Protein Shell Research Articles

Attachment of Virus to Host Cell Surface upon Specific Binding to Membrane Receptors and Attachment Factors

Viruses are spherical particles of size 50–500 nm. The genome (DNA or RNA) of viruses is typically encapsulated by a protein shell, known as, capsid which is further coated by a protein-rich lipid bilayer for enveloped viruses. Most non-enveloped viruses have a rigid capsid with a high structural symmetry such as icosahedral, helical, and complex. The capsid and envelope proteins are part of the structural proteins of viruses and provide distinct structural features. A major function of these structural proteins is determining the binding of viruses to host cells and these structural proteins are the most exposed on the viral surface. While viruses are simple biological nanoparticles devoid of genetic machinery, they can replicate once they enter a host cell. This is a multistep process starting with the interaction of the viral surface proteins with specific molecules of a cell surface. It is well established that virus particles must evade or cross through the 1.5-μm-thick proteoglycan shield surrounding a cell to reach the plasma membrane of the cell. Viruses have evolved to interact with the proteoglycans and receptors of the plasma membrane to trigger signals for endocytosis or membrane fusion, processes essential for cellular entry (Figure 1). Despite the fact that viruses can intrude multiple tissues and organs of a host, the infection predominates in specific organs and cell types. This is determined by the specific interaction of the viral surface proteins with the proteoglycans and plasma membrane receptors.

Reconstituted Super Paramagnetic Protein "Magnetotransferrin" for Brain Targeting to Attenuate Parkinsonism.

Transferrin is an iron transporting protein consisting of bilobal protein shells (apotransferrin) with dual domains in each lobe, holding an interdomain iron binding cleft. This cleft is useful in synthesizing an iron oxide core inside the transferrin shell. In vitro reconstitution chemistry provides a nano-dimensional synthesis of the mineral core inside the protein shell. The present study demonstrates the synthesis of magnetotransferrin with reconstitution of apotransferrin to form iron oxide nanoparticles within the transferrin. Transmission electron microscopy investigations along with analysis of electronic diffraction patterns and magnetometry studies indicate entrapment of superparamagnetic iron (III) oxide nanoparticles. In vivo/ex vivo imaging of the brain and immunogold staining of brain sections further validate the brain targeting potential of "magnetotransferrin". The in vivo therapeutic potential of magneto transferrin has been demonstrated by induction of TRPV1 magnetic stimuli protein, having an important regulatory role in Parkinsonism management. In an exploration of neuroprotective mechanisms, deacetylation of H3K27 of synuclein has been revealed through the TRPV1-mediated HDAC3 activation in the treatment of Parkinsonism. Thus, this magnetic protein could be a potent candidate for brain targeting, bio-imaging, and therapy of neurological infirmities.

In Vitro Analysis of Bacterial Microcompartments and Shell Protein Superstructures by Confocal Microscopy.

The shell proteins that comprise bacterial microcompartments (BMCs) can self-assemble into an array of superstructures such as nanotubes, flat sheets, and icosahedra. The physical characterization of BMCs and these superstructures typically relies on electron microscopy, which decouples samples from their solution context. We hypothesize that an investigation of fluorescently tagged BMCs and shell protein superstructures in vitro using high-resolution confocal microscopy will lead to new insights into the solution behavior of these entities. We find that confocal imaging is able to capture nanotubes and sheets previously reported by transmission electron microscopy (TEM). Using a combination of fluorescent tags, we present qualitative evidence that these structures intermix with one another in a hetero- and homotypic fashion. Complete BMCs are also able to accomplish intermixing as evidenced by colocalization data. Finally, a simple colocalization experiment suggests that fluorescently modified encapsulation peptides (EPs) may prefer certain shell protein binding partners. Together, these data demonstrate that high-resolution confocal microscopy is a powerful tool for investigating microcompartment-related structures in vitro, particularly for colocalization analyses. These results also support the notion that BMCs may intermix protein components, presumably from the outer shell. IMPORTANCE Microcompartments are large, organelle-like structures that help bacteria catabolize targeted metabolites while also protecting the cytosol against highly reactive metabolic intermediates. Their protein shell self-assembles into a polyhedral structure of approximately 100 to 200 nm in diameter. Inside the shell are thousands of copies of cargo enzymes, which are responsible for a specific metabolic pathway. While different approaches have revealed high-resolution structures of individual microcompartment proteins, it is less clear how these factors self-assemble to form the full native structure. In this study, we show that laser scanning confocal microscopy can be used to study microcompartment proteins. We find that this approach allows researchers to investigate the interactions and potential exchange of shell protein subunits in solution. From this, we conclude that confocal microscopy offers advantages for studying the in vitro structures of other microcompartments as well as carboxysomes and other bacterial organelles.

