Coupled European and Greenland last glacial dust activity driven by North Atlantic climate.

Centennial-scale mineral dust peaks in last glacial Greenland ice cores match the timing of lowest Greenland temperatures, yet little is known of equivalent changes in dust-emitting regions, limiting our understanding of dust-climate interaction. Here, we present the most detailed and precise age model for European loess dust deposits to date, based on 125 accelerator mass spectrometry 14C ages from Dunaszekcso, Hungary. The record shows that variations in glacial dust deposition variability on centennial-millennial timescales in east central Europe and Greenland were synchronous within uncertainty. We suggest that precipitation and atmospheric circulation changes were likely the major influences on European glacial dust activity and propose that European dust emissions were modulated by dominant phases of the North Atlantic Oscillation, which had a major influence on vegetation and local climate of European dust source regions.

The Biomineralization Proteome: Protein Complexity for a Complex Bioceramic Assembly Process.

There are over 62 different biominerals on Earth and a diverse array of organisms that generate these biominerals for survival. This review will introduce the process of biomineralization and the current understanding of the molecular mechanisms of mineral formation, and then comparatively explore the representative secretomes of two well-documented skeletal systems: vertebrate bone (calcium phosphate) and invertebrate mollusk shell (calcium carbonate). It is found that both skeletal secretomes have gross similarities and possess proteins that fall into four functional categories: matrix formers, nucleation assisters, communicators, and remodelers. In many cases the mineral-associated matrix former and nucleation assister sequences in both skeletal systems are unique and possess interactive conserved globular domains, intrinsic disorder, post-translational modifications, sequence redundancy, and amyloid-like aggregation-prone sequences. Together, these molecular features create a protein-based environment that facilitates mineral formation and organization and argue in favor of conserved features that evolve from the mollusk shell to bone. Interestingly, the mollusk shell secretome appears to be more complex compared to that of bone tissue, in that there are numerous protein subcategories that are required for the nucleation and organization of inner (nacre) and outer (prismatic) calcium carbonate regions of the shell. This may reflect the organizational and material requirements of an exoskeletal protective system.

Comparative studies on the anti-wear behavior of prismatic structures in different shell species.

Prismatic structure is mainly located in the outer layer of mollusk shells. However, there is limited studies on their resistance to wear and the underlying mechanisms. The Vicker's hardness and sliding anti-wear properties of prismatic structures in four species of mollusk shells were systematically investigated for comparisons in the present work. The crystalline types, organic matrix content, structural arrangement, and dimension of prisms are varied among different species. The hardness and wear properties of prismatic structures are, in the first place, determined by the crystalline type, i.e., the aragonite prismatic structures are harder and more wear-resisting than the calcite types. The primary failure mechanism in the prismatic structure during wear tests is three-body abrasion. The volume of the crushed prism particles is directly related to the thickness of organic interface and the hardness of prisms. The organic sheaths form organic films during sliding, and thus lubricate the friction interface to some extent, but higher organic content leads to a wider interface, resulting in a higher plough force at the edge of prisms. A higher plough force gives rise to a severe three-body abrasion. Long and straight prisms perpendicular to the shell surface present a higher wear resistance. Too thin prisms cannot bear the plough force. Therefore, the anti-wear properties of prismatic structures are governed by the joint action of crystalline types, organic matrix, structural arrangement and dimension of basic building blocks.

Preliminary Analysis of Hydrodynamic Drag Reduction and Fouling Resistance of Surfaces Inspired by the Mollusk Shell, Dosinia juvenilis.

Many species of plants and animals show an ability to resist fouling with surface topographies tailored to their environments. The mollusk species Dosinia juvenilis has demonstrated the ability to resist the accumulation of fouling on its outer surface. Understanding the functional mechanism employed by nature represents a significant opportunity for the persistent challenges of many industrial and consumer applications. Using a biomimetic approach, this study investigates the underlying hydrodynamic mechanisms of fouling resistance through Large Eddy simulations of a turbulent boundary layer above a novel ribletted surface topography bio-inspired by the Dosinia juvenilis. The results indicate a maximum drag reduction of 6.8% relative to a flat surface. The flow statistics near the surface are analogous to those observed for other ribletted surfaces in that the appropriately sized riblets effectively reduce the spanwise and wall-normal velocity fluctuations near the surface. This study supports the understanding that nature employs ribletted surfaces toward multiple functionalities including the considered drag reduction and fouling resistance.

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.

A unique methionine-rich protein-aragonite crystal complex: Structure and mechanical functions of the Pinctada fucata bivalve hinge ligament.

