Biomedical subjects

Andrea Mozzarelli

Publications and source records attributed to Andrea Mozzarelli.

At least 37 records · Page 2Linked to original sources

PubMed2004

Spectroscopic and functional characterization of T state hemoglobin conformations encapsulated in silica gels.

Oxygen binding curves of sol-gel-encapsulated deoxy human adult hemoglobin (HbA) have previously revealed two distinct noncooperative populations with oxygen binding affinities approximately 1000 and 100 times lower than that of the high-affinity R state. The two populations which have been termed the low-affinity (LA) and high-affinity (HA) T states can be selectively stabilized using two different encapsulation protocols for deoxy-HbA. The present study seeks to understand the factors giving rise to these different affinity states. Visible and UV resonance Raman spectroscopies are used to characterize the conformational properties of both the deoxy and deoxy-turned-carbonmonoxy (CO) derivatives of HbA derived from the two encapsulation protocols. The geminate and bimolecular recombination of CO to the photodissociated CO derivatives is used to characterize the functional properties of the slowly evolving encapsulated populations. The results show that the initial deoxy-HbA populations are conformationally indistinguishable with respect to encapsulation protocol. The addition of CO to sol-gel-encapsulated deoxy-HbA triggers a detectable progression of conformational and functional changes. Visible resonance Raman spectra of the CO photoproduct reveal a progression of changes of the iron-proximal histidine stretching frequencies: 215, 222, 227, and 230 cm(-1). The low and high values correspond to the initial deoxy T state and liganded R (R(2)) state species, respectively. The 222 and 227 cm(-1) species are generated using encapsulation protocols that give rise to what are termed the LA and HA T states, respectively. The UV resonance Raman spectra of these and related species indicate that the progression from deoxy T to LA to HA is associated with a progressive loosening of T state constraints within the hinge and switch regions of the alpha(1)beta(2) interface. The time scale for the progression is determined by a balance between the ligation-initiated evolution toward high-affinity conformations and factors such as allosteric effectors, gel matrix, and added glycerol that slow ligand-binding-induced relaxation. Thus, it appears that the encapsulation protocol-dependent rate of ligand-binding-induced relaxation determines the functional properties of the initially encapsulated deoxy-HbA population.

Adult↗

PubMed2004

Computational titration analysis of a multiprotic HIV-1 protease-ligand complex.

A new computational method for analyzing the protonation states of protein-ligand complexes with multiple ionizable groups is applied to the structurally characterized complex between the peptide Glu-Asp-Leu and HIV-1 protease. This complex has eight ionizable groups at the active site: four from the ligand and four Asp residues on the protein. Correlation, with an error of ca. 0.6 kcal mol-1, is made between the calculated titration curve and the experimental titration curve. The analysis suggests that between four and five of the eight ionizable groups are protonated at the pH of crystallization.

Binding Sites↗

PubMed2004

New insights into allosteric mechanisms from trapping unstable protein conformations in silica gels.

To understand why the classical two-state allosteric model of Monod, Wyman, and Changeux explains cooperative oxygen binding by hemoglobin but does not explain changes in oxygen affinity by allosteric inhibitors, we have investigated the kinetic properties of unstable conformations transiently trapped by encapsulation in silica gels. Conformational trapping reveals that after nanosecond photodissociation of carbon monoxide a large fraction of the subunits of the T quaternary structure has kinetic properties almost identical to those of subunits of the R quaternary structure. Addition of allosteric inhibitors reduces both the fraction of R-like subunits and the oxygen affinity of the T quaternary structure. These kinetic and equilibrium results are readily explained by a recently proposed generalization of the Monod-Wyman-Changeux model in which a pre-equilibrium between two functionally different tertiary, rather than quaternary, conformations plays the central role.

Allosteric Regulation↗

PubMed2004

Simple, intuitive calculations of free energy of binding for protein-ligand complexes. 3. The free energy contribution of structural water molecules in HIV-1 protease complexes.

