Kinds Of Subunits Research Articles

Family of Nanoclusters, Ln33 (Ln = Sm/Eu) and Gd32, Exhibiting Magnetocaloric Effects and Fluorescence Sensing for MnO4.

A family of nanoclusters, [Ln33(EDTA)12(OAc)2(CO3)4(μ3-OH)36(μ5-OH)4(H2O)38]·OAc·xH2O (x ≈ 50, Ln = Sm for 1; x ≈ 70, Ln = Eu for 2) and [Gd32(EDTA)12(OAc)2(C2O4)(CO3)2(μ3-OH)36(μ5-OH)4(H2O)36]·x(H2O) (x ≈ 70 for 3; H4EDTA = ethylene diamine tetraacetic acid), was prepared through the assembly of repeating subunits under the action of an anion template. The analysis of the structures showed that compounds 1 and 2 containing 33 Ln3+ ions were isostructural, which were constructed by three kinds of subunits in the presence of CO32- as an anion template, while compound 3 had a slightly different structure. Compound 3 containing 32 Gd3+ ions was formed by three types of subunits in the presence of CO32- and C2O42- as a mixed anion template. The CO32- anions came from the slow fixation of CO2 in the air. Meanwhile, one kind of high-nuclearity lanthanide clusters showed high chemical stability. The quantum Monte Carlo (QMC) calculation suggested that weak antiferromagnetic interactions were dominant between Gd3+ ions in 3. Magnetocaloric studies showed that compound 3 had a large entropy change of 43.0 J kg-1 K-1 at 2 K and 7 T. Surprisingly, compound 2 showed excellent recognition and detection effects for permanganate in aqueous solvents based on the fluorescence quenching phenomenon.

Effect of deep cryogenic treatment parameters on martensite multi-level microstructures and properties in a lath martensite/ferrite dual-phase steel

Abstract The microstructures and properties of a low-carbon 20CrNi2Mo–Al steel with martensite/ferrite dual-phase after deep cryogenic treatment (DCT) with different parameters were investigated. It was found that, with the increase of DCT processing time (QCT-h process) and cycle number (QCT-t process), the ferrite size was refined and its distribution became more homogeneous; the hardness and impact toughness were simultaneously increased. Especially in the QCT-t processes, the microstructure refinement and the property improvement were highly significant. The impact toughness of samples treated through 3-cycle DCT were 29.4% higher than the samples without DCT. Meanwhile, the martensite multi-level microstructures under different DCT parameters were thoroughly investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscattering diffraction (EBSD) and X-ray diffraction (XRD). Results showed that the size of martensite packet (dp), block (db) and lath (dl) decreased with increasing total DCT processing time. The Hall-Petch relationship was applied to discuss the relationship between the martensite multi-level microstructure and the impact toughness. According to the deflection degree of the crack propagation path at different crystallographic orientations, the effective control unit of the impact toughness was revealed to be block (db). The quantity of its boundaries increased most significantly among the three kinds of subunits, which had the strongest hindering effect on crack propagation.

Phosphofructokinase-1 subunit composition and activity in the skeletal muscle, liver, and brain of dogs.

Phosphofructokinase-1 (EC:2.7.1.11, PFK-1) catalyzes the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate using adenosine triphosphate and is a key regulatory enzyme of glycolysis. Mammalian PFK-1 isozymes are composed of three kinds of subunits (PFK-M, -L, and -P), with different properties. It has been suggested that the proportion of PFK-1 subunits in different organs is based on the organ energy metabolism. In this study, we analyzed the activity and subunit composition of canine PFK-1. We found that, in dogs, the skeletal muscle only has PFK-M, the liver mainly has PFK-L, and the brain expresses all of them. The knowledge of the composition of PFK-1 could provide useful information for determination of the differences in glycolysis in various organs of dogs.