Determining the structural origin of quantum behaviors in fluorescent proteins.

Under physiological conditions fluorescent proteins (FP) in close proximity unexpectedly exhibit photophysical effects that are consistent with excitonic coupling: (1) ultrafast drop in anisotropy, (2) Davydov splitting in its CD spectra and (3) multiple FPs behaving as a single quantum emitter in photon antibunching experiments. We hypothesize that the FP β-barrel structure protects its internal chromophore from environmental decoherence, and thus slows its dephasing time relative to its energy transfer rate. To test this idea, we follow two parallel lines of investigation, one empirical and one theoretical. Experimentally, we prepare a catalog of fluorescent protein constructs that exhibit different combinations of energy transfer phenomena, namely excitonic coupling, and homo-FRET, and we characterize these using the three techniques mentioned above. The current list of FPs consists of Venus, LanYFP, Cerulean, EGFP, Tomato, and Ametrine, all of which were engineered into tandem dimer constructs and their appropriate monomeric controls. The variety of structurally related FP constructs should allow us to parse the origin of excitonic coupling, whether in the specific local structure along the β-barrel or the chromophore. In parallel, we employ molecular dynamics simulations to predict how the environment (the protein shell and/or solvent) impacts the excitation of the internal chromophore. We do this by estimating the total spectral density for excitation energy correlation functions as well as the contributions of composite structures to that spectral density. By applying this analysis on the various FP tandem dimer constructs, we can compare to what extent environmental coupling is predictive of observed quantum behaviors, and thus elucidate the role of structure.

Scrutinizing the protein hydration shell from MD simulations against SAXS/SANS data from a worldwide round robin benchmark.

The hydration shell of proteins plays key roles in protein stability, folding, recognition, and enzyme activity. However, it remained unclear whether the hydration shell predicted by explicit-solvent molecular dynamics (MD) simulations matches experimental conditions, while accurate experimental probes of the hydration shell structure remained limited. Small-angle scattering (SAS) in solution using X-rays (SAXS) or neutrons (SANS) in principle provides information on the hydration shell, since both the radius of gyration (Rg) and the zero-angle scattering (I0) depend on the hydration shell contrast relative to bulk solvent. Using MD simulations and explicit-solvent SAXS/SANS calculations, we computed Rg and I0 for five different proteins and a set of 18 different combinations of protein force fields and water models, and we validated the simulation results against consensus data from a recent worldwide round robin benchmark (Trewhella, Vachette et al., doi:10.1107/S2059798322009184). Overall, we find remarkable agreement between MD simulations and consensus SAS data; however the agreement is force field dependent. Certain force field/water model combinations underestimate the hydration layer contrast significantly, while water models with increased dispersion interactions may, for some proteins, overestimate the hydration layer contrast. Our study shows that explicit-solvent SAS calculation and consensus SAS data provide a novel route for scrutinizing the hydration layer of proteins.

Characterization of enzyme scaffolding inside the alpha-carboxysome by cryo-electron tomography.

Roughly 20% of bacteria employ bacterial microcompartments (BMCs) to sequester enzymatic processes. In these structures, a cargo of enzymes and accessory proteins is encased within a semi-permeable protein shell that permits passage of substrates and products but restricts movement of intermediates. In addition to their importance as a component of many bacterial species’ metabolisms, BMCs have become a target of protein engineering due to their potential for enclosing cargos of choice for alternative pharmacological and biotechnological applications. The shells can be reassembled from purified proteins, and the full operons can be functionally expressed outside their native prokaryotes.

