in cancers lead to reduced ASCC2-ASCC3 affinity. Functional dissection of ASCC3 revealed similar organization and regulation as in the spliceosomal RNA helicase, Brr2. Our results delineate functional regions in an important DNA repair complex and suggest possible molecular disease principles.

biochemistry↗

bioRxiv2019

Molecular Mechanism Underlying Inhibition of Intrinsic ATPase Activity in a Ski2-like RNA Helicase

RNA-dependent NTPases can act as RNA/RNA-protein remodeling enzymes and typically exhibit low NTPase activity in the absence of RNA/RNA-protein substrates. How futile intrinsic NTP hydrolysis is prevented is frequently not known. The ATPase/RNA helicase Brr2 belongs to the Ski2-like family of nucleic acid-dependent NTPases and is an integral component of the spliceosome. Comprehensive nucleotide binding and hydrolysis studies are not available for a member of the Ski2-like family. We present crystal structures of Chaetomium thermophilum Brr2 in the apo, ADP-bound and ATPyS-bound states, revealing nucleotide-induced conformational changes and a hitherto unknown ATPyS binding mode. Our results in conjunction with Brr2 structures in other molecular contexts reveal multiple molecular mechanisms that contribute to the inhibition of intrinsic ATPase activity, including an N-terminal region that restrains the RecA-like domains in an open conformation and exclusion of an attacking water molecule, and suggest how RNA substrate binding can lead to ATPase stimulation.\n\nHIGHLIGHTSO_LICrystal structures of Brr2 in complex with different adenine nucleotides.\nC_LIO_LIThe Brr2 N-terminal region counteracts conformational changes induced by ATP binding.\nC_LIO_LIBrr2 excludes an attacking water molecule in the absence of substrate RNA.\nC_LIO_LIDifferent helicase families resort to different NTPase mechanisms.\nC_LI

biochemistry↗