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Results for “Solvent accessibility”

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PubMed1978

Hydrogen exchange kinetics of human hemoglobins. The pH dependence of solvent accessibility in cyanomet-, oxy-, and deoxyhemoglobin.

The hydrogen exchange kinetics of human oxy-, deoxy-, and cyanomethemoglobin have been measured as a function of pH by the tritium tracer method. At 5 degrees C and in phosphate buffer both liganded and unliganded forms of ferrohemoglobin exhibit deviations from the regular pH dependence of exchange that is characteristic of cyanomethemoglobin. In oxyhemoglobin, the deviation from the normal exchange pattern is centered at pH 7.4 and is in the direction of increased exchange or solvent accessibility. The effect in deoxyhemogloin, while occurring at the same pH and being of the same order of magnitude, is in the opposite direction, thus suggesting a pH-induced conformational transition leading to a less accessible structure. The width of these pH-induced deviations in solvent accessibility is approximately 1 pH unit in both cases. We propose a model in which specific interactions between charged groups in both froms of ferrohemoglobin account for these deviations.

Cyanides↗

PubMed1998

Accuracy of secondary structure and solvent accessibility predictions for a clostridial neurotoxin C-fragment.

Earlier studies used Rost and Sander's artificial neural network [(1993a), J. Mol. Biol. 232, 584-599] to predict the secondary structures [Lebeda and Olson (1994), Proteins 20, 293-300] and residue solvent accessibilities [Lebeda and Olson (1997), J. Protein Chem. 16, 607-618] of the clostridial neurotoxins. Because the X-ray crystal structure of the 50-kDa C-terminal half of the heavy chain of tetanus toxin was recently determined, this report evaluates the accuracy of these network-derived predictions. For this predominantly beta-strand-containing fragment, predictions, on a per-residue basis, for both secondary structure and solvent accessibility were about 70% accurate. A more flexible and realistic analysis based on overlapping segments yielded accuracies of over 80% for the three-state secondary structure and for the two-state accessibility predictions. Because the accuracies of these predictions are comparable to those made by Rost and Sander using a dataset of 126 nonhomologous globular proteins, our predictions provide a quantitative foundation for gauging the results when building by homology the structures of related proteins.

Botulinum Toxins↗

PubMed1987

Temperature-sensitive mutations of bacteriophage T4 lysozyme occur at sites with low mobility and low solvent accessibility in the folded protein.

Twenty-five different temperature-sensitive point mutations at 20 sites in the lysozyme gene of bacteriophage T4 have been identified. All of the mutations alter amino acid side chains that have lower than average crystallographic thermal factors and reduced solvent accessibility in the folded protein. This suggests that the amino acids with well-defined conformations can form specific intramolecular interactions that make relatively large contributions to the thermal stability of the protein. Residues with high mobility or high solvent accessibility are much less susceptible to destabilizing substitutions, suggesting that, in general, such amino acids contribute less to protein stability. The pattern of the sites of ts substitutions observed in the folded conformation of T4 lysozyme suggests that severe destabilizing mutations that primarily affect the free energy of the unfolded state are rare. These results indicate that proteins can be stabilized by adding new interactions to regions that are rigid or buried in the folded conformation.

2-Aminopurine↗

PubMed1985

The lack of a solvent accessible hydroxide or water ligand to iron at the 3Fe center of Azotobacter vinelandii ferredoxin I.

The X-ray crystal structure of Azotobacter vinelandii ferredoxin I (FdI) describes a planar 3Fe-3S center in which one of the iron atoms is ligated to a solvent accessible oxo ligand, presumably from water or hydroxide (Ghosh et al., (1982) J. Mol. Biol. 158, 73-109). Efforts to displace the proposed oxo ligand with cyanide were unsuccessful, even in 80% dimethylsulfoxide. In addition, comparison of the electron spin echo envelopes for H2O- and D2O-equilibrated samples of FdI showed only a slight deuterium modulation, far less than would be expected were water to be bound as an iron ligand. These results do not support the presence of a solvent accessible oxo ligand to the 3Fe center as described in the X-ray crystal structure.

Azotobacter↗

PubMed2006

Glycine-rich transmembrane helix 10 in the staphylococcal tetracycline transporter TetA(K) lines a solvent-accessible channel.