Structural water molecules within protein active sites are relevant for ligand-protein recognition because they modify the active site geometry and contribute to binding affinity. In this work an analysis of the interactions between 23 ligands and dimeric HIV-1 protease is reported. The X-ray structures of these complexes show the presence of four types of structural water molecules: water 301 (on the symmetry axis), water 313, water 313bis, and peripheral waters. Except for water 301, these are generally complemented with a symmetry-related set. The GRID program was used both for checking water locations and for placing water molecules that appear to be missing from the complexes due to crystallographic uncertainty. Hydropathic analysis of the energetic contributions using HINT indicates a significant improvement of the correlation between HINT scores and the experimentally determined binding constants when the appropriate bridging water molecules are taken into account. In the absence of water r2 = 0.30 with a standard error of +/- 1.30 kcal mol(-1) and when the energetic contributions of the constrained waters are included r2 = 0.61 with a standard error of +/- 0.98 kcal mol(-1). HINT was shown to be able to map quantitatively the contribution of individual structural waters to binding energy. The order of relevance for the various types of water is water 301 > water 313 > water 313bis > peripheral waters. Thus, to obtain the most reliable free energy predictions, the contributions of structural water molecules should be included. However, care must be taken to include the effects of water molecules that add information value and not just noise.

Binding Sites↗

PubMed2004

pH dependence of tryptophan synthase catalytic mechanism: I. The first stage, the beta-elimination reaction.

The pyridoxal 5'-phosphate-dependent beta-subunit of the tryptophan synthase alpha(2)beta(2) complex catalyzes the condensation of L-serine with indole to form L-tryptophan. The first stage of the reaction is a beta-elimination that involves a very fast interconversion of the internal aldimine in a highly fluorescent L-serine external aldimine that decays, via the alpha-carbon proton removal and beta-hydroxyl group release, to the alpha-aminoacrylate Schiff base. This reaction is influenced by protons, monovalent cations, and alpha-subunit ligands that modulate the distribution between open and closed conformations. In order to identify the ionizable residues that might assist catalysis, we have investigated the pH dependence of the rate of the external aldimine decay by rapid scanning UV-visible absorption and single wavelength fluorescence stopped flow. In the pH range 6-9, the reaction was found to be biphasic with the first phase (rate constants k(1)) accounting for more than 70% of the signal change. In the absence of monovalent cations or in the presence of sodium and potassium ions, the pH dependence of k(1) exhibits a bell shaped profile characterized by a pK(a1) of about 6 and a pK(a2) of about 9, whereas in the presence of cesium ions, the pH dependence exhibits a saturation profile characterized by a single pK(a) of 9. The presence of the allosteric effector indole acetylglycine increases the rate of reaction without altering the pH profile and pK(a) values. By combining structural information for the internal aldimine, the external aldimine, and the alpha-aminoacrylate with kinetic data on the wild type enzyme and beta-active site mutants, we have tentatively assigned pK(a1) to betaAsp-305 and pK(a2) to betaLys-87. The loss of pK(a1) in the presence of cesium ions might be due to a shift to lower values, caused by the selective stabilization of a closed form of the beta-subunit.

Bacterial Proteins↗

PubMed2004

Getting it right: modeling of pH, solvent and "nearly" everything else in virtual screening of biological targets.

"Getting it right" refers to the careful modeling of all elements in the living system, i.e. biological macromolecules, ligands and water molecules. In addition, careful attention should be paid to the protonation state of ionizable functional groups on the ligands and residues at the active site. Computational technology based on the empirical HINT program is described to: (1) calculate free energy scores for ligand binding; (2) include the implicit and explicit effects of water in and around the ligand binding site; and (3) incorporate the effects of global and local pH in molecular models. This last point argues for the simultaneous consideration of a number of molecular models, each with different protonation profiles. Data from recent studies of protein-ligand systems (trypsin, thrombin, neuraminidase, HIV-1 protease and others) are used to illustrate the concepts in the paper. Also discussed are experimental factors related to accurate free energy predictions with this and other computational technologies.

Benzylamines↗

PubMed2004

Microspectrophotometry for structural enzymology.

For several decades, single-crystal microspectrophotometry has contributed to structural enzymology as a very useful complement to X-ray crystallography. In its most recent applications, it is the ideal tool to track chemistry as structure evolves in the course of time-resolved experiments, to identify freeze-trapped catalytic intermediates and to assess radiation-induced effects on enzyme crystals. To these goals, instruments have been developed to record optical spectra 'on-line' in the course of X-ray data collection, whereas more rigorous polarized absorption studies 'off-line' play an essential role in describing what protein function is retained in the crystalline state and correlating it with the observed structures.

