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PubMed1996

Calcium oxalate crystallization in urine of healthy men and women: a comparative study.

This study aimed to compare calcium oxalate (CaOx) crystallization in undiluted urine from healthy men and women with the object of clarifying the difference in stone incidence between the two sexes. Twenty-four hour urine specimens were collected from 37 men and 28 women. Urinary pH, and concentrations of Ca, oxalate and urate were measured, and indices of crystallization determined by Coulter Counter particle analysis following induction of CaOx crystallization by addition of oxalate. The amount of oxalate required to induce crystallization was significantly (p < 0.01) higher in females than in males, as was the overall particle volume deposited after 90 minutes incubation (p < 0.006). Scanning electron microscopy revealed larger individual crystals in female urine, and a greater degree of crystal aggregation in male urine, although the average overall size of the precipitated crystal particles did not differ between the two sexes. There were no significant differences between men and women with regard to median pH, or Ca and oxalate concentrations, but the median urate concentrations were slightly, but significantly, higher (p < 0.05) in the women's urines than in the men's. It was concluded that the greater risk of CaOx stones in men is related to an increased propensity to nucleate CaOx crystals per se, rather than to a tendency to form larger crystalline particles.

Adolescent↗
PubMed2002

Mechanism of CIT-6 and VPI-8 crystallization from zincosilicate gels.

The crystallisation of CIT-6, a large-pore zincosilicate with the framework topology of zeolite Beta and synthesised from clear hydrogels that contain, tetraethylammonium (TEA+), Li+ and Zn2+ cations, proceeds initially through the formation of an amorphous solid that incorporates all the initial Zn species. Nucleation of the *BEA phase is effected by reorganisation of the amorphous phase, whereas crystal growth involves the incorporation of soluble species also. A highly crystalline CIT-6 material is obtained after 164 h of synthesis at 140 degrees C. Scanning electron microscopy (SEM) shows that this sample exhibits two different types of crystals: well-defined pseudo-cubic crystals and rounded crystals. The latter has a broad crystal-size distribution. If crystallisation is continued with longer synthesis times, the VPI-8 crystalline phase appears, and a new population of needle-shaped crystals is detected in the SEM images. This new crystalline phase is nucleated on the surface of the rounded CIT-6 crystals, which disappear as the crystallisation progresses, while no changes are observed in the population of pseudo-cubic CIT-6 crystals. At higher crystallisation temperatures these phase transformations are accelerated, and the formation of VPI-8 is favoured over that of CIT-6.

Journal Article↗
PubMed2005

Structural rationalisation of co-crystals formed between trithiocyanuric acid and molecules containing hydrogen bonding functionality.

Crystallisation of trithiocyanuric acid (TTCA) from various organic solvents that have hydrogen bonding capability (acetone, 2-butanone, dimethylformamide, dimethyl sulfoxide, methanol and acetonitrile) leads to the formation of co-crystals in which the solvent molecules are incorporated together with TTCA in the crystal structure. Structure determination by single-crystal X-ray diffraction reveals that these co-crystals can be classified into different groups depending upon the topological arrangement of the TTCA molecules in the crystal structure. Thus, three different types of single-tape arrangements of TTCA molecules and one type of double-tape arrangement of TTCA molecules are identified. In all co-crystals, hydrogen-bonding interactions are formed through the involvement of N-H bonds of TTCA molecules in these tapes and the other molecule in the co-crystal. Detailed rationalisation of the structural properties of these co-crystals is presented.

Journal Article↗
PubMed2004

Molecular recognition and crystal energy landscapes: an X-ray and computational study of caffeine and other methylxanthines.

We introduce a new approach to crystal-packing analysis, based on the study of mutual recognition modes of entire molecules or of molecular moieties, rather than a search for selected atom-atom contacts, and on the study of crystal energy landscapes over many computer-generated polymorphs, rather than a quest for the one most stable crystal structure. The computational tools for this task are a polymorph generator and the PIXEL density sums method for the calculation of intermolecular energies. From this perspective, the molecular recognition, crystal packing, and solid-state phase behavior of caffeine and several methylxanthines (purine-2,6-diones) have been analyzed. Many possible crystal structures for anhydrous caffeine have been generated by computer simulation, and the most stable among them is a thermodynamic, ordered equivalent of the disordered phase, revealed by powder X-ray crystallography. Molecular recognition energies between two caffeine molecules or between caffeine and water have been calculated, and the results reveal the largely predominant mode to be the stacking of parallel caffeine molecules, an intermediately favorable caffeine-water interaction, and many other equivalent energy minima for lateral interactions of much less stabilization power. This last indetermination helps to explain why caffeine does not crystallize easily into an ordered anhydrous structure. In contrast, the mono- and dimethylxanthines (theophylline, theobromine, and the 1,7-isomer, for which we present a single-crystal X-ray study and a lattice energy landscape) do crystallize in anhydrous form thanks to the formation of lateral hydrogen bonds.

