Biology subjects

Kaplan-Ashiri, I.

Publications and source records attributed to Kaplan-Ashiri, I..

3 recordsLinked to original sources

bioRxiv2024

Controlled pH Alteration Enables Guanine Accumulation and Drives Crystallization within Iridosomes

Many animals exhibit remarkable colors produced by the constructive interference of light reflected from arrays of intracellular guanine crystals. These systems are utilized for various purposes, including vision, camouflage, communication, and thermal regulation. Each guanine crystal forms within a membrane-bound organelle called an iridosome, where precise control over crystal formation occurs. While the presence of guanine crystals in iridosomes is well-documented, the mechanisms facilitating the accumulation of water-insoluble guanine and driving its crystallization remain unclear. Here, we employ advanced imaging and spectroscopy techniques to characterize the maturation of iridosomes in zebrafish iridophores during development. Using cryo-electron microscopy, we found that amorphous guanine accumulates in early-stage iridosomes. Synchrotron-based soft X-ray microscopy studies revealed that, unlike mature crystals, the accumulated guanine is initially in its protonated state. Live imaging with a pH sensor demonstrated that early-stage iridosomes are acidic and that their pH gradually approaches neutrality during maturation. Additionally, the application of a V-ATPase inhibitor reduced the acidity of iridosomes and significantly decreased crystal formation, suggesting the involvement of V-ATPase in regulating the organelle pH. Our findings reveal new insights into the molecular mechanisms facilitating guanine accumulation and crystallization within iridosomes, emphasizing the pivotal role of pH alternations in the precise formation of biogenic crystals.

cell biology↗

bioRxiv2023

Cell-mediated cholesterol crystal processing and clearance observed by 3D cryo-imaging in human atherosclerotic plaques

Atherosclerosis is a pathology affecting the arteries, characterized by the buildup of plaques in the blood vessel walls. Atherosclerosis is the main cause of cardiovascular diseases, which constitute the leading cause of death in the world. Cholesterol crystals are the main components of the plaques, which actively participate in plaque growth and rupture and do not dissolve in aqueous environments. Employing novel cryo-scanning electron microscopy techniques, we examined human atherosclerotic plaques at high resolution, in 3D, and in close to native conditions. We show that cholesterol crystal clearance occurs in advanced human plaques through the activity of cells. We suggest that this occurs by enzymatic esterification of cholesterol to cholesteryl ester, which aggregates into intra- and extra-cellular pools. This discovery provides further understanding of the disease process in atherosclerosis, and may inspire new therapeutic approaches.

pathology↗

bioRxiv2023

Metal Ions Guide the Production of Silkworm Fibers

Silk fibers unique mechanical properties have made them a desirable material for various applications, from medical to optical materials and even in sensing. Yet, to date, no synthetic method has come close to reproducing this remarkably strong biomaterial due to the complexity and insufficient understanding of the mechanism of silk fiber formation. While ions are known to play a key role in the production of natural silk fiber, how they do so has thus far eluded discovery. Here we report that a broad composition of metal ions guides structural transformations in the silk fibroin protein inside the silkworm silk gland. By using a combination of cryo-electron microscopy techniques coupled with elemental analysis, we followed the changes in the composition and spatial localization of metal ions inside the silk gland. We observed that ions are homogenously dispersed during the initial stages of silk secretion and storage inside the silk gland, but once the fibers are spun, the ions delocalize from the silk fibroin fiber core to the sericin coating gum layer. This shift in ion localization is accompanied by the alignment of protein chains and an increase in silk feedstock viscosity inside the silk gland - changes that make the protein more sensitive to shear and enable the initiation of the liquid-to-solid transition in the silk. Moreover, the selective doping of the spun silk fibers with metal ions modifies their mechanical performance. These findings highlight the importance and the dynamic role of metal ions in the evolution of silk fibers mechanical properties, enhance our understanding of the mechanism of silk fiber formation, and lay the foundations for developing new concepts in biomaterial design.

biochemistry↗