Animals↗

PubMed2004

Tyrosine phenol-lyase and tryptophan indole-lyase encapsulated in wet nanoporous silica gels: Selective stabilization of tertiary conformations.

The pyridoxal 5'-phosphate-dependent enzymes tyrosine phenol-lyase and tryptophan indole-lyase were encapsulated in wet nanoporous silica gels, a powerful method to selectively stabilize tertiary and quaternary protein conformations and to develop bioreactors and biosensors. A comparison of the enzyme reactivity in silica gels and in solution was carried out by determining equilibrium and kinetic parameters, exploiting the distinct spectral properties of catalytic intermediates and reaction products. The encapsulated enzymes exhibit altered distributions of ketoenamine and enolimine tautomers, increased values of inhibitors dissociation constants, slow attaining of steady-state in the presence of substrate and substrate analogs, modified steady-state distribution of catalytic intermediates, and a sixfold-eightfold decrease of specific activities. This behavior can be rationalized by a reduced conformational flexibility for the encapsulated enzymes and a selective stabilization of either the open (inactive) or the closed (active) form of the enzymes. Despite very similar structures and catalytic mechanisms, the influence of encapsulation is more pronounced for tyrosine phenol-lyase than tryptophan indole-lyase. This finding indicates that subtle structural and dynamic differences can lead to distinct interactions of the protein with the gel matrix.

Bacterial Proteins↗

PubMed2004

Free energy of ligand binding to protein: evaluation of the contribution of water molecules by computational methods.

One of the more challenging issues in medicinal chemistry is the computation of the free energy of ligand binding to macromolecular targets. This allows for the screening of libraries of chemicals for fast and inexpensive identification of lead compounds. Many attempts have been made and several algorithms have been developed for this purpose. Whereas enthalpic contributions are evaluated using methods and equations for which there is a reasonable consensus among researchers, the entropic contribution is evaluated using very different, and, in some cases, very approximate methods, or it is entirely ignored. Entropic contributions are of primary importance in the formation of many ligand-protein complexes, as well as in protein folding. The hydrophobic interaction, associated with the release of water molecules from the protein active site and the ligand, plays a significant role in complex formation, predominantly contributing to the total entropy change and, in some cases, to the total free energy of binding. There are distinct approaches for the evaluation of the contribution of water molecules to the free energy of binding based on Newtonian mechanics force fields, multi-parameter empirical scoring functions and experimental force fields. This review describes these methods -- discussing both their advantages and limitations. Particular emphasis will be placed on HINT (Hydropatic INTeractions), a "natural" force field that takes into account in a unified way enthalpic and entropic contributions of all interacting atoms in protein-ligand complexes, including released and structured water molecules. As a case-study, the contribution of water molecules to the binding free energy of HIV-1 protease inhibitors is evaluated.

Animals↗

PubMed2003

Simple, intuitive calculations of free energy of binding for protein-ligand complexes. 2. Computational titration and pH effects in molecular models of neuraminidase-inhibitor complexes.

One factor that can strongly influence predicted free energy of binding is the ionization state of functional groups on the ligands and at the binding site at which calculations are performed. This analysis is seldom performed except in very detailed computational simulations. In this work, we address the issues of (i) modeling the complexity resulting from the different ionization states of ligand and protein residues involved in binding, (ii) if, and how, computational methods can evaluate the pH dependence of ligand inhibition constants, and (iii) how to score the protonation-dependent models. We developed a new and fairly rapid protocol called "computational titration" that enables parallel modeling of multiple ionization ensembles for each distinct protonation level. Models for possible protonation combinations for site/ligand ionizable groups are built, and the free energy of interaction for each of them is quantified by the HINT (Hydropathic INTeractions) software. We applied this procedure to the evaluation of the binding affinity of nine inhibitors (six derived from 2,3-didehydro-2-deoxy-N-acetylneuraminic acid, DANA) of influenza virus neuraminidase (NA), a surface glycoprotein essential for virus replication and thus a pharmaceutically relevant target for the design of anti-influenza drugs. The three-dimensional structures of the NA enzyme-inhibitor complexes indicate considerable complexity as the ligand-protein recognition site contains several ionizable moieties. Each computational titration experiment reveals a peak HINT score as a function of added protons. This maximum HINT score indicates the optimum pH (or the optimum protonation state of each inhibitor-protein binding site) for binding. The pH at which inhibition is measured and/or crystals were grown and analyzed can vary from this optimum. A protonation model is proposed for each ligand that reconciles the experimental complex structure with measured inhibition and the free energy of binding. Computational titration methods allow us to analyze the effect of pH in silico and may be helpful in improving ligand binding free energy prediction when protonation or deprotonation of the residues or ligand functional groups at the binding site might be significant.