Caffeine↗
PubMed2005

Organic intercalation material: reversible change in interlayer distances by guest release and insertion in sandwich-type inclusion crystals of cholic acid.

Cholic acid (CA) forms inclusion crystals that have a sandwich-type lamellar structure constructed by the alternative stacking of host bilayers and guest layers. Five disubstituted benzenes, o-toluidine, m-fluoroaniline, o-chlorotoluene, o-bromotoluene, and indene, are accommodated in the two-dimensional void space between the host bilayers at 1:2 host-guest stoichiometries. Thermal gravimetric analysis of the inclusion crystals revealed that all the guest molecules, except o-toluidine, are released in two separate steps, indicating the formation of intermediate crystals after the first guest release. Adequate heat treatment of the four inclusion crystals induces release of half or three quarters of the guest molecules. X-ray diffraction patterns of the intermediate crystals revealed that the crystals have a bilayer structure the same as those of the common CA inclusion crystals. They have one-dimensional cavities, in which the guest molecules are included at a 1:1 or 2:1 host-guest stoichiometry. These facts indicate that the host bilayers move 1.6-4.5 A perpendicular to the layer direction by desorption of the guest molecules. Furthermore, a reverse structural change is also achieved by absorption of the guest molecules to regenerate the starting sandwich-type inclusion crystals. This reversible change in the host bilayer by the guest sorption and desorption is a novel example of organic intercalation materials.

Journal Article↗
PubMed1997

Solubilization of lead from crystal dust in protein solution (pseudointerstitial fluid) and gastric juice.

Since several workers engaged in polishing and engraving crystal articles were found to have higher than average blood levels of lead (560 micrograms/liter, range 80-560 micrograms/liter), we investigated the hypothesis that crystal dust releases lead in the human body. To test the hypothesis, two types of crystal polishing dusts, having different lead contents, were mixed with human serum diluted 1:3 (pseudointerstitial fluid), gastric juice, and phosphate buffer at pH 9. After 14 days of contact, the diluted serum had extracted 0.620% of the lead in the crystal dust (particle size < 20 microns) containing 25.2% lead and 0.425% of that containing 19.9% lead. After 48 hr in gastric juice, 0.235 and 0.556% of the lead was extracted from crystal dusts (unsieved crystal dusts) containing 25.2 and 19.9% lead, respectively. After 28 days in alkaline solution, 0.358 and 0.304% of the lead was extracted respectively from the same two crystal dusts (unsieved crystal dusts).

Dust↗
PubMed1997

Interfacial Aggregation of Bovine Serum Albumin Related to Crystallization Conditions Studied by Total Internal Reflection Fluorescence

Total internal reflection fluorescence (TIRF) was used to examine adsorption and interfacial aggregation of bovine serum albumin (BSA) from solvent conditions that are known to promote BSA crystallization. In the absence of a crystallizing agent (thermodynamically good solvent conditions), adsorption from a 0.1 mg/mL BSA solution in 50 mM phosphate buffer, pH 6.2, 25&deg;C, results in formation of not more than monolayer protein films on both hydrophilic and hydrophobic surfaces. However, in the presence of ammonium sulfate, which is used as an agent to crystallize BSA, adsorption yields a relatively thick multilayer protein film. The interfacial aggregation is sensitive to hydrophobicity of the substrate as well as to the prehistory of adsorption. A hydrophilic substrate promotes formation of thicker protein films than a hydrophobic one. For example, in the presence of 2.13 M ammonium sulfate, BSA adsorption during approximately 10 h yields approximately a 20-monolayer film on the quartz surface, in contrast to a 6-7 monolayer film on the hydrophobic surface. Rates of multilayer adsorption and desorption and the ultimate thickness of the multilayer protein film critically depend on the concentration of crystallizing agent. The rates correlate with the osmotic second virial coefficient, B22, which has been shown to be a predictor for protein crystallization. In the range of B22 values known as a "crystallization slot," the multilayer adsorption demonstrates a uniform rate of film growth. Noncrystallizing solvents do not exhibit this feature. The TIRF technique can be used to investigate molecular mechanisms of crystal growth and growth cessation as well as epitaxial and pseudoepitaxial growth using protein crystals grown at or attached to the surface. TIRF provides a sensitive and powerful tool to probe in situ and in real time the interactions of dissolved protein with a growing protein solid phase. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2000