Occurrence of a stonefish toxin-like toxin in the venom of the rabbitfish Siganus fuscescens

Rabbitfish belonging to the order Perciformes are well-known venomous fish that are frequently involved in human accidents. However little research has been done into either the whole venom toxicities or the structures and properties of their venom toxins. In this study, we first examined biological activities of the crude venom extract prepared from dorsal spines of Siganus fuscescens, a rabbitfish most commonly found along the coasts of Japan. As a result, the crude venom extract was shown to have mouse-lethal activity, hemolytic activity against rabbit erythrocytes, edema-forming activity and nociceptive activity, similar to the known scorpaeniform fish toxins (stonefish toxins and their analogues). Then, the primary structure of the S. fuscescens toxin was successfully elucidated by the same cDNA cloning strategy as previously employed for the toxins of some scorpaeniform fish (lionfish, devil stinger and waspfish). The S. fuscescens toxin is obviously an analogue of stonefish toxins, being composed of two kinds of subunits, an α-subunit of 703 amino acid residues and a β-subunit of 699 amino acid residues. Furthermore, the genes encoding both subunits were cloned from genomic DNA and shown to have an architecture of three exons and two introns, as reported for those of the scorpaeniform fish toxins. This study is the first to demonstrate the occurrence of stonefish toxin-like toxins in perciform fish.

Differential structure realization in humidity sensor

To realize the differential structure (which is an effective method to improve the sensitivity) in the humidity sensor, a novel differential humidity sensing structure, which has two kinds of sub units with opposite sensing properties, is designed. The content-based differential humidity sensing device made of conductive polymer composite is used as an example to exhibit the design method. The content-based differential humidity sensing device includes the “negative humidity coefficient unit (NHCU)” and the “positive humidity coefficient unit (PHCU)”. The sensitive material in NHCU/PHCU is the composite with low/high conductive phase content, which results in “a decrease”/“an increase” of the NHCU/PHCU resistance with the increase of the humidity. Through using NHCU and PHCU as the neighboring arms of an electrical bridge, the humidity is converted to a voltage. The results show that the “sensitivity”/“hysteresis error” can be increased/decreased by using the content-based differential structure. The “non-linear error”/“response time” of the content-based differential sensor is between those of NHCU and PHCU.

Structural constraints and dynamics of bacterial cell wall architecture.

The peptidoglycan wall (PG) is a unique structure which confers physical strength and defined shape to bacteria. It consists of a net-like macromolecule of peptide interlinked glycan chains overlying the cell membrane. The structure and layout of the PG dictates that the wall has to be continuously modified as bacteria go through division, morphological differentiation, and adaptive responses. The PG is poorly known in structural terms. However, to understand morphogenesis a precise knowledge of glycan strand arrangement and of local effects of the different kinds of subunits is essential. The scarcity of data led to a conception of the PG as a regular, highly ordered structure which strongly influenced growth models. Here, we review the structure of the PG to define a more realistic conceptual framework. We discuss the consequences of the plasticity of murein architecture in morphogenesis and try to define a set of minimal structural constraints that must be fulfilled by any model to be compatible with present day information.

Codon usage and coevolution of the large and small subunits of ribulose‐1,5‐bisphosphate carboxylase/oxygenase

AbstractAs the most abundant protein on Earth, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO) is the key enzyme in carbon fixation of photosynthesis in all green plants. It is hexadecimal polymer, consisting of two kinds of subunits, large and small ones, which are encoded by different genomes. The large subunit (LSU) is encoded by the chloroplast genome; the small one by the nuclear genome. The function of RuBisCO relies on the two subunits, and only when they are combined to be hexadecimal, can it carry out its whole function. However, how the LSU and small subunits evolved, and if they coevolved, has remained mysterious. In this study, based on data in 21 species, phylogenies were analyzed on two subunits, respectively, and a mirror tree was reconstructed to reveal phylogenetic similarity. Furthermore, a comparative analysis method, using the codon usage bias and correlation calculation for RuBisCO subunits, was carried out. The relative synonymous codon usage (RSCU) values of LSU and small subunits were calculated. Finally, a novel parameter, RSCU distances‐based correlation (RDC), for evaluating molecular coevolution was proposed based on Pearson's correlation coefficient between RSCU value matrices of two subunits. The results show that the topological similarity of the mirror tree gave positive evidence of coevolution between subunits. Similarly, the RDC was high, at 0.558, revealing that the RuBisCO subunits coevolved to an extent. The results confirmed that coevolution happened between the two subunits of RuBisCO, although they were encoded by different genomes. This study added new evidence that functional constraint plays an important role in the evolution of the two subunits.

