Biology subjects

Khan, Y. A.

Publications and source records attributed to Khan, Y. A..

9 recordsLinked to original sources

bioRxiv2026

The Structure of the Picornaviral 2C:RNA holoenzyme: Molecular Basis of RNA binding and specificity by a AAA+ protein

Picornaviruses are one of the leading agents of animal and human infectious disease with at least 8 billion infections a year and cause a range of symptoms including respiratory failure and acute flaccid myelitis1. The most conserved nonstructural protein in picornaviruses is 2C2, a member of the AAA+ family of ATPases that binds RNA, and a broad spectrum antiviral target3-5. Despite its crucial role in the viral life cycle and as a clinical target, no structure of 2C bound to RNA has been structurally determined. Here we present the first structure of 2C as a hexamer bound to single stranded RNA in its central pore; a novel AAA+ protein:substrate interaction. Using the 2C:RNA holoenzyme complex structure, we characterize the mode that this AAA+ protein employs to specifically bind single stranded RNA, and demonstrate that mutations to key residues inhibit both RNA binding and viral replication in Apthovirus and Enterovirus systems, and show that the core residues responsible for binding are broadly conserved in viruses beyond Picornaviridae. Finally, we reveal that the 2C:RNA holoenzyme complex is conformationally more similar to a protein translocase adapted to bind RNA rather than other viral DNA binding SF3 helicases, underscoring how the AAA+ core module can be adapted for a variety of biochemical substrates.

biophysics↗

bioRxiv2026

yakRNA Design: A semantic multimodal RNA composer

Like proteins, RNAs have been a target for exploitation to generate synthetic molecules that can adopt enhanced and novel functions1. High-throughput assays2, combined with meticulous biochemistry, have led to the generation of some artificial RNAs but the ability to algorithmically program RNAs with an intended function remains difficult. While generative models have revolutionized protein design3,4, RNA design remains challenging due to the dearth of 3D RNA structures. Here we present You Always Know RNA (yakRNA) Design, a frontier language model that can simultaneously reason over sequence, biological function, consensus sequence, and secondary structure to generate functional RNAs. yakRNA Design is not trained on any 3D structural information but rather co-learned over a corpus of semantically labeled sequences that we designed. yakRNA Design, without any human intervention, fine-tuning, sequence optimization, scoring or selection, zero-shot designed 17 (out of 84 total designs) synthetic RNAs that were able to efficiently induce ribosomes to change their reading frames during elongation at rates comparable to or higher than most natural sequences. One of these efficient synthetic RNAs was found to have no identity to any sequence in the known universe, demonstrating how a model with semantic understanding of RNA has rich generative capabilities.

synthetic biology↗

bioRxiv2025

OT-Fusion: Cortex-conditioned Fusion of Matched PET and MRI Images Using Optimal Transport

Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) are crucial in diagnosing various medical conditions related to brain. FDG-PET provides essential functional information by capturing synaptic transmission activity, while MRI offers anatomical details. The integration of these modalities has become increasingly valuable, especially with the advent of hybrid PET/MRI systems that enable acquisition of both images in a single session. However, a notable challenge arises due to the inherent differences in spatial resolution between PET and MRI. PET images often have lower spatial resolution, leading to metabolic signals from active regions, such as the cerebral cortex and basal ganglia, appearing diffused and extended into adjacent areas like the white matter. This diffusion can complicate the accurate localization of metabolic activity, posing difficulties in clinical assessments, particularly in neurological pathologies such as epilepsy where precise mapping is crucial. To address this issue, we propose a novel approach that effectively maps the metabolic activity observed in PET onto the cortical structures delineated in MRI. We formulate this mapping as an optimal transport problem that corresponds to finding the optimum way to transform one probability distribution into another. Our method aims to enhance the structural quality of PET images, making them more detailed and informative for clinical decisions related to neurological disorders. The experiments using paired PET and MRI images indicate that our method performs better than the state-of-the-art image fusion methods on quantitative metrics and improves image quality based on visual qualitative evaluation by an expert physician.

bioinformatics↗

bioRxiv2024

In-Situ Structure and Topography of AMPA Receptor Scaffolding Complexes Visualized by CryoET

Most synapses in the brain transmit information by the presynaptic release of vesicular glutamate, driving postsynaptic depolarization through AMPA-type glutamate receptors (AMPARs). The nanometer-scale topography of synaptic AMPARs regulates response amplitude by controlling the number of receptors activated by synaptic vesicle fusion. The mechanisms controlling AMPAR topography and their interactions with postsynaptic scaffolding proteins are unclear, as is the spatial relationship between AMPARs and synaptic vesicles. Here, we used cryo-electron tomography to map the molecular topography of AMPARs and visualize their in-situ structure. Clustered AMPARs form structured complexes with postsynaptic scaffolding proteins resolved by sub-tomogram averaging. Sub-synaptic topography mapping reveals the presence of AMPAR nanoclusters with exclusion zones beneath synaptic vesicles. Our molecular-resolution maps visualize the predominant information transfer path in the nervous system.

neuroscience↗

bioRxiv2024

Pre-fusion AAA+ remodeling of target-SNARE protein complexes enables synaptic transmission

