Isoxanthopterin: An Optically Functional Biogenic Crystal in the Eyes of Decapod Crustaceans

Palmer, B. A.; Hirsch, A.; Brumfeld, V.; Aflalo, E. D.; Pinkas, I.; Sagi, A.; Rozenne, S.; Oron, D.; Leiserowitz, L.; Kronik, L.; Weiner, S.; Addadi, L.

doi:10.1101/240366

bioRxiv · 10.1101/240366

Isoxanthopterin: An Optically Functional Biogenic Crystal in the Eyes of Decapod Crustaceans

Palmer, B. A.·Hirsch, A.·Brumfeld, V.·Aflalo, E. D.·Pinkas, I.·Sagi, A.·Rozenne, S.·Oron, D.·Leiserowitz, L.·Kronik, L.·Weiner, S.·Addadi, L.

View original source ↗Export metadata ↓

Abstract

The eyes of some aquatic animals form images through reflective optics. Shrimp, lobsters, crayfish and prawns possess reflecting superposition compound eyes, composed of thousands of square-faceted eye-units (ommatidia). Mirrors in the upper part of the eye (the distal mirror) reflect light collected from many ommatidia onto the underlying photosensitive elements of the retina, the rhabdoms. A second reflector, the tapetum, underlying the retina, back-scatters dispersed light onto the rhabdoms. Using microCT and cryo-SEM imaging accompanied by in situ micro-X-ray diffraction and micro-Raman spectroscopy, we investigated the hierarchical organization and materials properties of the reflective systems at high resolution and under close to physiological conditions. We show that the distal mirror consists of three or four layers of sparse plate-like nano-crystals. The tapetum is a diffuse reflector composed of hollow nanoparticles constructed from concentric lamellae of crystals. Isoxanthopterin, a pteridine analog of guanine, forms both the reflectors in the distal mirror and in the tapetum. The crystal structure of isoxanthopterin was determined from crystal structure prediction calculations and verified by comparison with experimental X-ray diffraction. The extended hydrogen bonded layers of the molecules results in an extremely high calculated refractive index in the H-bonded plane, n = 1.96, which makes isoxanthopterin crystals an ideal reflecting material. The crystal structure of isoxanthopterin, together with a detailed knowledge of the reflector superstructures, provide a rationalization of the reflective optics of the crustacean eye.\n\nSignificanceAquatic animals use reflectors in their eyes either to form images or to increase photon capture. Guanine is the most widespread molecular component of these reflectors. Here we show that crystals of isoxanthopterin, a pteridine analogue of guanine, form both the image-forming distal mirror and the intensity-enhancing tapetum reflector in the compound eyes of some decapod crustaceans. The crystal structure of isoxanthopterin was determined, providing an explanation for why these crystals are so well suited for efficient reflection. Pteridines were previously known only as pigments and our discovery raises the question of which other organic molecules may be used to form crystals with superior reflective properties either in organisms or in artificial optical devices.

Source connections

Published article ↗

Explore related subjects

bioengineering Preprint

Keep this discovery

BibTeX RIS

Palmer, B. A., Hirsch, A., Brumfeld, V., Aflalo, E. D., Pinkas, I., Sagi, A., Rozenne, S., Oron, D., Leiserowitz, L., Kronik, L., Weiner, S., Addadi, L.. 2017-12-28. Isoxanthopterin: An Optically Functional Biogenic Crystal in the Eyes of Decapod Crustaceans. https://doi.org/10.1101/240366

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Comparative study of chlorophyll measurement in Physcomitrium patens moss using a conventional microscope adapted for combined 2D+1D imaging and spectral analysis

Imaging spectroscopy often requires expensive and complex equipment. Here we show a simple procedure for attaching a standard miniature fiber spectrometer to a conventional microscope, allowing easy integration of 2D imaging with 1D high-resolution spectral measurements. This combination provides much of the benefit of a full imaging spectrometer without the large equipment investment, and we provide instructions for modifying microscopes to this setup and the present measurements of living cells that demonstrate their performance. Using this setup, we compare the quantitative measurement of chlorophyll concentration in Physcomitrium patens moss using color imaging and spectral sampling.

bioengineering↗

bioRxiv2026

De novo designed single-domain antibodies protect against lethal cobra venom neurotoxicity in vivo

Generative protein design can now rapidly produce de novo binders with high affinity and functional activity against a wide range of targets, including lethal snake venom toxins. However, so far most reported successes rely on new-to-nature scaffolds with limited therapeutic precedent. Single-domain antibodies (VHHs) offer a clinically validated alternative scaffold that can bind and neutralize long-chain -neurotoxins, which are some of the most lethal components in snake venoms. Here we compare three recently established de novo design models with VHH-design capabilities (Germinal, RFantibody, and BoltzGen) for their ability to generate VHHs against the neurotoxin -cobratoxin from the monocled cobra (Naja kaouthia). Using standardized model inputs and evaluation criteria based on AlphaFold3 interface confidence (ipTM) and RMSD self-consistency, we find that Germinal was the only method to generate designs passing stringent in silico criteria for experimental testing. We therefore performed a larger Germinal design campaign employing three different VHH frameworks and experimentally validated 46 designs in vitro. Of these, 42 expressed as soluble proteins and we identified four binding hits derived from two of the three tested frameworks. Of the four binders, two lead candidates were further characterized and demonstrated high affinity (KDs of 4.1 nM and 10.8 nM), monomeric behavior and low polyreactivity, indicating favorable biophysical and developability properties, as well as functional toxin neutralization in vitro. To assess their therapeutic potential we investigated their ability to protect against -cobratoxin toxicity in vivo. Both candidates fully protected mice after -cobratoxin challenge, with 100% survival compared to a lethal control. One candidate also retained notable neutralization capacity against whole venom of Naja kaouthia with a survival of 56%, while the other protected 22% when tested in a rescue setting. Together, we demonstrate that de novo VHH design can generate high affinity single-domain antibodies with in vivo protection against lethal cobra venom neurotoxicity, and provide practical insights into method- and framework-dependent performance.

bioengineering↗

bioRxiv2026

Simple Feedback for Complex Movement: Capturing Whole-Limb Reorganization during Single-IMU Gait Retraining

Clinical gait retraining typically relies on multi-sensor arrays and high-dimensional feedback displays, imposing setup and interpretation burdens that limit routine clinical deployment. We developed a single-IMU visual biofeedback system that delivers real-time feedback of Lower Limb Trajectory Error (LLTE), a composite kinematic error metric integrating knee position and shank angle across the stance phase. Twenty able-bodied adults walked on a treadmill under two visual biofeedback targets (flexed-knee, extended-knee) while receiving either corrected (n=10) or uncorrected (n=8) feedback, where the correction accounted for limb orientation at initial contact. LLTE and stance-phase knee kinematics adapted consistently under the flexed-knee target for both feedback groups, with feedback formulation moderating the temporal trajectory of change. Adaptation toward the extended-knee target was limited, likely because participants were already operating near terminal knee extension and because the scalar error metric provided limited directional information for correction. Ankle range of motion (ROM) changed significantly across the stance phase under both target conditions, while hip ROM did not. Multiscale multivariate sample entropy (MSMVSE) increased monotonically with time scale across all conditions, with no statistically distinguishable difference between corrected and uncorrected feedback. These results suggest that single-IMU LLTE biofeedback can modify gait mechanics and that adaptation was expressed across multiple lower-limb segments rather than through changes at a single joint.

bioengineering↗