Modulation of recombinant, α2*, α3* or α4*‐nicotinic acetylcholine receptor (nAChR) function by nAChR β3 subunits*

The nicotinic acetylcholine receptor (nAChR) β3 subunit is thought to serve an accessory role in nAChR subtypes expressed in dopaminergic regions implicated in drug dependence and reward. When β3 subunits are expressed in excess, they have a dominant-negative effect on function of selected nAChR subtypes. In this study, we show, in Xenopus oocytes expressing α2, α3 or α4 plus either β2 or β4 subunits, that in the presumed presence of similar amounts of each nAChR subunit, co-expression with wild-type β3 subunits generally (except for α3*-nAChR) lowers amplitudes of agonist-evoked, inward peak currents by 20-50% without having dramatic effects (≤ 2-fold) on agonist potencies. By contrast, co-expression with mutant β3(V9'S) subunits generally (except for α4β2*-nAChR) increases agonist potencies, consistent with an expected gain-of-function effect. This most dramatically demonstrates formation of complexes containing three kinds of subunit. Moreover, for oocytes expressing nAChR containing any α subunit plus β4 and β3(V9'S) subunits, there is spontaneous channel opening sensitive to blockade by the open channel blocker, atropine. Collectively, the results indicate that β3 subunits integrate into all of the studied receptor assemblies and suggest that natural co-expression with β3 subunits can influence levels of expression and agonist sensitivities of several nAChR subtypes.

Role of H-1 and H-2 Subunits of Soybean Seed Ferritin in Oxidative Deposition of Iron in Protein

Naturally occurring phytoferritin is a heteropolymer consisting of two different H-type subunits, H-1 and H-2. Prior to this study, however, the function of the two subunits in oxidative deposition of iron in ferritin was unknown. The data show that, upon aerobic addition of 48-200 Fe(2+)/shell to apoferritin, iron oxidation occurs only at the diiron ferroxidase center of recombinant H1 (rH-1). In addition to the diiron ferroxidase mechanism, such oxidation is catalyzed by the extension peptide (a specific domain found in phytoferritin) of rH-2, because the H-1 subunit is able to remove Fe(3+) from the center to the inner cavity better than the H-2 subunit. These findings support the idea that the H-1 and H-2 subunits play different roles in iron mineralization in protein. Interestingly, at medium iron loading (200 irons/shell), wild-type (WT) soybean seed ferritin (SSF) exhibits a stronger activity in catalyzing iron oxidation (1.10 ± 0.13 μm iron/subunit/s) than rH-1 (0.59 ± 0.07 μm iron/subunit/s) and rH-2 (0.48 ± 0.04 μm iron/subunit/s), demonstrating that a synergistic interaction exists between the H-1 and H-2 subunits in SSF during iron mineralization. Such synergistic interaction becomes considerably stronger at high iron loading (400 irons/shell) as indicated by the observation that the iron oxidation activity of WT SSF is ∼10 times larger than those of rH-1 and rH-2. This helps elucidate the widespread occurrence of heteropolymeric ferritins in plants.

Sequence analysis of dolphin ferritin H and L subunits and possible iron-dependent translational control of dolphin ferritin gene

BackgroundIron-storage protein, ferritin plays a central role in iron metabolism. Ferritin has dual function to store iron and segregate iron for protection of iron-catalyzed reactive oxygen species. Tissue ferritin is composed of two kinds of subunits (H: heavy chain or heart-type subunit; L: light chain or liver-type subunit). Ferritin gene expression is controlled at translational level in iron-dependent manner or at transcriptional level in iron-independent manner. However, sequencing analysis of marine mammalian ferritin subunits has not yet been performed fully. The purpose of this study is to reveal cDNA-derived amino acid sequences of cetacean ferritin H and L subunits, and demonstrate the possibility of expression of these subunits, especially H subunit, by iron.MethodsSequence analyses of cetacean ferritin H and L subunits were performed by direct sequencing of polymerase chain reaction (PCR) fragments from cDNAs generated via reverse transcription-PCR of leukocyte total RNA prepared from blood samples of six different dolphin species (Pseudorca crassidens, Lagenorhynchus obliquidens, Grampus griseus, Globicephala macrorhynchus, Tursiops truncatus, and Delphinapterus leucas). The putative iron-responsive element sequence in the 5'-untranslated region of the six different dolphin species was revealed by direct sequencing of PCR fragments obtained using leukocyte genomic DNA.ResultsDolphin H and L subunits consist of 182 and 174 amino acids, respectively, and amino acid sequence identities of ferritin subunits among these dolphins are highly conserved (H: 99–100%, (99→98) ; L: 98–100%). The conserved 28 bp IRE sequence was located -144 bp upstream from the initiation codon in the six different dolphin species.ConclusionThese results indicate that six different dolphin species have conserved ferritin sequences, and suggest that these genes are iron-dependently expressed.