Kinetics of Crystallization in n-Hexadecane and Cocoa Butter Oil-in-Water Emulsions Accounting for Droplet Collision-Mediated Nucleation.

Droplet collision is shown to be important in the propagation of nucleation through supercooled oil-in-water emulsions by the use of a novel membrane technique. On the other hand, nucleation mediated by Tween 20 micelles is shown to be of relatively much less importance in both n-hexadecane and cocoa butter oil-in-water emulsions. The droplet collision phenomenon probably occurs via a surfactant bridge between the colliding droplets. When this process is taken into account we show that the Turnbull model for crystal nucleation kinetics explains very well nucleation in cocoa butter oil-in-water emulsions by seed crystals. On the basis of this model we characterized the seed crystals in cocoa butter via isothermal crystallization studies at 14.2, 15.0, 15.5, and 15.8 degrees C. We suggest that there are few seed crystals whose size exceeds 0.28 µm at 80 degrees C. In our cocoa butter samples there were between 10(16) and 10(17) seed crystals m(-3) whose average size we inferred to be less than 0.09 µm. A value of 0.133 mJ m(-2) is obtained for the Gibbs free energy of the nucleating surface in our West African cocoa butter samples. There is evidence that the alpha-polymorph of POS comprises the nucleating layer in the seed crystal. There is no evidence that surfactant influences the primary nucleation of oil crystals. However, the surfactant has a big effect on the kinetics of the secondary nucleation process, mediated by droplet collision. Copyright 2000 Academic Press.

Journal Article↗
PubMed1993

Crystallization and preliminary X-ray diffraction analysis of two conformations of intact human antithrombin.

Human antithrombin has been crystallized by microdialysis at pH 6.7 using 18% (w/v) polyethylene glycol-4000 as precipitant. Under these conditions two crystal forms grew. The first started growing after ten days, diffracted to 3.0 A resolution and belongs to the monoclinic space group P2(1) with two molecules in the asymmetric unit and unit cell dimensions a = 70.1 A, b = 101.5 A, c = 90.5 A and beta = 105.9 A. The other crystal form took more than three months to appear, diffracted to 5.5 A and belongs to the hexagonal space group of either P6(1) or P6(5) with unit cell dimensions of a = b = 99.3 A and c = 152.9 A and two molecules in the asymmetric unit. The antithrombin redissolved from the monoclinic crystals was shown both by SDS-polyacrylamide gel electrophoresis and by protein sequence analysis to be intact while that from the hexagonal crystals was cleaved in the reactive centre loop between the P'2 and P'3 (i.e. Leu-Asn) residues. Further analysis of the intact inhibitor from the monoclinic crystals indicated that the antithrombin was present in two different conformations; an active form which could inhibit thrombin and form a stable complex with the protease, and a form which was inactive as an inhibitor and which also did not act as a substrate for thrombin. This latter form also had a low affinity for heparin and in these ways resembles latent antithrombin. The active material from the monoclinic crystals had an association rate constant with thrombin in the presence of heparin (kass) of 7.5 x 10(7) M-1 s-1 (kass for native antithrombin = 8.2 (+/- 1.0) x 10(7) M-1 s-1) indicating it still had effective heparin cofactor activity. X-ray diffraction analysis also suggests that two different protein conformations exist within the monoclinic crystals. Whereas the rotation function peak heights are equal for both molecules in the asymmetric unit using the structure of intact ovalbumin as a search model, one of the two molecules gives a much clearer signal than the other when the structures of the two cleaved serpins, alpha 1-antitrypsin and alpha 1-antichymotrypsin are used.

Antithrombins↗
PubMed1994

Crystals of glutamine-binding protein in various conformational states.