The staphylococcal TetA(K) tetracycline exporter is classified within the major facilitator superfamily of transport proteins and contains 14 alpha-helical transmembrane segments (TMS). Using cysteine-scanning mutagenesis, 27 amino acid residues across and flanking putative TMS 10 of the TetA(K) transporter were individually replaced with cysteine. The level of solvent accessibility to each of the targeted amino acid positions was determined as a measure of fluorescein maleimide reactivity and demonstrated that TMS 10 of TetA(K) has a cytoplasmic boundary at G313 and is likely to extend from at least V298 on the periplasmic side. TMS 10 was found to be amphiphilic containing at least partially solvent accessible amino acid residues along the length of one helical face, suggesting that this helix may line a solvent-exposed channel. Functional analyses of these cysteine mutants demonstrated a significant role for a number of amino acid residues, including a predominance of glycine residues which were further analyzed by alanine substitution. These residues are postulated to allow interhelical interactions between TMS 10 and distal parts of TetA(K) that are likely to be required for the tetracycline transport mechanism in TetA(K) and may be a general feature required by bacterial tetracycline transporters for activity.

Antiporters↗

PubMed2006

Following the dynamics of changes in solvent accessibility of 16 S and 23 S rRNA during ribosomal subunit association using synchrotron-generated hydroxyl radicals.

We have probed the structure and dynamics of ribosomal RNA in the Escherichia coli ribosome using equilibrium and time-resolved hydroxyl radical (OH) RNA footprinting to explore changes in the solvent-accessible surface of the rRNA with single-nucleotide resolution. The goal of these studies is to better understand the structural transitions that accompany association of the 30 S and 50 S subunits and to build a foundation for the quantitative analysis of ribosome structural dynamics during translation. Clear portraits of the subunit interface surfaces for 16 S and 23 S rRNA were obtained by constructing difference maps between the OH protection maps of the free subunits and that of the associated ribosome. In addition to inter-subunit contacts consistent with the crystal structure, additional OH protections are evident in regions at or near the subunit interface that reflect association-induced conformational changes. Comparison of these data with the comparable difference maps of the solvent-accessible surface of the rRNA calculated for the Thermus thermophilus X-ray crystal structures shows extensive agreement but also distinct differences. As a prelude to time-resolved OH footprinting studies, the reactivity profiles obtained using Fe(II)EDTA and X-ray generated OH were comprehensively compared. The reactivity patterns are similar except for a small number of nucleotides that have decreased reactivity to OH generated from Fe(II)EDTA compared to X-rays. These nucleotides are generally close to ribosomal proteins, which can quench diffusing radicals by virtue of side-chain oxidation. Synchrotron X-ray OH footprinting was used to monitor the kinetics of association of the 30 S and 50 S subunits. The rates individually measured for the inter-subunit contacts are comparable within experimental error. The application of this approach to the study of ribosome dynamics during the translation cycle is discussed.

Crystallography, X-Ray↗

PubMed2005

Relative importance of secondary structure and solvent accessibility to the stability of protein mutants. A case study with amino acid properties and energetics on T4 and human lysozymes.

Understanding the factors influencing the stability of protein mutants is an important task in molecular and computational biology. In this work, we have approached this problem by examining the relative importance of secondary structure and solvent accessibility of the mutant residue for understanding/predicting the stability of protein mutants. We have used hydrophobic, electrostatic and hydrogen bond free energy terms and nine unique physicochemical, energetic and conformational properties of amino acids in the present study and these parameters have been related with changes in thermal stability (DeltaTm) of all the single mutants of lysozymes based on single and multiple correlation coefficients. As expected the properties reflecting hydrophobicity and hydrophobic free energy play a major role to distinguish stabilizing and destabilizing mutants. The hydrophobic free energy due to carbon and nitrogen atoms distinguish the stability of coil and strand mutations to the accuracy of 100 and 90%, respectively. In agreement with previous results, the subgroup classification based on secondary structure and the information about its location in the structure yielded good relationship with the experimental DeltaTm. We revealed that the secondary structure information is equally or more important than solvent accessibility for understanding the stability of protein mutants. The comparison of amino acid properties with free-energy terms indicate that the energetic contribution explains the mutant stability better in coil region whereas the amino acid properties do better in strand region. Further, the combination of free energies with amino acid properties increased the correlation significantly. The present study demonstrates the importance of classifying the mutants based on secondary structure to the stability of proteins upon mutations.