Quantifying photosynthetic metabolites permeability across bacterial microcompartments using computational microscopy

Carboxysomes are Bacterial microcompartments, found in cyanobacteria that locally concentrate carbon dioxide (CO2) to improve the efficiency of the enzyme RuBisCO, a key step towards photosynthetic carbon fixation by the Calvin-Benson-Bassham (CBB) cycle. The carboxysome shell is made up of proteins that encapsulate RuBisCO and carbonic anhydrase. Carbonic anhydrase converts soluble bicarbonate to CO2, increasing the local concentration of CO2 for RuBisCO. In addition to CO2, other metabolites such as oxygen (O2), bicarbonate (HCO3−), 3-phosphoglyceric acid (3-PGA) and ribulose-1,5-bisphosphate (RuBP) also need to permeate through the carboxysome shell to efficiently perform CO2 fixation. Quantifying the permeability of the shell for these metabolites currently remains a challenge and one of the critical design features related to the design of synthetic bacterial microcompartments for metabolic and sustainablebioengineering applications. Leveraging a high resolution cryo-electron microscopy structure of a synthetic beta-carboxysome shell and new graphics processing unit (GPU)-resident molecular simulation engines, we determine the permeability of photosynthetic metabolites across synthetic carboxysome shell through unbiased molecular simulation at all-atom resolution. We find that the carboxysome itself is not selectively permeable to bicarbonate over carbon dioxide, as originally hypothesized. Instead, the carboxysome shell proteins form a general barrier to maintain the carbon dioxide gradient generated by carbonic anhydrase activity within the carboxysome, compensating for inefficiencies of endogenous RuBisCO, specifically slow turnover rate, and photorespiration. The results from all-atom molecular simulations presented here provide a detailed mechanistic picture, using the shell permeabilities to engineer smart synthetic bacterial microcompartments and to improve photosynthetic efficiency with a wide range of applications in sustainable, metabolic, agricultural, and biomedical engineering.

A single thiolated-phage displayed nanobody-based biosensor for label-free detection of foodborne pathogen.

Rapid and sensitive detection of bacterial pathogens present in food and environmental samples is of crucial importance to ensure human health and safety. Here, we present a one-step label-free colorimetric strategy based on M13 bacteriophage-displayed nanobody (phage-Nb) derived from camelid heavy-chain antibodies specific to Vibrio parahaemolyticus (V. parahaemolyticus). The thiolation of phage-Nb (Phage-Nb-SH) on pVIII shell proteins induces the aggregation of gold nanoparticles (AuNPs), whereas the specific interaction between nanobody and bacteria prevents the aggregation of AuNPs, resulting in visible color change due to alteration of surface plasmon resonance properties. Based on this phenomenon, a simple and sensitive colorimetric immunosensor for V. parahaemolyticus was developed. The assay can be accomplished within 100min, and exhibits a visual detection limit of 104 cfu/mL and a quantitative detection limit of 103 cfu/mL, with no cross-reactivity towards other bacterial species. This strategy takes full advantages of both the high specificity of phage-Nbs and the optical properties of AuNPs, enabling simple and rapid detection of bacterial pathogens.

Shell proteins and microstructural analysis identify the origin of shell arts with species resolution in pearl oysters

Molluscan shells are diverse, beautiful, and mechanically robust. They were commonly used by humans during ancient times as money, decorative objects, or functional tools. Luodian, a unique shell art in China dating back 3000 years, has served as a cultural carrier between China and Europe. To understand the production processes as well as underlying cultural contexts, it is important to identify the material origin of the art. This study combined proteomics and microstructural analysis to identify the raw material origins of three Luodian samples from the Qing Dynasty with species resolution and potential maturity levels. Shell proteomics and multiple sequence alignment have identified key shell matrix proteins (N66 and Pif) from Pinctada maxima, a pearl oyster distributed in the Indo-Pacific region. Although other factors (temperature, salinity, etc.) may contribute to the thickness of nacreous tablets in the shell, the thickness is inversely proportional to the shell size in the pearl oyster. We inferred the maturity of raw materials in different Luodian samples, which are tailored to different purposes. This study provides a framework and foundation for identifying the origin of various shell arts, especially those made from pearl oysters.

Производственные испытания эффективности препарата «Битоксибациллин» в Липецкой области на птицефабрике «Новоникольская»

Bitoxybacillin is a biological insecticide whose main active ingredient is bacterial spores and cells preserved in a protein shell, endotoxin and thermostable exotoxin. The results of production experiments with Bitoxybacillin held in the Lipetsk region on the Novonikolskaya poultry farm during the period from April 25 to September 10 2021 are presented in the article. According to the results of conducted researches Bitoxybacillin preparation is effective when used in 3 % concentration when the layer thickness is up to 50 cm – 3 liters per 1 m2, when manure is accumulated when the layer thickness is more than 50 cm – 10 liters per 1 m2.