Algorithms↗

PubMed2003

Structures of gamma-aminobutyric acid (GABA) aminotransferase, a pyridoxal 5'-phosphate, and [2Fe-2S] cluster-containing enzyme, complexed with gamma-ethynyl-GABA and with the antiepilepsy drug vigabatrin.

Gamma-aminobutyric acid aminotransferase (GABA-AT) is a pyridoxal 5'-phosphate-dependent enzyme responsible for the degradation of the inhibitory neurotransmitter GABA. GABA-AT is a validated target for antiepilepsy drugs because its selective inhibition raises GABA concentrations in brain. The antiepilepsy drug, gamma-vinyl-GABA (vigabatrin) has been investigated in the past by various biochemical methods and resulted in several proposals for its mechanisms of inactivation. In this study we solved and compared the crystal structures of pig liver GABA-AT in its native form (to 2.3-A resolution) and in complex with vigabatrin as well as with the close analogue gamma-ethynyl-GABA (to 2.3 and 2.8 A, respectively). Both inactivators form a covalent ternary adduct with the active site Lys-329 and the pyridoxal 5'-phosphate (PLP) cofactor. The crystal structures provide direct support for specific inactivation mechanisms proposed earlier on the basis of radio-labeling experiments. The reactivity of GABA-AT crystals with the two GABA analogues was also investigated by polarized absorption microspectrophotometry. The spectral data are discussed in relation to the proposed mechanism. Intriguingly, all three structures revealed a [2Fe-2S] cluster of yet unknown function at the center of the dimeric molecule in the vicinity of the PLP cofactors.

4-Aminobutyrate Transaminase↗

PubMed2003

Role of aspartate-133 and histidine-458 in the mechanism of tryptophan indole-lyase from Proteus vulgaris.

Tryptophan indole-lyase (Trpase) from Proteus vulgaris is a pyridoxal 5'-phosphate dependent enzyme that catalyzes the reversible hydrolytic cleavage of L-Trp to yield indole and ammonium pyruvate. Asp-133 and His-458 are strictly conserved in all sequences of Trpase, and they are located in the proposed substrate-binding region of Trpase. These residues were mutated to alanine to probe their role in substrate binding and catalysis. D133A mutant Trpase has no measurable activity with L-Trp as substrate, but still retains activity with S-(o-nitrophenyl)-L-cysteine, S-alkyl-L-cysteines, and beta-chloro-L-alanine. H458A mutant Trpase has 1.6% of wild-type Trpase activity with L-Trp, and high activity with S-(o-nitrophenyl)-L-cysteine, S-alkyl-L-cysteines, and beta-chloro-L-alanine. H458A mutant Trpase does not exhibit the pK(a) of 5.3 seen in the pH dependence of k(cat)/K(m) of L-Trp for wild-type Trpase. Both mutant enzymes are inhibited by L-Ala, L-Met, and L-Phe, with K(i) values similar to those of wild-type Trpase, but oxindolyl-L-alanine and beta-phenyl-DL-serine show much weaker binding to the mutant enzymes, suggesting that Asp-133 and His-458 are involved in the binding of these ligands. D133A and H458A mutant Trpase exhibit absorption and CD spectra in the presence of substrates and inhibitors that are similar to wild-type Trpase, with peaks at about 420 and 500 nm. The rate constants for formation of the 500 nm bands for the mutant enzymes are equal to or greater than those of wild-type Trpase, indicating that Asp-133 and His-458 do not play a role in the formation of quinonoid intermediates. In constrast to wild-type and H458A mutant Trpase, D133A mutant Trpase forms an intermediate from S-ethyl-L-Cys that absorbs at 345 nm, and is likely to be an alpha-aminoacrylate. Crystals of D133A and H458A mutant Trpase bind amino acids with similar affinity as the proteins in solution, except for L-Ala, which binds to D133A mutant Trpase crystals about 20-fold stronger than in solution. These results suggest that Asp-133 and His-458 play an important role in the elimination reaction of L-Trp. Asp-133 likely forms a hydrogen bond directly to the indole NH of the substrate, while His-458 probably is hydrogen bonded to Asp-133.