Amino Acids↗

PubMed2004

Latency and substrate binding globally reduce solvent accessibility of plasminogen activator inhibitor type 1 (PAI-1). An adaptation of PAI-1 conformer crystal structures by hydrogen-deuterium exchange.

Plasminogen activator inhibitor type 1 (PAI-1) plays key regulatory roles in fibrinolysis, cell migration, and tissue remodeling. A regulatory protein without known catalytic activity, PAI-1 modulates plasminogen activators through protein-protein interactions. Although global conformational alterations that occur in PAI-1 determine its regulatory activity, comprehensive assessments of concurrent dynamic, structural, and functional alterations of this critical regulatory protein have not yet been clearly defined. X-ray crystallographic studies have described four distinct PAI-1 conformational states: active, latent, reactive center loop peptide-annealed (RCL-PA), and cleaved mutant. In this study, backbone amide hydrogen-deuterium exchange detected by mass spectrometry was used to characterize dynamic and structural alterations of human PAI-1 (hPAI-1) in relation to its function. hPAI-1 conformers were defined by surface mapping the solvent-accessible sites for strategic secondary structural components of the protein. We observed a global protection from solvent for a majority of peptides in the latent conformer relative to the active conformer. Significant differences were observed in the RCL, helix A, helix D, and sheet 1C, and these regions were markedly more dynamic or solvent-exposed in the active conformation. The RCL-PA form adopts an intermediate conformational state between the active and the latent conformers. Our results demonstrate that the most dynamic regions of PAI-1 (the RCL, helices D and A, and sheet 5A) are flexible in the transition toward latency. They also show that the dynamic surface structures of the active, latent, and peptide-annealed conformers of PAI-1 are underestimated by theoretical solvent accessibility calculations derived from crystallographic data.

Amino Acid Sequence↗

PubMed2006

Solvent accessibility of protein surfaces by amide H/2H exchange MALDI-TOF mass spectrometry.

One advantage of detecting amide H/2H exchange by mass spectrometry instead of NMR is that the more rapidly exchanging surface amides are still detectable. In this study, we present quench-flow amide H/2H exchange experiments to probe how rapidly the surfaces of two different proteins exchange. We compared the amide H/2H exchange behavior of thrombin, a globular protein, and IkappaBalpha, a nonglobular protein, to explore any differences in the determinants of amide H/2H exchange rates for each class of protein. The rates of exchange of only a few of the surface amides were as rapid as the "intrinsic" exchange rates measured for amides in unstructured peptides. Most of the surface amides exchanged at a slower rate, despite the fact that they were not seen to be hydrogen bonded to another protein group in the crystal structure. To elucidate the influence of the surface environment on amide H/2H exchange, we compared exchange data with the number of amides participating in hydrogen bonds with other protein groups and with the solvent accessible surface area. The best correlation with amide H/2H exchange was found with the total solvent accessible surface area, including side chains. In the case of the globular protein, the correlation was modest, whereas it was well correlated for the nonglobular protein. The nonglobular protein also showed a correlation between amide exchange and hydrogen bonding. These data suggest that other factors, such as complex dynamic behavior and surface burial, may alter the expected exchange rates in globular proteins more than in nonglobular proteins where all of the residues are near the surface.

Amides↗

PubMed2005

Combining prediction of secondary structure and solvent accessibility in proteins.