In-depth magnetometry and EPR analysis of the spin structure of human-liver ferritin: from DC to 9 GHz.

Ferritin, the major iron storage protein in organisms, stores iron in the form of iron oxyhydroxide most likely involving phosphorous as a constituent, the mineral form of which is not well understood. Therefore, the question of how the ca. 2000 iron atoms in the ferritin core are magnetically coupled is still largely open. The ferritin core, with a diameter of 5-8 nm, is encapsulated in a protein shell that also catalyzes the uptake of iron and protects the core from outside interactions. Neurodegenerative disease is associated with iron imbalance, generating specific interest in the magnetic properties of ferritin. Here we present 9 GHz continuous wave EPR and a comprehensive set of magnetometry techniques including isothermal remanent magnetization (IRM) and AC susceptibility to elucidate the magnetic properties of the core of human liver ferritin. For the analysis of the magnetometry data, a new microscopic model of the ferritin-core spin structure is derived, showing that magnetic moment is generated by surface-spin canting, rather than defects. The analysis explicitly includes the distribution of magnetic parameters, such as the distribution of the magnetic moment. This microscopic model explains some of the inconsistencies resulting from previous analysis approaches. The main findings are a mean magnetic moment of 337μB with a standard deviation of 0.947μB. In contrast to previous reports, only a relatively small contribution of paramagnetic and ferrimagnetic phases is found, in the order of maximally 3%. For EPR, the over 30 mT wide signal of the ferritin core is analyzed using the model of the giant spin system [Fittipaldi et al., Phys. Chem. Chem. Phys., 2016, 18, 3591-3597]. Two components are needed minimally, and the broadening of these components suggests a broad distribution of the magnetic resonance parameters, the zero-field splitting, D, and the spin quantum number, S. We compare parameters from EPR and magnetometry and find that EPR is particularly sensitive to the surface spins of the core, revealing the potential to use EPR as a diagnostic for surface-spin disorder.

The buckling-condensation mechanism driving gas vesicle collapse.

Gas vesicles (GVs) are proteinaceous cylindrical shells found within bacteria or archea growing in aqueous environments and are composed primarily of two proteins, gas vesicle protein A and C (GvpA and GvpC). GVs exhibit strong performance as next-generation ultrasound contrast agents due to their gas-filled interior, tunable collapse pressure, stability in vivo and functionalizable exterior. However, the exact mechanism leading to GV collapse remains inconclusive, which leads to difficulty in predicting collapse pressures for different species of GVs and in extending favorable nonlinear response regimes. Here, we propose a two stage mechanism leading to GV loss of echogenicity and rupture under hydrostatic pressure: elastic buckling of the cylindrical shell coupled with condensation driven weakening of the GV membrane. Our goal is to therefore test whether the final fracture of the GV membrane occurs by the interplay of both mechanisms or purely through buckling failure as previously believed. To do so, we (1) compare the theoretical condensation and buckling pressures with that for experimental GV collapse and (2) describe how condensation can lead to plastic buckling failure. GV shell properties that are necessary input to this theoretical description, such as the elastic moduli and wettability of GvpA, are determined using molecular dynamics simulations of a novel structural model of GvpA that better represents the hydrophobic core. For GVs that are not reinforced by GvpC, this analytical framework shows that the experimentally observed pressures resulting in loss of echogenicity coincide with both the elastic buckling and condensation pressure regimes. We also found that the stress strain curve for GvpA wetted on both the interior and exterior exhibits a loss of mechanical stability compared to GvpA only wetted on the exterior by the bulk solution. We identify a pressure vs. vesicle size regime where condensation can occur prior to buckling, which may preclude nonlinear shell buckling responses in contrast imaging.

Close packings of identical proteins in small spherical capsids and similar proteinaceous shells.

Understanding the principles governing protein arrangement in viral capsids and structurally similar protein shells can enable the development of new antiviral strategies and the design of artificial protein cages for various applications. We study these principles within the context of the close packing problem, by analyzing dozens of small spherical shells assembled from a single type of protein. First, we use icosahedral spherical close packings containing 60T identical disks, where T ≤ 4, to rationalize the protein arrangement in twenty real icosahedral shells both satisfying and violating the paradigmatic Caspar-Klug model. We uncover a striking correspondence between the protein mass centers in the considered shells and the centers of disks in the close packings. To generalize the packing model, we consider proteins with a weak shape anisotropy and propose an interaction energy, minimization of which allows us to obtain spherical dense packings of slightly anisotropic structural units. In the case of strong anisotropy, we model the proteins as sequences of overlapping discs of different sizes, with minimum energy configuration not only resulting in packings, accurately reproducing locations and orientations of individual proteins, but also revealing that icosahedral packings that display the handedness of real capsids are energetically more favorable. Finally, by introducing effective disc charges, we rationalize the formation of inter-protein bonds in protein shells.