Amino Acid Sequence↗

PubMed2003

Functional and spectroscopic characterization of half-liganded iron-zinc hybrid hemoglobin: evidence for conformational plasticity within the T state.

Functionally distinct conformations of HbA (human adult hemoglobin) were probed using deoxy and diliganded derivatives of symmetric Fe-Zn hybrids of HbA. To expand the range of accessible structures, different environments were utilized including solution, sol-gel encapsulation, and crystals. Further structural and functional modulation was achieved by the addition of allosteric effectors. Functional characterization included oxygen affinity measurements, CO combination rates, and geminate and bimolecular CO recombination, after photodissociation. The conformational properties were studied using visible resonance Raman spectroscopy as a probe of local tertiary structure at the iron-containing hemes and UV resonance Raman spectroscopy as a probe of elements of the globin known to be sensitive to quaternary structure. The combined results show a pattern in which there is a progression of conformational and functional properties that are consistent with a picture in which the T quaternary structure can accommodate a range of tertiary conformations (plasticity). At one end of the distribution is the equilibrium deoxy T state conformation that has the lowest ligand reactivity. At the other end of the distribution are T state conformations with higher ligand reactivity that exhibit "loosened" T state constraints within the globin including the alpha(1)beta(2) interface and reduced proximal strain at the heme.

Hemoglobins↗

PubMed2003

Surface-exposed tryptophan residues are essential for O-acetylserine sulfhydrylase structure, function, and stability.

O-Acetylserine sulfhydrylase is a homodimeric enzyme catalyzing the last step of cysteine biosynthesis via a Bi Bi ping-pong mechanism. The subunit is composed of two domains, each containing one tryptophan residue, Trp50 in the N-terminal domain and Trp161 in the C-terminal domain. Only Trp161 is highly conserved in eucaryotes and bacteria. The coenzyme pyridoxal 5'-phosphate is bound in a cleft between the two domains. The enzyme undergoes an open to closed conformational transition upon substrate binding. The effect of single Trp to Tyr mutations on O-acetylserine sulfhydrylase structure, function, and stability was investigated with a variety of spectroscopic techniques. The mutations do not significantly alter the enzyme secondary structure but affect the catalysis, with a predominant influence on the second half reaction. The W50Y mutation strongly affects the unfolding pathway due to the destabilization of the intersubunit interface. The W161Y mutation, occurring in the C-terminal domain, produces a reduction of the accessibility of the active site to acrylamide and stabilizes thermodynamically the N-terminal domain, a result consistent with stronger interdomain interactions.

Acrylamide↗

PubMed2003

The molecular pathway for the allosteric regulation of tryptophan synthase.

The pyridoxal 5'-phosphate (PLP)-dependent tryptophan synthase is a alpha(2)beta(2) complex. The alpha-beta subunit interaction plays a critical role both in the reciprocal activation of the individual subunits and in the allosteric regulation. We have investigated whether mutations of alpha loop6 Gly(181) and beta helix6 Ser(178) affect intersubunit communication. The loss of the hydrogen bond between these residues, achieved by proline substitution, does not significantly influence the intersubunit catalytic activation, but completely abolishes ligand-induced intersubunit signaling. The comparison of the crystal structure of the wild type and beta Ser(178)Pro mutant, in the absence and presence of alpha-subunit ligands, indicates that the removal of the interaction between beta Ser(178) and alpha Gly(181) strongly affects the equilibrium between active (closed) and inactive (open) conformations of the alpha-active site, the latter being stabilized in both mutants.

Allosteric Regulation↗

PubMed2002

Snapshots of the cystine lyase C-DES during catalysis. Studies in solution and in the crystalline state.