Owing to the use of evolutionary information and advanced machine learning protocols, secondary structures of amino acid residues in proteins can be predicted from the primary sequence with more than 75% per-residue accuracy for the 3-state (i.e., helix, beta-strand, and coil) classification problem. In this work we investigate whether further progress may be achieved by incorporating the relative solvent accessibility (RSA) of an amino acid residue as a fingerprint of the overall topology of the protein. Toward that goal, we developed a novel method for secondary structure prediction that uses predicted RSA in addition to attributes derived from evolutionary profiles. Our general approach follows the 2-stage protocol of Rost and Sander, with a number of Elman-type recurrent neural networks (NNs) combined into a consensus predictor. The RSA is predicted using our recently developed regression-based method that provides real-valued RSA, with the overall correlation coefficients between the actual and predicted RSA of about 0.66 in rigorous tests on independent control sets. Using the predicted RSA, we were able to improve the performance of our secondary structure prediction by up to 1.4% and achieved the overall per-residue accuracy between 77.0% and 78.4% for the 3-state classification problem on different control sets comprising, together, 603 proteins without homology to proteins included in the training. The effects of including solvent accessibility depend on the quality of RSA prediction. In the limit of perfect prediction (i.e., when using the actual RSA values derived from known protein structures), the accuracy of secondary structure prediction increases by up to 4%. We also observed that projecting real-valued RSA into 2 discrete classes with the commonly used threshold of 25% RSA decreases the classification accuracy for secondary structure prediction. While the level of improvement of secondary structure prediction may be different for prediction protocols that implicitly account for RSA in other ways, we conclude that an increase in the 3-state classification accuracy may be achieved when combining RSA with a state-of-the-art protocol utilizing evolutionary profiles. The new method is available through a Web server at http://sable.cchmc.org.

Amino Acid Sequence↗

PubMed1998

Pairwise calculation of protein solvent-accessible surface areas.

BACKGROUND: The tractability of many algorithms for determining the energy state of a system depends on the pairwise nature of an energy expression. Some energy terms, such as the standard implementation of the van der Waals potential, satisfy this criterion whereas others do not. One class of important potentials that are not pairwise involves benefits and penalties for burying hydrophobic and/or polar surface areas. It has been found previously that, in some cases, a pairwise approximation to these surface areas correlates with the true surface areas. We set out to generalize the applicability of this approximation. RESULTS: We develop a pairwise expression with one scalable parameter that closely reproduces both the true buried and the true exposed solvent-accessible surface areas. We then refit our previously published coiled-coil stability data to give solvation parameters of 26 cal/mol A2 favoring hydrophobic burial and 100 cal/mol A2 opposing polar burial. CONCLUSIONS: An accurate pairwise approximation to calculate exposed and buried protein solvent-accessible surface area is achieved.

Algorithms↗

PubMed2003

Solvent accessible surface area (ASA) of simulated phospholipid membranes.

The membrane-solvent interface has been investigated through calculations of the solvent accessible surface area (ASA) for simulated membranes of DPPC and POPE. For DPPC at 52 degrees C we found an ASA of 126+/-8 A(2) per lipid molecule, equivalent to twice the projected lateral area. The ASA was dominated by the contribution from the quaternary ammonium ion which accounts for about two thirds of the total value. The remaining ASA is primarily the phosphate moiety (22+/-1 A(2)), and this contribution almost entirely represents the two 'out-of-chain' oxygen atoms. Interestingly, even the most exposed parts of the PC head-group show average ASAs of less than half of its maximal or 'fully hydrated' value. The average ASA of a simulated POPE membrane was 96+/-7 A(2) per lipid. The smaller value than for DPPC reflects much lower ASA of the ammonium ion, which is partially compensated by increased exposure of the ethylene and phosphate moieties. The ASA of the polar moieties of (PO(4), NH(3) and COO) constitutes 65% of the total accessible area for POPE, making this interface more polar than that of DPPC. It is suggested that ASA information can be valuable in attempts to rationalize experimental investigations, particularly molecular interpretations of thermodynamic information.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2002

Enhancing oxidative resistance of Agrobacterium radiobacter N-carbamoyl D-amino acid amidohydrolase by engineering solvent-accessible methionine residues.

N-Carbamoyl D-amino acid amidohydrolase (D-NCAase) that catalyzes the stereospecific hydrolysis of N-carbamoyl D-amino acids to their corresponding D-amino acids is valuable in pharmaceutical industry. Agrobacterium radiobacter D-NCAase is sensitive to oxidative damage by hydrogen peroxide. To investigate the role of methionine residues in oxidative inactivation, each of the nine methionine residues in A. radiobacter D-NCAase was substituted with leucine, respectively, by site-directed mutagenesis. Except for two mutants (Met5Leu and Met31Leu) with similar activities, seven mutants (Met73Leu, Met167Leu/Met169Leu, Met184Leu, Met220Leu, Met239Leu, Met244Leu, and Met239Leu/Met244Leu) were found to have reduced activities. In the presence of H(2)O(2), three mutants (Met239Leu, Met244Leu, and Met239Leu/Met244Leu) with substitution of highly solvent-accessible methionines by leucines retained their activities. The other mutants were also considerably resistant to chemical oxidation than was the wild-type enzyme. Thus, substitution of solvent-accessible methionine residues with leucine to enhance oxidative stability of D-NCAase is practical but might be with compromised activity.