Hidden symmetry of the flavivirus protein shell and pH-controlled reconstruction of the viral surface.

Using recent Zika virus structural data we reveal a hidden symmetry of protein order in immature and mature flavivirus shells, violating the Caspar-Klug paradigmatic model of capsid structures. We show that proteins of the outer immature shell layer exhibit trihexagonal tiling, while proteins from inner and outer layers conjointly form a double-shelled close-packed structure, based on a common triangular spherical lattice. Within the proposed structural model, we furthermore rationalize the structural organization of misassembled non-infectious subviral particles that have no inner capsid. We consider a pH-controlled structural reconstruction of the outer shell from the trimeric to the dimeric state, and demonstrate that this transition, occurring during the virus maturation, can be induced by changes in protein charges at lower pH, leading to a decrease in the electrostatic interaction free energy. This transition could also be assisted by electrostatic attraction of shell proteins to the interposed lipid membrane substrate separating the shells.

Micromagnetic and morphological characterization of heteropolymer human ferritin cores.

The physical properties of in vitro iron-reconstituted and genetically engineered human heteropolymer ferritins were investigated. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy-loss spectroscopy (EELS), and 57Fe Mössbauer spectroscopy were employed to ascertain (1) the microstructural, electronic, and micromagnetic properties of the nanosized iron cores, and (2) the effect of the H and L ferritin subunit ratios on these properties. Mössbauer spectroscopic signatures indicate that all iron within the core is in the high spin ferric state. Variable temperature Mössbauer spectroscopy for H-rich (H21/L3) and L-rich (H2/L22) ferritins reconstituted at 1000 57Fe/protein indicates superparamagnetic behavior with blocking temperatures of 19 K and 28 K, while HAADF-STEM measurements give average core diameters of (3.7 ± 0.6) nm and (5.9 ± 1.0) nm, respectively. Most significantly, H-rich proteins reveal elongated, dumbbell, and crescent-shaped cores, while L-rich proteins present spherical cores, pointing to a correlation between core shape and protein shell composition. Assuming an attempt time for spin reversal of τ 0 = 10-11 s, the Néel-Brown formula for spin-relaxation time predicts effective magnetic anisotropy energy densities of 6.83 × 104 J m-3 and 2.75 × 104 J m-3 for H-rich and L-rich proteins, respectively, due to differences in surface and shape contributions to magnetic anisotropy in the two heteropolymers. The observed differences in shape, size, and effective magnetic anisotropies of the derived biomineral cores are discussed in terms of the iron nucleation sites within the interior surface of the heteropolymer shells for H-rich and L-rich proteins. Overall, our results imply that site-directed nucleation and core growth within the protein cavity play a determinant role in the resulting core morphology. Our findings have relevance to iron biomineralization processes in nature and the growth of designer's magnetic nanoparticles within recombinant apoferritin nano-templates for nanotechnology.

Modification of bacterial microcompartments with target biomolecules via post-translational SpyTagging.

Bacterial microcompartments (BMCs) are proteinaceous organelle-like structures formed within bacteria, often encapsulating enzymes and cellular processes, in particular, allowing toxic intermediates to be shielded from the general cellular environment. Outside of their biological role they are of interest, through surface modification, as potential drug carriers and polyvalent antigen display scaffolds. Here we use a post-translational modification approach, using copper free click chemistry, to attach a SpyTag to a target protein molecule for attachment to a specific SpyCatcher modified BMC shell protein. We demonstrate that a post-translationally SpyTagged material can react with a SpyCatcher modified BMC and show its presence on the surface of BMCs, enabling future investigation of these structures as polyvalent antigen display scaffolds for vaccine development. This post-translational 'click' methodology overcomes the necessity to genetically encode the SpyTag, avoids any potential reduction in expression yield and expands the scope of SpyTag/SpyCatcher vaccine scaffolds to form peptide epitope vaccines and small molecule delivery agents.