The cystine lyase (C-DES) of Synechocystis is a pyridoxal-5'-phosphate-dependent enzyme distantly related to the family of NifS-like proteins. The crystal structure of an N-terminal modified variant has recently been determined. Herein, the reactivity of this enzyme variant was investigated spectroscopically in solution and in the crystalline state to follow the course of the reaction and to determine the catalytic mechanism on a molecular level. Using the stopped-flow technique, the reaction with the preferred substrate cystine was found to follow biphasic kinetics leading to the formation of absorbing species at 338 and 470 nm, attributed to the external aldimine and the alpha-aminoacrylate; the reaction with cysteine also exhibited biphasic behavior but only the external aldimine accumulated. The same reaction intermediates were formed in crystals as seen by polarized absorption microspectrophotometry, thus indicating that C-DES is catalytically competent in the crystalline state. The three-dimensional structure of the catalytically inactive mutant C-DES(K223A) in the presence of cystine showed the formation of an external aldimine species, in which two alternate conformations of the substrate were observed. The combined results allow a catalytic mechanism to be proposed involving interactions between cystine and the active site residues Arg-360, Arg-369, and Trp-251*; these residues reorient during the beta-elimination reaction, leading to the formation of a hydrophobic pocket that stabilizes the enolimine tautomer of the aminoacrylate and the cysteine persulfide product.

Bacterial Proteins↗

PubMed2002

Simple, intuitive calculations of free energy of binding for protein-ligand complexes. 1. Models without explicit constrained water.

The prediction of the binding affinity between a protein and ligands is one of the most challenging issues for computational biochemistry and drug discovery. While the enthalpic contribution to binding is routinely available with molecular mechanics methods, the entropic contribution is more difficult to estimate. We describe and apply a relatively simple and intuitive calculation procedure for estimating the free energy of binding for 53 protein-ligand complexes formed by 17 proteins of known three-dimensional structure and characterized by different active site polarity. HINT, a software model based on experimental LogP(o/w) values for small organic molecules, was used to evaluate and score all atom-atom hydropathic interactions between the protein and the ligands. These total scores (H(TOTAL)), which have been previously shown to correlate with DeltaG(interaction) for protein-protein interactions, correlate with DeltaG(binding) for protein-ligand complexes in the present study with a standard error of +/-2.6 kcal mol(-1) from the equation DeltaG(binding) = -0.001 95 H(TOTAL) - 5.543. A more sophisticated model, utilizing categorized (by interaction class) HINT scores, produces a superior standard error of +/-1.8 kcal mol(-1). It is shown that within families of ligands for the same protein binding site, better models can be obtained with standard errors approaching +/-1.0 kcal mol(-1). Standardized methods for preparing crystallographic models for hydropathic analysis are also described. Particular attention is paid to the relationship between the ionization state of the ligands and the pH conditions under which the binding measurements are made. Sources and potential remedies of experimental and modeling errors affecting prediction of DeltaG(binding) are discussed.

Aldehyde-Lyases↗

PubMed2002

Crystals of tryptophan indole-lyase and tyrosine phenol-lyase form stable quinonoid complexes.

The binding of substrates and inhibitors to wild-type Proteus vulgaris tryptophan indole-lyase and to wild type and Y71F Citrobacter freundii tyrosine phenol-lyase was investigated in the crystalline state by polarized absorption microspectrophotometry. Oxindolyl-lalanine binds to tryptophan indole-lyase crystals to accumulate predominantly a stable quinonoid intermediate absorbing at 502 nm with a dissociation constant of 35 microm, approximately 10-fold higher than that in solution. l-Trp or l-Ser react with tryptophan indole-lyase crystals to give, as in solution, a mixture of external aldimine and quinonoid intermediates and gem-diamine and external aldimine intermediates, respectively. Different from previous solution studies (Phillips, R. S., Sundararju, B., & Faleev, N. G. (2000) J. Am. Chem. Soc. 122, 1008-1114), the reaction of benzimidazole and l-Trp or l-Ser with tryptophan indole-lyase crystals does not result in the formation of an alpha-aminoacrylate intermediate, suggesting that the crystal lattice might prevent a ligand-induced conformational change associated with this catalytic step. Wild-type tyrosine phenol-lyase crystals bind l-Met and l-Phe to form mixtures of external aldimine and quinonoid intermediates as in solution. A stable quinonoid intermediate with lambda(max) at 502 nm is accumulated in the reaction of crystals of Y71F tyrosine phenol-lyase, an inactive mutant, with 3-F-l-Tyr with a dissociation constant of 1 mm, approximately 10-fold higher than that in solution. The stability exhibited by the quinonoid intermediates formed both by wild-type tryptophan indole-lyase and by wild type and Y71F tyrosine phenol-lyase crystals demonstrates that they are suitable for structural determination by x-ray crystallography, thus allowing the elucidation of a key species of pyridoxal 5'-phosphate-dependent enzyme catalysis.

Catalysis↗