The bivalve hinge ligament holds the two shells together. The ligament functions as a spring to open the shells after they were closed by the adductor muscle. The ligament is a mineralized tissue that bears no resemblance to any other known tissue. About half the ligament is composed of a protein-rich matrix, and half of long and extremely thin segmented aragonite crystals. Here we study the hinge ligament of the pearl oyster Pinctada fucata. FIB SEM shows that the 3D organization is remarkably ordered. The full sequence of the major protein component contains a continuous segment of 30 repeats of MMMLPD. There is no known homologous protein. Knockdown of this protein prevents crystal formation, demonstrating that the integrity of the matrix is necessary for crystals to form. X-ray diffraction shows that the aragonite crystals are more aligned in the compressed ligament, indicating that the crystals may be actively contributing to the elastic properties. The fusion interphase that joins the ligament to the shell nacre is composed of a prismatic mineralized tissue with a thin organic-rich layer at its center. Nanoindentation of the dry interphase shows that the elastic modulus of the nacre adjacent to the interphase gradually decreases until it approximates that of the interphase. The interphase modulus slightly increases until it matches the ligament. All these observations demonstrate that the ligament shell complex is a remarkable biological tissue that has evolved unique properties that enable bivalves to open their shell effectively innumerable times during the lifetime of the animal. STATEMENT OF SIGNIFICANCE: The hinge ligament shell complex is a unique functioning structural tissue whose elastic properties enable the shell to open without expending energy. Methionine-rich proteins are not known elsewhere raising fundamental questions about secondary and tertiary structures contributing to its elastic properties. The segmented and extremely thin aragonite crystals embedded in this matrix may also have unexpected elastic materials properties as they flex during compression. The structure of the interphase comprises a fascinating biological joint that connects two very different materials. The interphase materials, including the nacre, are graded with respect to elastic modulus so as to approximately match the connecting components. The interphase incorporates a thin organic rich layer that presumably functions as a gasket. This study raises many fundamental questions relevant to the diverse fields of protein chemistry, biomineralization and biological materials.

Biomacromolecules within bivalve shells: Is chitin abundant?

Bivalve shells are inorganic-organic nanocomposites whose material properties outperform their purely inorganic mineral counterparts. Most typically the inorganic phase is a polymorph of CaCO3, while the organic phase contains biopolymers which have been presumed to be chitin and/or proteins. Identifying the biopolymer phase is therefore a crucial step in improving our understanding of design principles relevant to biominerals. In this work we study seven shells; four are examples of nacroprismatic shells (Alathyria jacksoni, Pinctada maxima, Hyriopsis cumingii and Cucumerunio novaehollandiae), one homogeneous (Arctica islandica), and two are crossed lamellar (Callista kingii, Tridacna gigas). Both intact shells, their organic extracts as isolated after decalcification in acid, and the periostracum overlay have been studied by solid-state CP-MAS NMR, FTIR, SEM and chemical analysis. In none of the shells examined in this work do we find a significant contribution to the organic fraction from chitin or its derivatives despite popular models of bivalve biomineralization which assume abundant chitin in the organic fraction of mollusk bivalve shells. In each of the nacroprismatic extracts the 13C NMR spectra represent similar proteinaceous material, Ala and Gly-rich and primarily organized as ß-sheets. A different, yet highly conserved protein was found in the periostracum covering each of the three nacreous shells studied. The Arctica islandica shells with homogeneous microstructure contained proteins which do not appear to be silk-like, while in the crossed lamellar shells we extracted too little organic matter to characterize. STATEMENT OF SIGNIFICANCE: Hydrophobic macromolecules are structural components within the calcareous inorganic matrix of bivalve shells and are responsible for enhanced materials properties of the biominerals. Prevalent models suggest that chitin is such major hydrophobic component. Contrary to that we show that chitin is rare within the hydrophobic biopolymers which primarily consist of proteinaceous matter with structural motifs as silk-like ß-sheets, or others yet to be determined. Recognizing that diverse proteinaceous motifs, devoid of abundant chitin, can yield the optimized mechanical properties of bivalve shells is critical both to understand the mechanistic pathways by which they regulate biomineralization and for the design of novel bioinspired materials.

Experimental and numerical investigations of Otala lactea's shell-I. Quasi-static analysis.

At the first glance, mollusk shells may seem complex spatial structures with interesting shapes, forms and colors. However, from an engineering point of view, they are mechanical barriers which provide remarkable protection against environmental factors. These biological composites which exhibits an attractive combination of stiffness, strength and toughness, may be mimicked in bio-inspired materials. In the present work, a mathematical method is used to develop comprehensive three-dimensional (3D) numerical models of mollusk shells. The models are employed to study the mechanical behavior of the shells under static loading conditions. Numerical analyses are conducted using ANSYS finite element (FE) codes. A combination of indentation testing and scanning electron microscopy (SEM) is utilized to confirm the validity of the models and the solving procedures. A good agreement is observed between the shape, size and location of the failure obtained from experimental tests and numerical predictions. The results indicate that the columella increases the ability of mollusk shells to withstand applied mechanical forces without failure. Further, it can be concluded that the coiling geometry of the shells adequately modifies the stress distribution and reduces the stress concentration.