Crystals of glutamine-binding protein (GlnBP) in various conformational states have been obtained. Crystals of the ligand-free "open" state (denoted form B) have unit cell dimensions a = 86.3 A, b = 86.3 A, c = 81.5 A, alpha = beta = gamma = 90 degrees and diffract to about 2.3 A resolution. An analysis of the intensity data using an Requiv plot indicates that the crystal system is orthorhombic, space group P2(1)2(1)2(1). Crystals of the ligand-bound "open" state (form B*) are obtained by soaking form B crystals with glutamine (Gln) and diffract to about 1.9 A. Crystals of the GlnBP-Gln complex in a ligand-bound "closed" state (form C) belong to space group P2(1)2(1)2(1) with a = 62.0 A, b = 65.7 A and c = 121.8 A and diffract to about 2.3 A. Crystals of a selenomethionyl GlnBP (form B') are isomorphous to form B crystals and diffract to about 2.1 A resolution.

Carrier Proteins↗
PubMed1998

Structures of two novel crystal forms of Naja naja naja phospholipase A2 lacking Ca2+ reveal trimeric packing.

Three crystal forms of Naja naja naja phospholipase A2 were discovered through random crystallization screening, including two heretofore uncharacterized forms. The crystallization conditions for both of these novel crystal forms are Ca(2+)-free whereas previously reported conditions include Ca2+. One of the new crystal forms has a cubic lattice in the space group P2(1)3 (a = b = c = 69.24 A), the other has an orthorhombic lattice in the space group P2(1)2(1)2(1) (a = 67.22 A, b = 73.48 A, c = 87.52 A) and a previously characterized crystal belong to the tetragonal space group P4(3)2(1)2 (a = b = 88.6 A, c = 107.4 A). The structure from the cubic crystal form has been determined to 1.8 A and refined to an R-factor of 17% while the structure from the orthorhombic form has been determined to 2.65 A and has been refined to an R-factor of 21%. The determination of the cubic structure extends the resolution to which structures of this molecule have been determined from 2.3 A to 1.8 A. The two newly determined structures, in combination with the previously determined structure, generate an informative structural ensemble from which structural changes due to Ca2+, which is required for catalysis, and the effect of crystal contacts on side-chain conformations and oligomeric association can be inferred. Both of the newly determined structures reveal a trimeric oligomer as observed in the tetragonal structure; this appears to be a unique feature of the Naja naja naja enzyme.

Animals↗
PubMed1998

Three-dimensional crystals of Ca2+-ATPase from sarcoplasmic reticulum: merging electron diffraction tilt series and imaging the (h, k, 0) projection.

Electron crystallography offers an increasingly viable alternative to X-ray crystallography for structure determination, especially for membrane proteins. The methodology has been developed and successfully applied to 2D crystals; however, well-ordered thin, 3D crystals are often produced during crystallization trials and generally discarded due to complexities in structure analysis. To cope with these complexities, we have developed a general method for determining unit cell geometry and for merging electron diffraction data from tilt series. We have applied this method to thin, monoclinic crystals of Ca2+-ATPase from sarcoplasmic reticulum, thus characterizing the unit cell and generating a 3D set of electron diffraction amplitudes to 8 A resolution with tilt angles up to 30 degrees. The indexing of data from the tilt series has been verified by an analysis of Laue zones near the (h, k, 0) projection and the unit cell geometry is consistent with low-angle X-ray scattering from these crystals. Based on this unit cell geometry, we have systematically tilted crystals to record images of the (h, k, 0) projection. After averaging the corresponding phases to 8 A resolution, an (h, k, 0) projection map has been calculated by combining image phases with electron diffraction amplitudes. This map contains discrete densities that most likely correspond to Ca2+-ATPase dimers, unlike previous maps of untilted crystals in which molecules from successive layers are not aligned. Comparison with a projection structure from tubular crystals reveals differences that are likely due to the conformational change accompanying calcium binding to Ca2+-ATPase.

Calcium-Transporting ATPases↗
PubMed1999

The pH-dependent structural variation of complementarity-determining region H3 in the crystal structures of the Fv fragment from an anti-dansyl monoclonal antibody.