Synaptic vesicles containing neurotransmitters fuse with the plasma membrane upon the arrival of an action potential at the active zone. Multiple proteins organize trans-SNARE complex assembly and priming, leading to fusion. One target membrane SNARE, syntaxin, forms nanodomains at the active zone, and another, SNAP-25, enters non-fusogenic complexes with it. Here, we reveal mechanistic details of AAA+ protein NSF (N-ethylmaleimide sensitive factor) and SNAP (soluble NSF attachment protein) action before fusion. We show that syntaxin clusters are conserved, that NSF colocalizes with them, and characterize SNARE populations that may exist within or near them using cryo-EM. Supercomplexes of NSF, -SNAP, and either a syntaxin tetramer or one of two binary complexes of syntaxin--SNAP-25 reveal atomic details of SNARE processing and show how sequential ATP hydrolysis drives disassembly. These results suggest a functional role for syntaxin clusters as reservoirs and a corresponding role for NSF in syntaxin liberation and SNARE protein quality control preceding fusion.

neuroscience↗

bioRxiv2024

Sec18 side-loading is essential for universal SNARE recycling across cellular contexts

SNARE proteins drive membrane fusion at different cell compartments as their core domains zipper into a parallel four-helix bundle. After fusion, these bundles are disassembled by the AAA+ protein Sec18/NSF and its adaptor Sec17/-SNAP to make them available for subsequent rounds of membrane fusion. SNARE domains are often flanked by C-terminal transmembrane or N-terminal domains. Previous structures of the NSF--SNAP-SNARE complex revealed binding to the D1 ATPase pore, posing a topological constraint as SNARE transmembrane domains would prevent complete substrate threading as suggested for other AAA+ systems. Using mass-spectrometry in yeast cells, we show N-terminal SNARE domain interactions with Sec18, exacerbating this topological issue. We present cryo-EM structures of a yeast SNARE complex, Sec18, and Sec17 in a non-hydrolyzing condition, which show SNARE Sso1 threaded through the D1 and D2 ATPase rings of Sec18, with its folded, N-terminal Habc domain interacting with the D2 ring. This domain does not unfold during Sec18/NSF activity. Cryo-EM structures under hydrolyzing conditions revealed substrate-released and substrate-free states of Sec18 with a coordinated opening in the side of the ATPase rings. Thus, Sec18/NSF operates by substrate side-loading and unloading topologically constrained SNARE substrates.

biophysics↗

bioRxiv2024

Programmed ribosomal frameshifting during PLEKHM2 mRNA decoding generates a constitutively active mediator of kinesin-1-dependent lysosome transport

Programmed ribosomal frameshifting is a process where a proportion of ribosomes change their reading frame on an mRNA1, rephasing the ribosome relative to the mRNA. While frameshifting is commonly employed by viruses2, very few phylogenetically conserved examples are known in nuclear encoded genes and some of the evidence is controversial3,4. Here we report a +1 frameshifting event during decoding of the human gene PLEKHM25. This frameshifting occurs at the sequence UCC_UUU_CGG, which is conserved in vertebrates and is similar to an influenza virus sequence that frameshifts with similar efficiency6,7. The new C-terminal domain generated by this frameshift forms an -helix, which relieves PLEKHM2 from autoinhibition and allows it to move to the tips of cells via association with kinesin-1 without requiring activation by ARL8. Reintroducing both the canonically-translated and frameshifted protein are necessary to restore normal contractile function of PLEKHM2-knockout cardiomyocytes, demonstrating the necessity of frameshifting for normal cardiac activity.

molecular biology↗

bioRxiv2024

Simulating 500 million years of evolution with a language model

More than three billion years of evolution have produced an image of biology encoded into the space of natural proteins. Here we show that language models trained on tokens generated by evolution can act as evolutionary simulators to generate functional proteins that are far away from known proteins. We present ESM3, a frontier multimodal generative language model that reasons over the sequence, structure, and function of proteins. ESM3 can follow complex prompts combining its modalities and is highly responsive to biological alignment. We have prompted ESM3 to generate fluorescent proteins with a chain of thought. Among the generations that we synthesized, we found a bright fluorescent protein at far distance (58% identity) from known fluorescent proteins. Similarly distant natural fluorescent proteins are separated by over five hundred million years of evolution.

synthetic biology↗

bioRxiv2019

Contesting the evidence for -1 frameshifting in immune-functioning C-C chemokine receptor 5 (CCR5) - the HIV-1 co-receptor

During the decoding of a subset of mRNAs a proportion of ribosomes productively shift to the -1 reading frame at a specific, slippage-prone site1. While the great majority of occurrences of the \"Programmed -1 Ribosomal Frameshifting\" (-1 PRF) involve viruses2, other mobile elements or retroelements1, a dramatic instance of utilized human cellular -1 frameshifting in a non-retroelement derived mRNA has been reported. The mRNA for which -1 frameshifting was claimed due to a stimulatory pseudoknot is that which encodes immune functioning C-C chemokine receptor 5 (CCR5), the HIV-1 co-receptor3. The publication ascribed the importance of the reporter CCR5 mRNA frameshifting directing translating ribosomes to a premature termination codon leading to mRNA destabilization via the nonsense-mediated decay pathway (NMD), rather than creating a C- ...

molecular biology↗