Biology subjects

Hasan, S. M. N.

Publications and source records attributed to Hasan, S. M. N..

4 recordsLinked to original sources

bioRxiv2024

Unveiling the Structural Proteome of an Alzheimer's Disease Rat Brain Model

Studying native protein structures at near-atomic resolution in crowded environment presents a challenge. Consequently, understanding the structural intricacies of proteins within pathologically affected tissues often relies on mass spectrometry and proteomic analysis. In this study, we utilized electron cryomicroscopy (cryo-EM) and a specific method of analysis called Build and Retrieve (BaR) to investigate structural characteristics of protein complexes such as post-translational modification, active site occupancy, and arrested conformational state in Alzheimers Disease (AD) using brain lysate from a rat model (TgF344-AD) of the disease. Our findings reveal novel insights into the architecture of these complexes, which we corroborate through mass spectrometry analysis. Interestingly, it has been shown that the dysfunction of these protein complexes extends beyond AD, implicating them in cancer, as well as other neurodegenerative disorders such as Parkinsons disease, Huntingtons disease, and Schizophrenia. By elucidating the structural details of these complexes, our work not only enhances our understanding of disease pathology but also suggests new avenues for future approaches in therapeutic intervention.

biochemistry↗

bioRxiv2024

Cryo-EM of AKAP350 reveals fibrillar clusters and a potential association with DNA

Protein kinase A (PKA) is a promiscuous serine/threonine kinase that phosphorylates a broad-spectrum of effectors involved in vital processes such as glucose, glycogen, and lipid metabolism. Its activity is thus tightly controlled by a family of eukaryotic scaffolding proteins known as the A-kinase anchoring proteins (AKAPs) that confine PKA signaling to specific compartments in the cell. AKAP350 (the protein encoded by AKAP9) is a massive scaffolding protein that anchors PKA to the Golgi apparatus and the centrosome where it nucleates macromolecular signaling hubs that control microtubule nucleation and dynamics. Here, we have expressed and purified full-length AKAP350 from HEK293F cells in a functional conformation. Electron cryo-microscopy (cryo-EM) of the purified protein revealed polydisperse particles forming fibrillar clusters around 50 nm in diameter, and long, thin filaments that reconstructed into double-stranded DNA. Tomographic reconstruction of a tilt series of the purified protein by electron cryo-tomography (cryo-ET) further elucidated these fibrillar clusters as 3D bundles of entangled filaments. Mass spectrometry and DNA sequencing confirmed the co-purification of DNA and DNA binding proteins such as nuclear factor 1 B (NFIB) and nucleolin (NCL). Pulldown of NFIB and NCL, but not of CEP290, CDK5RAP2, and CEP170 was diminished in the presence of DNase-I, suggesting that AKAP350 interaction with these two proteins is mediated by DNA. Overall, this study has achieved a quality purification of AKAP350 from which a previously uncharacterized interaction landscape with DNA and DNA binding proteins was discovered.

biochemistry↗

bioRxiv2021

Polymeric assembly of endogenous Tuberous Sclerosis Protein Complex

Tuberous Sclerosis protein complex (pTSC) nucleates a proteinaceous signaling hub that integrates information about the internal and external energy status of the cell in regulation of growth and energy consumption. Biochemical and electron cryomicroscopy (cryoEM) studies of recombinant pTSC have revealed the structure and stoichiometry of the pTSC and have hinted at the possibility that the complex form large oligomers. Here, we have partially purified endogenous pTSC from fasted mammalian brains of rat and pig by leveraging a recombinant antigen binding fragment (Fab) specific for the TSC2 subunit of pTSC. We demonstrate Fab dependent purification of pTSC from membrane solubilized fractions of the brain homogenates. Negative stain electron microscopy of the samples purified from pig brain demonstrates rod-shaped protein particles with a width of 10 nm, a variable length as small as 40 nm and a high degree of conformational flexibility. Larger filaments are evident with a similar 10 nm width and up to 1 m in length in linear and web-like organizations prepared from pig brain. These observations suggest polymerization of endogenous pTSC into filamentous super-structures.

biochemistry↗

bioRxiv2019

Electron cryomicroscopy observation of acyl carrier protein translocation in type I fungal fatty acid synthase

During fatty acid biosynthesis, acyl carrier proteins (ACPs) from type I fungal fatty acid synthase (FAS) shuttle substrates and intermediates within a reaction chamber that hosts multiple spatially-fixed catalytic centers. A major challenge in understanding the mechanism of ACP-mediated substrate shuttling is experimental observation of its transient interaction landscape within the reaction chamber. Here, we have shown that ACP spatial distribution is sensitive to the presence of substrates in a catalytically inhibited state, which enables high-resolution investigation of the ACP-dependent conformational transitions within the enoyl reductase (ER) reaction site. In two fungal FASs with distinct ACP localization, the shuttling domain is targeted to the ketoacyl-synthase (KS) domain and away from other catalytic centers, such as acetyl-transferase (AT) and ER domains by steric blockage of the KS active site followed by addition of substrates. These studies strongly suggest that acylation of phosphopantetheine arm of ACP may be an integral part of the substrate shuttling mechanism in type I fungal FAS.

biophysics↗