Abstract 1466: In Vitro Assembly of a Microcompartment from a Single Carboxysome Shell Protein

Abstract 1466: In Vitro Assembly of a Microcompartment from a Single Carboxysome Shell Protein

Screening of anti-liver fibrosis peptides from turtle shell protein using two-enzyme hydrolysis by molecular docking.

Turtle shell as a food residue of Pelodiscus sinensis (a type of edible aquatic animal) is widely used in Traditional Chinese Medicine for hepatic fibrosis therapy. Previous studies have demonstrated that the peptides (<6 kDa) derived from turtle shells are considered effective components. The protein of turtle shells has important potential as a source of bioactive peptides which may play a role as ingredients in functional foods. In the present study, the protein of turtle shell was hydrolyzed using a two-enzyme combination. It was found that the hydrolysates obtained by a combination of pepsin and trypsin showed the highest anti-liver fibrosis activity relative to other combinations in a cell viability assay. The hydrolysates were separated and purified by ultra-filtration (<6 kDa), gel filtration chromatography (GFC) and high-performance liquid chromatography (HPLC). Subsequently, the sequences of purified peptides were analyzed by liquid chromatography-mass spectrometry (LC-MS/MS). Molecular docking was used to analyze the interaction of these peptides with the transforming growth factor-β1 (TGF-β1) receptor. Two (GPPGVPGPGPL, TSLPVPAPV) of these novel peptides displayed lower binding energies to the TGF-β1 receptor (-8.18 kcal mol-1, -8 kcal mol-1). Finally, the above two peptides were synthesized chemically and their in vitro anti-liver fibrosis activity was verified by MTT assay. Among them, GPPGVPGPGPL showed a better in vitro anti-liver fibrosis activity (IC50: 80.13 μM). We established a method to obtain anti-liver fibrosis peptides from turtle shells by using bioactivity-guided isolation with molecular docking. Turtle shell protein is an excellent source of anti-liver fibrosis peptides which can offer therapeutic and commercial benefits as an ingredient in functional foods.

Crossover Dynamics of Rotavirus Disease under Fractional Piecewise Derivative with Vaccination Effects: Simulations with Real Data from Thailand, West Africa, and the US

Many diseases are caused by viruses of different symmetrical shapes. Rotavirus particles are approximately 75 nm in diameter. They have icosahedral symmetry and particles that possess two concentric protein shells, or capsids. In this research, using a piecewise derivative framework with singular and non-singular kernels, we investigate the evolution of rotavirus with regard to the effect of vaccination. For the considered model, the existence of a solution of the piecewise rotavirus model is investigated via fixed-point results. The Adam–Bashforth numerical method along with the Newton polynomial is implemented to deduce the numerical solution of the considered model. Various versions of the stability of the solution of the piecewise rotavirus model are presented using the Ulam–Hyres concept and nonlinear analysis. We use MATLAB to perform the numerical simulation for a few fractional orders to study the crossover dynamics and evolution and effect of vaccination on rotavirus disease. To check the validity of the proposed approach, we compared our simulated results with real data from various countries.

Molecular characterization of accripin11, a soluble shell protein with an acidic C-terminus, identified in the prismatic layer of the Mediterranean fan mussel Pinna nobilis (Bivalvia, Pteriomorphia).

We have identified a novel shell protein, accripin11, as a major soluble component of the calcitic prisms of the fan mussel Pinna nobilis. Initially retrieved from a cDNA library, its full sequence is confirmed here by transcriptomic and proteomic approaches. The sequence of the mature protein is 103 residues with a theoretical molecular weight of 11 kDa and is moderately acidic (pI 6.74) except for its C-terminus which is highly enriched in aspartic acid. The protein exhibits a peculiar cysteine pattern in its central domain. The full sequence shares similarity with six other uncharacterized molluscan shell proteins from the orders Ostreida, Pteriida and Mytilida, all of which are pteriomorphids and produce a phylogenetically restricted pattern of nacro-prismatic shell microstructures. This suggests that accripin11 is a member of a family of clade-specific shell proteins. A 3D model of accripin11 was predicted with AlphaFold2, indicating that it possesses three short alpha helices and a disordered C-terminus. Recombinant accripin11 was tested in vitro for its ability to influence the crystallization of CaCO3 , while a polyclonal antibody was able to locate accripin11 to prismatic extracts, particularly in the acetic acid-soluble matrix. The putative functions of accripin11 are further discussed in relation to shell biomineralization.