Amidohydrolases↗

PubMed2004

Accurate prediction of solvent accessibility using neural networks-based regression.

Accurate prediction of relative solvent accessibilities (RSAs) of amino acid residues in proteins may be used to facilitate protein structure prediction and functional annotation. Toward that goal we developed a novel method for improved prediction of RSAs. Contrary to other machine learning-based methods from the literature, we do not impose a classification problem with arbitrary boundaries between the classes. Instead, we seek a continuous approximation of the real-value RSA using nonlinear regression, with several feed forward and recurrent neural networks, which are then combined into a consensus predictor. A set of 860 protein structures derived from the PFAM database was used for training, whereas validation of the results was carefully performed on several nonredundant control sets comprising a total of 603 structures derived from new Protein Data Bank structures and had no homology to proteins included in the training. Two classes of alternative predictors were developed for comparison with the regression-based approach: one based on the standard classification approach and the other based on a semicontinuous approximation with the so-called thermometer encoding. Furthermore, a weighted approximation, with errors being scaled by the observed levels of variability in RSA for equivalent residues in families of homologous structures, was applied in order to improve the results. The effects of including evolutionary profiles and the growth of sequence databases were assessed. In accord with the observed levels of variability in RSA for different ranges of RSA values, the regression accuracy is higher for buried than for exposed residues, with overall 15.3-15.8% mean absolute errors and correlation coefficients between the predicted and experimental values of 0.64-0.67 on different control sets. The new method outperforms classification-based algorithms when the real value predictions are projected onto two-class classification problems with several commonly used thresholds to separate exposed and buried residues. For example, classification accuracy of about 77% is consistently achieved on all control sets with a threshold of 25% RSA. A web server that enables RSA prediction using the new method and provides customizable graphical representation of the results is available at http://sable.cchmc.org.

Artificial Intelligence↗

PubMed2002

Positioning of anchor groups in protein loop prediction: the importance of solvent accessibility and secondary structure elements.

The prediction of loop regions in the process of protein structure prediction by homology is still an unsolved problem. In an earlier publication, we could show that the correct placement of the amino acids serving as an anchor group to be connected by a loop fragment with a predicted geometry is a highly important step and an essential requirement within the process (Lessel and Schomburg, Proteins 1999; 37:56-64). In this article, we present an analysis of the quality of possible loop predictions with respect to gap length, fragment length, amino acid type, secondary structure, and solvent accessibility. For 550 insertions and 544 deletions, we test all possible positions for anchor groups with an inserted loop of a length between 3 and 12 amino acids. We could show that approximately 80% of the indel regions could be predicted within 1.5 A RMSD from a knowledge-based loop data base if criteria for the correct localization of anchor groups could be found and the loops can be sorted correctly. From our analysis, several conclusions regarding the optimal placement of anchor groups become obvious: (1) The correct placement of anchor groups is even more important for longer gap lengths, (2) medium length fragments (length 5-8) perform better than short or long ones, (3) the placement of anchor groups at hydrophobic amino acids gives a higher chance to include the best possible loop, (4) anchor groups within secondary structure elements, in particular beta-sheets are suitable, (5) amino acids with lower solvent accessibility are better anchor group. A preliminary test using a combination of the anchor group positioning criteria deduced from our analysis shows very promising results.

Algorithms↗

PubMed1998

A set of van der Waals and coulombic radii of protein atoms for molecular and solvent-accessible surface calculation, packing evaluation, and docking.

