Electron backscatter diffraction is used to characterize the transition interface between aragonite prisms and nacre in two species of freshwater molluscs, Anodonta anatina (Linnaeus, 1758) and Anodonta cygnea (L. 1758). In the duck mussel, Anodonta anatina, the shell thickness is comprised mainly of nacre with only a thin outer prismatic layer, whereas in the swan mussel, A. cygnea, the shell comprises a greater thickness of aragonite prisms relative to the nacreous layer. In A. anatina, the prism−nacre interface is flat and featureless. In A. cygnea, the nacre below the base of the prisms is characterized by distinct concave footholds. In both species, the c-axis of aragonite nanogranules comprising the prisms is parallel with the prism length. This crystallographic orientation, with the c-axis perpendicular to the shell exterior, occurs in the nacreous layer and thus is conserved throughout the shell thickness. In A. cygnea alternate prisms have a crystallographic orientation with the c-axis deviating from the prism long axis by approximately 20 deg. The initial nacreous layer adopts the crystallographic orientation of the preceding prisms and subsequent nacreous laminae are oriented in register with the bulk nacre. This is consistent with the hypothesis that nacre evolved through horizontal partitioning of prisms.
Summary Large single crystals (up to 1 mm in each dimension) of the B800–850 antenna complex from Rhodopseudomonas acidophila strain 10050 have been grown in the presence of β-octyl-glucoside. These crystals have the space group R32 and unit cell dimensions of a = b = 119.9 Å and c = 297.0 Å. Recently we have improved our crystallization procedures so that all crystals now diffract reliably to beyond 3.5 Å, with some diffracting to below 3 Å. A range of isomorphous heavy atom derivatives have been prepared and we are now engaged in locating the heavy atom sites within the unit cell.
Abstract— The molecular structure of the light‐harvesting complex 2 (LH2) bacteriochlorophyll‐protein antenna complex from the purple non‐sulfur photosynthetic bacterium Rhodopseudomonas acidophila , strain 10050 provides the positions and orientations of the 27 bacteriochlorophyll (BChl) molecules in the complex. Our structure‐based model calculations of the distinctive optical properties (absorption, CD, polarization) of LH2 in the near‐infrared region use a point‐monopole approximation to represent the BChl Q y transition moment. The results of the calculations support the assignment of the ring of 18 closely coupled BChl to B850 (BChl absorbing at 850 nm) and the larger diameter, parallel ring of 9 weakly coupled BChl to B800. All of the significantly allowed transitions in the near infrared are calculated to be perpendicular to the C9 symmetry axis, in agreement with polarization studies of this membrane‐associated complex. To match the absorption maxima of the B800 and B850 components using a relative permittivity (dielectric constant) of 2.1, we assign different site energies (12 500 and 12260 cm −1 , respectively) for the Q y transitions of the respective BChl in their protein binding sites. Excitonic coupling is particularly strong among the set of B850 chromophores, with pairwise interaction energies nearly 300 cm between nearest neighbors, comparable with the experimental absorption bandwidths at room temperature. These strong interactions, for the full set of 18 B850 chromophores, result in an excitonic manifold that is 1200 cm −1 wide. Some of the upper excitonic states should result in weak absorption and perhaps stronger CD features. These predictions from the calculations await experimental verification.
The common blue mussel, Mytilus edulis, has a bimineralic shell composed of approximately equal proportions of the two major polymorphs of calcium carbonate: calcite and aragonite. The exquisite biological control of polymorph production is the focus of research interest in terms of understanding the details of biomineralisation and the proteins involved in the process of complex shell formation. Recent advances in ease and availability of pyrosequencing and assembly have resulted in a sharp increase in transcriptome data for invertebrate biominerals. We have applied Roche 454 pyrosequencing technology to profile the transcriptome for the mantle tissue of the bivalve M. edulis. A comparison was made between the results of several assembly programs: Roche Newbler assembler versions 2.3, 2.5.2 and 2.6 and MIRA 3.2.1 and 3.4.0. The Newbler and MIRA assemblies were subsequently merged using the CAP3 assembler to give a higher consensus in alignments and a more accurate estimate of the true size of the M. edulis transcriptome. Comparison sequence searches show that the mantle transcripts for M. edulis encode putative proteins exhibiting sequence similarities with previously characterised shell proteins of other species of Mytilus, the Bivalvia Pinctada and haliotid gastropods. Importantly, this enhanced transcriptome has detected several transcripts that encode proteins with sequence similarity with previously described shell biomineral proteins including Shematrins and lysine-rich matrix proteins (KRMPs) not previously found in Mytilus.
Biomineralization is the process where biological systems produce well-defined composite structures such as shell, teeth, and bones. Currently, there is substantial momentum to investigate the processes implicated in biomineralization and to unravel the complex roles of proteins in the control of polymorph switching. An understanding of these processes may have wide-ranging significance in health care applications and in the development of advanced materials. We have demonstrated a microfluidic approach toward these challenges. A reversibly sealed T-junction microfluidic device was fabricated to investigate the influence of extrapallial (EP) fluid proteins in polymorph control of crystal formation in mollusk shells. A range of conditions were investigated on chip, allowing fast screening of various combinations of ion, pH, and protein concentrations. The dynamic formation of crystals was monitored on chip and combined with in situ Raman to reveal the polymorph in real time. To this end, we have demonstrated the unique advantages of this integrated approach in understanding the processes involved in biomineralization and revealing information that is impossible to obtain using traditional methods.
The superimposed layers of the true oyster shell have distinct morphology. The shells are mainly calcitic, comprising an outer prismatic region and inner foliated structure that is frequently interrupted by lenses of chalky calcitic deposits. Aragonite is restricted to the myostracum and ligament. Electron backscatter diffraction (EBSD) analysis has shown that despite the variations in structural morphology, the mineralized layers of the oyster shell maintain a single crystallographic orientation with the crystallographic c-axis orientated perpendicular to outer and inner shell surfaces. Varying crystal morphology, while maintaining crystallographic unity, may be an evolutionary trait that forms a crack-resistant shell with optimum strength and flexibility.
Biominerals have attracted investigations for centuries due to their enormous diversity and extraordinary functionality, which are un-matched by man-made materials. Using microfluidics, we have provided direct experimental evidence that an extrapallial (EP) 28kDa protein can influence the morphology, structure and polymorph that is laid down in the shell ultrastructure. Crucially, this influence is predominantly dependent on the existence of an EP protein concentration gradient and its consecutive interaction with Ca 2+ ions. Furthermore, the functional similarity was found using an engineered counterpart protein (i.e. cloned and expressed), demonstrating a new biomimetic strategy to develop functional biomaterials.
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