SANS Observation of Abnormal Aggregation of Protein

Abnormal aggregation of lens protein, α-crystallin, has been observed with in situ small-angle neutron scattering under external stresses. Alpha-crystallin is a complex consisting of 40 subunits: there are two kinds of subunits, αA-crystallin and αB-crystallin. Single aggregate of αA-crystallin made structural deformation by temperature jump to the low temperature but did not by UV irradiation. On the other hand, that of αB-crystallin exhibited opposite response. These results suggested that α-crystallin could obtain tolerant against both external stresses by consisting of αA-crystallin and αB-crystallin. This assumption is also supported by another experimental result that the recombinant complex with αA-crystallin and αB-crystallin did not make the structural deformation by UV irradiation

Construction of an active acetohydroxyacid synthase I with a flexible linker connecting the catalytic and the regulatory subunits

Acetohydroxyacid synthase I (AHAS I), one of three isozymes in Escherichia coli catalyzing the first common step in the biosynthesis of branched amino acids, is composed of two kinds of subunits. The large catalytic (B) and small regulatory (N) subunits of the holoenzyme dissociate and associate freely and rapidly and are quite different in size, charge and hydrophobicity, so that high resolution purification methods lead to partial separation of subunits and to heterogeneity. We have prepared several linked AHAS I proteins, in which the large subunit B with a hexahistidine-tag at the N-terminus, was covalently joined by a flexible linker, containing several (X) amino acids, to the small subunit N to form His6-BuXN polypeptides. All linked BuXN polypeptides have similar specific activity, sensitivity to valine and substrate specificity as the wild type holoenzyme. The most successful BuXN linked protein (Bu30N-r) was inserted into and expressed in yeast and its catalytic properties were tested.

Structure and Mechanism of Vacuolar Na+-Translocating ATPase From Enterococcus hirae

V-type Na(+)-ATPase from Entercoccus hirae consists of nine kinds of subunits (NtpA(3), B(3), C(1), D(1), E(1-3), F(1-3), G(1), I(1), and K(10)) which are encoded by the ntp operon. The amino acid sequences of the major subunits, A, B, and K (proteolipid), were highly similar to those of A, B, and c subunits of eukaryotic V-ATPases, and those of beta, alpha, and c subunits of F-ATPases. We modeled the A and B subunits by homology modeling using the structure of beta and alpha subunits of F-ATPase, and obtained an atomic structure of NtpK ring by X-ray crystallography. Here we briefly summarize our current models of the whole structure and mechanism of the E. hirae V-ATPase.

Structure−Function Relationships of Soybean Proglycinins at Subunit Levels

Glycinin consists of five kinds of subunits, group I (A1aB1b, A1bB2, and A2B1a) and group II (A3B4 and A5A4B3). cDNAs for individual subunits were cloned by reverse transcription-polymerase chain reaction method and expressed in Escherichia coli using pET vector. The recombinant proglycinins were purified by ammonium sulfate fractionation and column chromatography in the form of homotrimers. Physicochemical properties such as molecular dimensions, solubility, surface hydrophobicity, thermal stability, and emulsifying ability of individual proglycinins were studied. Molecular dimensions were proportional to molecular size for all proglycinins except A2B1a. Solubility was intrinsic to each proglycinin. At the ionic strength of 0.5, all proglycinins except A1aB1b showed a very low solubility at acidic pH, but A1aB1b was soluble to higher than 60%. At ionic strength 0.08, all proglycinins exhibited isoelectric precipitation, although A2B1a and A1bB2 were not completely insoluble. The order of emulsifying ability (A1bB2 < A2B1a < A5A4B3 < A3B4 < or = A1aB1b) was not of the same for surface hydrophobicity (A5A4B3 < A1aB1b < or = A3B4 < A1bB2 < A2B1a) and thermal stability (A1bB2 << A2B1a < or = A5A4B3 < A3B4 < or = A1aB1b).