The Fv fragment from an anti-dansyl antibody was optimally crystallized into two crystal forms having slightly different lattice dimensions at pH 5.25 and 6.75. The two crystal structures were determined and refined at high resolution at 112 K (at 1.45 A for the crystal at pH 5.25 and at 1.55 A for that at pH 6.75). In the two crystal structures, marked differences were identified in the first half of CDRH3 s having an amino acid sequence of Ile95H-Tyr96H-Tyr97H-His98H-Tyr99H-Pro1 00H-Trp100aH-Phe100bH-Ala101H- Tyr102H. NMR pH titration experiments revealed the p Kavalues of four histidine residues (His27dL, His93L, His55H and His98H) exposed to solvent. Only His98H (p Ka=6.3) completely changed its protonation state between the two crystallization conditions. In addition, the environmental structures including hydration water molecules around the four histidine residues were carefully compared. While the hydration structures around His27dL, His93L and His55H were almost invariant between the two crystal structures, those around His98Hs showed great difference in spite of the small conformational difference of His98H between the two crystal structures. These spectroscopic and crystallographic findings suggested that the change in the protonation state in His98H was responsible for the structural differences between pH 5.25 and 6.75. In addition, the most plausible binding site of the dansyl group was mapped into the present structural models with our previous NMR experimental results. The complementarity-determining regions H1, H3 and the N-terminal region in the VH domain formed the site. The side-chain of Tyr96H occupied the site and interacted with Phe27H of H1, giving a clue for the binding mode of the dansyl group in the site.

Antibodies, Monoclonal↗
PubMed1998

A randomized clinical trial of topical cysteamine disulfide (cystamine) versus free thiol (cysteamine) in the treatment of corneal cystine crystals in cystinosis.

In nephropathic cystinosis, corneal cystine crystals cause severe photophobia and corneal erosions. Topical cysteamine dissolves these crystals, but cannot be marketed because it rapidly oxidizes to the disulfide form, cystamine, at room temperature. Since cystamine itself could be used commercially, we compared the efficacy of cystamine and cysteamine with respect to cystine crystal dissolution in a randomized, double-masked clinical trial. One eye each of 14 patients with cystinosis was randomized to either cystamine or cysteamine, 0.5%, with 0.01% benzalkonium chloride; the companion eye was treated with the alternate preparation. Corneal crystals were photographed and a density score was assigned to each slide based on 13 standard slides. After 8-20 months, 6 patients showed significant reduction of the corneal crystal score in only one eye. In each case, the improved eye was the cysteamine-treated eye. Theoretically, cysteamine should dissolve both intracellular and extracellular crystals, whereas cystamine should dissolve only intracellular crystals because it must first be reduced to the free thiol by the cytoplasmic-reducing environment. Hence, the lack of efficacy of the disulfide cystamine suggests that some corneal cystine crystals in cystinosis patients are extracellular, and that another form of stable, topical cysteamine must be developed for cystinosis patients.

Administration, Topical↗
PubMed1984

Decavanadate is responsible for vanadate-induced two-dimensional crystals in sarcoplasmic reticulum.

Two-dimensional protein crystals of the calcium pump protein of sarcoplasmic reticulum (SR) from fast skeletal muscle were induced using Na3VO3 as first described by Dux and Martonosi. These crystals exhibit repeat rows approximately 11 nm apart which contain discrete units with approximately 7 nm repeats. Four different methods of sample preparation for electron microscopy, i.e., negative staining, freeze-drying, freeze-fracturing, and thin-sectioning electron microscopy, each give complimentary repeat units. The SR-membrane crystals exhibit surface structure by the freeze-drying technique and row-like structures on the normally smooth outer face of normal SR. The formation of the membrane crystals is dependent on the pH and concentration of the vanadate. Only conditions favoring the presence of decavanadate yield crystals. At low concentrations and neutral pH, decavanadate is unstable and with time converts to smaller oligomers and the monomer. The presence of membrane crystals was correlated with the life span of the decavanadate. Membrane crystals were obtained in the SR membrane from fast twitch muscle from light and heavy SR, referable to longitudinal and terminal cisternae as well as from reconstituted SR. Canine cardiac SR did not crystallize under these conditions.

Animals↗
PubMed2001

Molecular cloning of a new crystal protein gene cry1Af1 of Bacillus thuringiensis NT0423 from Korean sericultural farms.

