Biology subjects

Al-Amoudi, A.

Publications and source records attributed to Al-Amoudi, A..

4 recordsLinked to original sources

bioRxiv2026

The Posidonia oceanica Large PSI-LHCII supercomplex reveals the molecular basis of PSI spectral diversification in higher plants

Higher plant Photosystem I (PSI) can capture low-energy photons and convert them into chemical energy through special far-red absorbing chlorophylls, the red-forms. Across higher-plant evolution, red-form spectral range has shifted to match differences in far-red availability across various habitats, despite broad conservation of the antenna system and canonical red-form architecture. Here, we report the 1.9 A cryo-EM structure of a large and blue shifted PSI light-harvesting complex I and II supercomplex (L-PSI-LHCI-LHCII) from the Mediterranean seagrass Posidonia oceanica, a marine angiosperm adapted to blue-enriched underwater light depleted in far-red wavelengths. Although the PSI core remains conserved, the antenna system was selectively remodeled through incorporation of an additional Lhca1-Lhca4 heterodimer at a previously undescribed binding site, together with pigment remodeling in the LHCI and the LHCII that enhanced blue-cyan light harvesting. Comparative structural analyses identified recurrent amino-acid sites within the far-red domains that influence red-forms geometry and whose residue composition diverges strongly among blue-shifted and red-shifted plant species. These findings establish a common structural basis underlying the spectral diversification of PSI toward contrasting light environments, accounting for both seagrass adaptation to the seawater light regime and the broad range of far-red absorption in higher plants.

plant biology↗

bioRxiv2026

In Situ Landscape of Focal Adhesions and Cytoskeletal Integration Revealed by Cryo-Electron Tomography

Focal adhesions (FAs) are dynamic hubs for mechanotransduction, linking the extracellular matrix to actin fibers, intermediate filaments, and microtubules. Using cryo-electron tomography combined with 3-dimensional segmentation and subtomogram averaging, we visualize in situ the structural architecture of the FA environment at the leading edge of human fibroblasts. Our analysis reveals a rich architectural diversity within the FA landscape, where the spatial organisation and interplay of FA protein clusters, actin, vimentin, and microtubules change from the actin bundle core to its tip and across adjacent regions. Notably, we reveal diverse arrangements and connections of vimentin filaments, supporting their multifaceted role in the control and mechanics of adhesions. Together, these findings establish a structural framework for FA maturation and cytoskeletal integration, extending classical lamellipodial adhesion models and providing mechanistic insight into how FAs coordinate force transmission during cell migration.

cell biology↗

bioRxiv2025

Cryo-EM Structure of Photosystem I from mangroves in their natural environment

Photosystem I (PSI) is a multi-subunit pigment-protein supercomplex responsible for light driven electron transport in photosynthesis. Its structural plasticity under natural environmental stress remains poorly understood. Here, we present a 2.1 [A] cryo-EM structure of the PSI-LHCI supercomplex from Avicennia marina, a halotolerant, dominant mangrove species native to the Arabian Gulf that thrives in harsh coastal environments. Unlike structures derived from laboratory grown specimens, our analysis captures PSI directly from wild-grown plant leaves, offering an in-situ snapshot of plant adaptation. The core architecture comprising twelve protein subunits and four Lhca antenna proteins coordinating 157 chlorophylls, 36 carotenoids and 24 lipids is highly conserved relative to model angiosperms yet exhibits subtle shifts in antenna core coupling and pigment organization. Red-shifted chlorophylls in Lhca3, conserved among far red adapted plants, suggest an ancestral photoprotective mechanism retained in high light, high-salinity environments. Lipid mediated stabilization at interfaces likely counteracts salinity-induced membrane fluidity changes enhancing resilience under fluctuating light and salt stress. Comparative analysis with PSI structures from other vascular plants highlights both evolutionary conservation and distinct ecological tuning of LHCI organization and cofactor binding in mangroves. These insights reveal molecular strategies enabling A. marina to maintain efficient photosynthesis under extreme conditions, offering strategies for engineering photosystems in crops.

plant biology↗

bioRxiv2025

In situ structure of bacterial 50S ribosomes at 2.98 A resolution from vitreous sections.

In situ high-resolution structure determination is limited to samples thin enough to be penetrated by the electron beam during imaging. Sample thinning involves focused ion or plasma beam milling of specimens to produce lamellae with thicknesses as low as 100-150 nm. However, surface damage caused by the milling process can extend 30-60 nm deep, restricting the usable lamella thickness. This imposes limitations on single-particle analysis of macromolecular complexes due to elevated structural noise, which cannot be avoided in situ because of the dense cellular environment. Alternative methods capable of producing thinner samples are needed to reduce background. Here, we demonstrate that high-resolution structures at side-chain level, free of orientation bias, can be obtained from vitreous sections prepared by cryo-ultramicrotomy, both in vitro and in situ. We optimized the method to produce sections as thin as [~]40 nm, free from significant surface damage. Using this approach, we determined the structure of the 50S ribosomal subunit in vitro at 2.8 [A] and in situ at 3 [A] from bacterial cells. These results lay the foundation for future in situ studies of smaller complexes using CEMOVIS, as well as for methodological advances aimed at achieving compression-free sectioning.

biochemistry↗