Positive and Negative Regulation of Nuclear Factor-κB-mediated Transcription by IκB-ζ, an Inducible Nuclear Protein

IkappaB-zeta is an inducible nuclear protein that interacts with nuclear factor-kappaB (NF-kappaB) via its carboxyl-terminal ankyrin-repeats. Previous studies using an NF-kappaB reporter have shown that IkappaB-zeta inhibits the activity of NF-kappaB. In the present study, we dissected the amino-terminal region of IkappaB-zeta, which shows no homology to any other proteins. Indirect immunofluorescence studies demonstrated the presence of a bipartite nuclear localization signal spanning amino acids 163-178. Using GAL4 fusion proteins, we found that internal fragments containing amino acids 329-402 possessed intrinsic transcriptional activation activity. Interestingly, the activity was not detected in GAL4 fusion proteins of the full-length IkappaB-zeta. On the other hand, the GAL4-dependent transcriptional activity was generated by co-expression of the GAL4-NF-kappaB p50 subunit fusion protein and the full-length IkappaB-zeta, neither of which exhibited the activity on their own. A new splicing variant, IkappaB-zeta(D), with a deletion of amino acids 236-429, was found to lack transactivation activity. Forced expression of IkappaB-zeta, but not IkappaB-zeta(D), augmented interleukin-6 production, indicating the functional significance of the transactivation activity. In contrast, tumor necrosis factor-alpha production was inhibited by expression of IkappaB-zeta, highlighting the dual functions of this molecule. These results indicate that IkappaB-zeta harbors latent transcriptional activation activity, and that the activity is expressed upon interaction with the NF-kappaB p50 subunit. In addition to the inhibitory activity on NF-kappaB-mediated transcription, the transcriptional activation activity of IkappaB-zeta should be crucial for the regulation of inflammation.

Structure−Physicochemical Function Relationships of Soybean Glycinin at Subunit Levels Assessed by Using Mutant Lines

Glycinin is a hexameric protein composed of five kinds of subunits. The subunits are classified into two groups, group I (A1aB1b, A1bB2, and A2B1a) and group II (A3B4 and A5A4B3). We purified four mutant glycinins composed of only group I subunits (group I-glycinin), only group II subunits (group II-glycinin), only A3B4 (A3B4-glycinin), and only A5A4B3 (A5A4B3-glycinin) from mutant soybean lines. The physicochemical properties of these glycinin samples were compared with those of the normal glycinin (11S) composed of five kinds of subunits. The thermal stabilities (as measured by thermal denaturation midpoint temperatures) of 11S, group I-glycinin, and group II-glycinin were similar to each other, although that of A3B4-glycinin was significantly lower than those of the others. The orders of aromatic and aliphatic surface hydrophobicities were the same: A3B4-glycinin > group II-glycinin > A5A4B3-glycinin > 11S > group I-glycinin. The solubility of 11S as a function of pH at mu = 0.5 was governed by that of group I-glycinin and followed this order at acidic pH: 11S = group I-glycinin > A3B4-glycinin > group II-glycinin = A5A4B3-glycinin. The order of emulsifying abilities was A5A4B3-glycinin > group II-glycinin > A3B4-glycinin > 11S > group I-glycinin. This order was consistent with that of the length of their hypervariable regions. Except for this relationship, there was no significant relationship among the other physicochemical properties of the mutant glycinins.

Crystal structure of soybean 11S globulin: glycinin A3B4 homohexamer.

Most plant seeds contain 11S globulins as major storage proteins for their nutrition. Soybean glycinin belongs to the 11S globulin family and consists of five kinds of subunits. We determined the crystal structure of a homohexamer of the glycinin A3B4 subunit at 2.1-A resolution. The crystal structure shows that the hexamer has 32-point group symmetry formed by face-to-face stacking of two trimers. The interface buries the highly conserved interchain disulfide. Based on the structure, we propose that an ingenious face-to-face mechanism controls the hexamer formation of the 11S globulin by movement of a mobile disordered region to the side of the trimer after posttranslational processing. Electrostatic analysis of the faces suggests that the interchain disulfide-containing face has high positive potential at acidic pH, which induces dissociation of the hexamer into trimers that may be susceptible to proteinases after seed imbibition. This dissociation might result in the degradation and mobilization of 11S globulins as storage proteins in embryos during germination and seedling growth.