A new cry1Ab-type gene encoding the 130 kDa protein of Bacillus thuringiensis NT0423 bipyramidal crystals was cloned, sequenced, and expressed in a crystal-negative B. thuringiensis host. Hybridization experiments revealed that the crystal protein gene is located on a 44 MDa plasmid of B. thuringiensis NT0423. A strong positive signal detected on the 6.6 kb HindIII fragment from B. thuringiensis NT0423 plasmid DNA was cloned and sequenced. The cry1Ab-type gene, designated cry1Af1, consisted of open reading frame of 3453 bp, encoding a protein of 1151 amino acid residues. The polypeptide has the deduced amino acid sequences predicting molecular masses of 130,215 Da. With both Bt I and Br II promoter sequences were found, the B. thuringiensis NT0423 crystal protein gene promoter closely aligned with those of cry1A-type crystal protein gene. When compared with known sequences of other Cry and Cyt proteins, the Cry1Af1 protein showed maximum 93% sequence identity to Cry1Ab protein of B. thuringiensis subsp. kurstaki. The expressed Cry1Af1 protein in a crystal-negative B. thuringiensis host appears to have strong insecticidal activity against lepidopteran larvae (Plutella xylostella). Crystals containing Cry1Af1 were about six times more toxic than the wild-type crystals of B. thuringiensis NT0423.

Agriculture↗
PubMed2002

Oxalate crystal deposition disease.

In addition to monosodium urate, calcium pyrophosphate dihydrate, and apatite crystals, oxalate crystals are less often found in synovial fluids in association with acute or chronic arthritis. Oxalate crystal deposition disease is seen in patients with primary hyperoxaluria types 1 and 2 (PH1 and 2) and in patients with end-stage renal disease managed with long-term dialysis. Oxalate crystal deposits are found mainly in kidneys, bone, skin, and vessels, and less often inside the joints. Musculoskeletal and systemic manifestations of oxalate crystal deposition disease may be confused with those observed with the other most common types of crystal deposition diseases. Clinical and radiographic features include calcium oxalate osteopathy, acute and chronic arthropathy with chondrocalcinosis, synovial calcification, and miliary skin calcium oxalate deposits and vascular calcifications that affect mainly the hands and feet. Systemic life-threatening cardiovascular, neurologic, and hematologic manifestations are rare. Genomic DNA studies have identified those genetic defects of PH1 and PH2 that allow a precise early diagnosis. Kidney transplantation has poor outcome as a result of graft oxalosis. Combined liver and kidney transplantation is the treatment of choice in patients with PH1 and advanced renal failure. Pre-emptive isolated liver transplantation is the preferred treatment in patients who develop the disease during infancy with progressive manifestations of oxalosis. These novel findings in the understanding of the molecular and enzymatic aspects of primary hyperoxalurias have provided a more rational basis for the management and prevention of oxalate crystal deposition disease. This information may lead to a better understanding and effective management of other common calcium-containing crystal deposition diseases.

Humans↗
PubMed1990

Sequential removal of Ca2+ from satellite tobacco necrosis virus. Crystal structure of two EDTA-treated forms.

Two forms of EDTA-treated satellite tobacco necrosis virus (STNV) have been studied with X-ray crystallography methods. The crystals of both forms were isomorphous with native STNV crystals, and (FEDTA-Fnat) maps as well as (2FEDTA-Fnat) maps were calculated with phases from the native structure. The maps were based on partial data sets to 2.8 A resolution, and averaged using the 60-fold non-crystallographic symmetry. In the first crystal form, calcium ions were absent from one of the three sites in the icosahedral protein shell. The crystals were produced at pH 5.0 from a virus solution treated with EDTA at pH 6.5. The virions were not expanded, and no essential changes were seen in the protein shell. In the second crystal form, all calcium ions in the protein shell were absent. The virus material in these crystals had been subjected to treatment with EDTA at pH 8.0 before crystallization at pH 6.5. The high pH treatment caused degradation of the viral RNA. No expansion of the virion had occurred and all protein--protein contacts were retained. These results are compared with the previously presented low-resolution structure of slightly expanded STNV with intact RNA, where calcium ions from two sites were absent. The relevance of Ca2(+)-depleted virions for infection in vivo is discussed as well as the possibility that the Ca2(+)-binding sites may be parts of ion channels in the viral capsid. One possible RNA-binding site was found in the maps of both crystal types, and the same site could also be localized in the high-resolution map of native STNV.

Calcium↗