We analyze the contact distance distributions between nonbonded atoms in known protein structures. A complete set of van der Waals (VDW) radii for 24 protein atom types and for crystal-bound water is derived from the contact distance distributions of these atoms with a selected group of apolar atoms. In addition, a set of Coulombic radii for polar atoms is derived from their contacts with water. The contact distance distributions and the two sets of radii are derived in a systematic and self-consistent manner using an iterative procedure. The Coulombic radii for polar atoms are, on average, 0.18 A smaller than their VDW radii. The VDW radius of water is 1.7 A, which is 0.3 A larger than its Coulombic radius. We show that both the VDW and the Coulombic radii of polar atoms are needed in calculating the molecular and solvent-accessible surfaces of proteins. The VDW radii are needed to generate the apolar portions of the surface and the Coulombic radii for the polar portions. The fact that polar atoms have two apparent sizes implies that a hydrophobic cavity has to be larger than a polar cavity in order to accommodate the same number of water molecules. Most surface area calculations have used only one radius for each polar atom. As a result, unreal cavities, grooves, or pockets may be generated if the Coulombic radii of polar atoms are used. On the other hand, if the VDW radii of polar atoms are used, the details of the polar regions of the surface may be lost. The accuracy of the molecular and the solvent-accessible surfaces of proteins can be improved if the radii of polar atoms are allowed to change depending on the nature of their contacting neighbors. The surface of a protein at a protein-protein interface differs from that in solution in that it has to be generated using at least two kinds of probes, one representing a typical apolar atom and the other a typical polar atom. This observation has important implications for docking, which relies on surface complementarity at the interface.

Evaluation Studies as Topic↗

PubMed1989

Quantitative analysis of DNA secondary structure from solvent-accessible surfaces: the B- to Z-DNA transition as a model.

Solvent structure and its interactions have been suggested to play a critical role in defining the conformation of polynucleotides and other macromolecules. In this work, we attempt to quantitate solvent effects on the well-studied conformational transition between right-handed B- and left-handed Z-DNA. The solvent-accessible surfaces of the hexamer sequences d(m5CG)3, d(CG)3, d(CA)3, and d(TA)3 were calculated in their B- and Z-DNA conformations. The difference in hydration free energies between the Z and the B conformations (delta delta GH(Z-B] was determined from these surfaces to be -0.494 kcal/mol for C-5 methylated d(CG), 0.228 kcal/mol for unmethylated d(CG), 0.756 kcal/mol for d(CA)-d(TG), and 0.896 kcal/mol for d(TA) dinucleotides. These delta delta GH(Z-B) values were compared to the experimental B- to Z-DNA transition energies of -0.56 kcal/mol that we measured for C-5 methylated d(CG), 0.69-1.30 kcal/mol reported for unmethylated d(CG), 1.32-1.48 kcal/mol reported for d(CA)-d(TG), and 2.3-2.4 kcal/mol for d(TA) dinucleotides. From this comparison, we found that the calculated delta delta GH(Z-B) of these dinucleotides could account for the previous observation that the dinucleotides were ordered as d(m5CG) greater than d(CG) greater than d(CA)-d(TG) greater than d(TA) in stability as Z-DNA. Furthermore, we predicted that one of the primary reasons for the inability of d(TA) sequences to form Z-DNA results from a decrease in exposed hydrophilic surfaces of adjacent base pairs due to the C-5 methyl group of thymine; thus, d(UA) dinucleotides should be more stable as Z-DNA than the analogous d(TA) dinucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA↗

PubMed1977

Solvent accessibilities in glycyl, alanyl and seryl dipeptides.

Theoretical studies on glycyl-alanyl and seryl dipeptides were performed to determine the probable backbone and side-group conformations that are preferred for solvent interaction. By following the method of Lee & Richards [(1971) J. Mol. Biol. 55, 379-400], a solute molecule is represented by a set of interlocking spheres of appropriate van der Waals radii assigned to each atom, and a solvent (water) molecule is rolled along the envelope of the van der Waals surface, and the surface accessible to the solvent molecule, and hence the solvent accessibility for a particular conformation of the solute molecule, is computed. From the calculated solvent accessibilities for various conformations, solvation maps for dipeptides were constructed. These solvation maps suggest that the backbone polar atoms could interact with solvent molecules selectively, depending on the backbone conformation. A conformation in the right-handed bridge (zetaR) region is favoured for both solvent interaction and intrachain hydrogen-bonding. Also the backbone side-chain hydrogen-bonding within the same dipeptide fragment in proteins is less favoured than hydrogen-bonding between side chain and water and between side chain and atoms of other residues. Solvent accessibilities suggest that very short distorted alphaR-helical and extended-structural parts may be stabilized via solvent interaction, and this could easily be possible at the surface of the protein molecules, in agreement with protein-crystal data.

Alanine↗