Regulation by cycloheximide and lowered temperature of cell-surface alpha7-nicotinic acetylcholine receptor expression on transfected SH-EP1 cells.

Heterologous expression of functional, nicotinic acetylcholine receptors (nAChR) in mammalian cells has been difficult to achieve or optimize, even for nAChR containing only one kind of subunit. In this study, we determined effects of lowered temperature or of exposure to the protein synthesis inhibitor cycloheximide (CHX) on cell surface expression of homomeric alpha7-nAChR in transfected SH-EP1 human epithelial cells. We found that incubation of cells for 2 days at 25 degrees C or in the presence of 0.5-2 microg/mL of CHX caused approximately four- or approximately eight-fold increases, respectively, in surface binding sites for 125I-labeled alpha-bungarotoxin (I-Bgt). These increases were accompanied by increases in peak whole-cell current responses to nicotinic agonists. Either treatment lowered protein synthesis and cell proliferation, but experiments using puromycin indicated that a reduction in protein synthesis or cell proliferation per se was not sufficient to increase surface binding. I-Bgt binding to whole-cell membrane pools increased in response to either treatment, suggesting that the increase in surface binding was due, at least in part, to an increase in intracellular receptor levels. The cyclophilin inhibitor cyclosporin A reduced surface expression in untreated as well as CHX- or 25 degrees C-treated cells. The results suggest practical means for increasing cell surface and functional expression of alpha7-nAChR. Although these effects are not simply due to protein synthesis inhibition or reduced cell proliferation, they do involve an increase in intracellular receptor pool size.

Creation of soybean β-conglycinin β with strong phagocytosis-stimulating activity

β-Conglycinin is composed of three kinds of subunit: α, α′ and β. A phagocytosis-stimulating peptide sequence (MITLAIPVNKPGR), soymetide, exists in the α′ subunit of β-conglycinin. Met at N terminus of the soymetide is essential for the activity. When Thr at the third residue from N terminus of the soymetide is replaced by Phe or Trp, the phagocytosis-stimulating activity greatly increases (Thr<Phe<Trp). The β subunit does not exhibit the phagocytosis-stimulating activity because the residues corresponding to the first and third residues in the soymetide are Ile and Lys, respectively. In this study, we introduced the phagocytosis-stimulating peptide sequence (Ile→Met, Lys→Thr, Phe, or Trp) into the β subunit after confirmation of the effects of residue replacements by molecular modeling, suggesting that the introduced mutations might not prevent the correct folding. The studies of circular dichroism (CD), gel filtration and differential scanning calorimetry (DSC) of the mutants (I122M/K124T, I122M/K124F, I122M/K124W) expressed in E. coli demonstrated that they folded and self-assembled similarly to the wild type. This was confirmed by X-ray analysis of I122M/K124W crystal where the biggest residue tryptophane was introduced. The three mutants exhibited phagocytosis activities after digestion by trypsin, and the order was the wild type<I122M/K124T<I122M/K124F<I122M/K124W as expected.

Crystallization and preliminary X-ray characterization of archaeal group II chaperonin alpha-subunit from Thermococcus strain KS-1.

The archaeal group II chaperonin from Thermococcus strain KS-1 is composed of two kinds of subunits (alpha and beta). Each of the recombinant subunits was individually expressed in Escherichia coli and purified as homo-hexadecamers of each subunit. Both homo-oligomers facilitate the refolding of denatured proteins in vitro in an ATP-dependent manner. A mutant alpha-subunit homo-oligomer with two amino-acid substitutions, which has the ability to capture the unfolded protein but lacks the ability to refold the unfolded protein, was crystallized in two different conditions. One crystal form was obtained from a high-concentration solution of ammonium sulfate and grew to maximum dimensions of 0.15 x 0.15 x 0.4 mm. The crystals of this form belonged to the tetragonal space group P42(1)2, with unit-cell parameters a = b = 209.3, c = 156.1 A, and diffracted X-rays to 2.4 A resolution with synchrotron radiation. The other form was crystallized from a polyethylene glycol 6000 solution and belonged to the tetragonal space group, with unit-cell parameters a = b = 220.8, c = 182.4 A. This form only diffracts X-rays to 6 A resolution. Diffraction data collected from the former crystal enabled initial successful phases to be obtained by the molecular-replacement method.