A randomized trial to investigate needle redirections/re-insertions using a handheld ultrasound device versus traditional palpation for spinal anesthesia in obese women undergoing cesarean delivery

BACKGROUND

Ultrasound may be useful to identify the spinal anesthesia insertion point, particularly when landmarks are not palpable. We tested the hypothesis that the number of needle redirections/re-insertions is lower when using a handheld ultrasound device compared with palpation in obese women undergoing spinal anesthesia for cesarean delivery.

METHODS

Study recruits were obese (body mass index (BMI) >30 kg/m²) women with impalpable bony landmarks who were undergoing spinal anesthesia for elective cesarean delivery. Women were randomized to ultrasound or palpation. The primary study outcome was a composite between-group comparison of total number of needle redirections (any withdrawal and re-advancement of the needle and/or introducer within the intervertebral space) or re-insertions (any new skin puncture in the same or different intervertebral space) per patient. Secondary outcomes included insertion site identification time and patient verbal numerical pain score (0-10) for comfort during surgical skin incision.

RESULTS

Forty women completed the study. The mean BMI (standard deviation) for the ultrasound group was 39.8 (5.5) kg/m² and for the palpation group 37.3 (5.2) kg/m². There was no difference in the composite primary outcome (median (interquartile range) [range]) between the ultrasound group (4 (2-13) [2-22]) and the (6 (4-10) [1-17]) palpation group (P=0.22), with the 95% confidence interval of the difference 2 (-1.7 to 5.7). There were no differences in the secondary outcomes.

CONCLUSIONS

Handheld ultrasound did not demonstrate any advantages over traditional palpation techniques for spinal anesthesia in an obese population undergoing cesarean delivery, although the study was underpowered to show a difference.

The environment and antiphospholipid syndrome

The etiology of autoimmune diseases is multifactorial. The degree to which genetic and environmental factors influence susceptibility to autoimmune diseases is poorly defined. It is believed that versatile clinical presentations of autoimmune diseases stem from various combinations of the genetic and environmental factors. One of the newly diagnosed autoimmune diseases is the antiphospholipid syndrome (APS). APS is characterized by vascular thrombosis, and/or pregnancy morbidity associated with anticardiolipin (aCL), anti-β2-glycoprotein-I (anti-β2GPI) and lupus anticoagulant (LAC).

A structural view of the dissociation of Escherichia coli tryptophanase

Tryptophanase (Trpase) is a pyridoxal 5'-phosphate (PLP)-dependent homotetrameric enzyme which catalyzes the degradation of L-tryptophan. Trpase is also known for its cold lability, which is a reversible loss of activity at low temperature (2°C) that is associated with the dissociation of the tetramer. Escherichia coli Trpase dissociates into dimers, while Proteus vulgaris Trpase dissociates into monomers. As such, this enzyme is an appropriate model to study the protein-protein interactions and quaternary structure of proteins. The aim of the present study was to understand the differences in the mode of dissociation between the E. coli and P. vulgaris Trpases. In particular, the effect of mutations along the molecular axes of homotetrameric Trpase on its dissociation was studied. To answer this question, two groups of mutants of the E. coli enzyme were created to resemble the amino-acid sequence of P. vulgaris Trpase. In one group, residues 15 and 59 that are located along the molecular axis R (also termed the noncatalytic axis) were mutated. The second group included a mutation at position 298, located along the molecular axis Q (also termed the catalytic axis). Replacing amino-acid residues along the R axis resulted in dissociation of the tetramers into monomers, similar to the P. vulgaris Trpase, while replacing amino-acid residues along the Q axis resulted in dissociation into dimers only. The crystal structure of the V59M mutant of E. coli Trpase was also determined in its apo form and was found to be similar to that of the wild type. This study suggests that in E. coli Trpase hydrophobic interactions along the R axis hold the two monomers together more strongly, preventing the dissociation of the dimers into monomers. Mutation of position 298 along the Q axis to a charged residue resulted in tetramers that are less susceptible to dissociation. Thus, the results indicate that dissociation of E. coli Trpase into dimers occurs along the molecular Q axis.

Structures of Escherichia coli tryptophanase in holo and 'semi-holo' forms

Two crystal forms of Escherichia coli tryptophanase (tryptophan indole-lyase, Trpase) were obtained under the same crystallization conditions. Both forms belonged to the same space group P43212 but had slightly different unit-cell parameters. The holo crystal form, with pyridoxal phosphate (PLP) bound to Lys270 of both polypeptide chains in the asymmetric unit, diffracted to 2.9 Å resolution. The second crystal form diffracted to 3.2 Å resolution. Of the two subunits in the asymmetric unit, one was found in the holo form, while the other appeared to be in the apo form in a wide-open conformation with two sulfate ions bound in the vicinity of the active site. The conformation of all holo subunits is the same in both crystal forms. The structures suggest that Trpase is flexible in the apo form. Its conformation partially closes upon binding of PLP. The closed conformation might correspond to the enzyme in its active state with both cofactor and substrate bound in a similar way as in tyrosine phenol-lyase.

Inhibition of inositol monophosphatase (IMPase) at the calbindin-D28k binding site: molecular and behavioral aspects

Bipolar-disorder (manic-depressive illness) is a severe chronic illness affecting ∼1% of the adult population. It is treated with mood-stabilizers, the prototypic one being lithium-salts (lithium), but it has life threatening side-effects and a significant number of patients fail to respond. The lithium-inhibitable enzyme inositol-monophosphatase (IMPase) is one of the viable targets for lithium's mechanism of action. Calbindin-D28k (calbindin) up-regulates IMPase activity. The IMPase-calbindincomplex was modeled using the program MolFit. The in-silico model indicated that the 55-66 amino-acid segment of IMPase anchors calbindin via Lys59 and Lys61 with a glutamate in between (Lys-Glu-Lys motif) and that the motif interacts with residues Asp24 and Asp26 of calbindin. We found that differently from wildtype calbindin, IMPase was not activated by mutated calbindin in which Asp24 and Asp26 were replaced by alanine. Calbindin's effect was significantly reduced by a linear peptide with the sequence of amino acids 58-63 of IMPase (peptide 1) and by six amino-acid linear peptides including at least part of the Lys-Glu-Lys motif. The three amino-acid peptide Lys-Glu-Lys or five amino-acid linear peptides containing this motif were ineffective. Mice administered peptide 1 intracerebroventricularly exhibited a significant anti-depressant-like reduced immobility in the forced-swim test. Based on the sequence of peptide 1, and to potentially increase the peptide's stability, cyclic and linear pre-cyclic analog peptides were synthesized. One cyclic peptide and one linear pre-cyclic analog peptide inhibited calbindin-activated brain IMPase activity in-vitro. Our findings may lead to the development of molecules capable of inhibiting IMPase activity at an alternative site than that of lithium.

Increased adipocyte S-nitrosylation targets anti-lipolytic action of insulin: relevance to adipose tissue dysfunction in obesity

Protein S-nitrosylation is a reversible protein modification implicated in both physiological and pathophysiological regulation of protein function. In obesity, skeletal muscle insulin resistance is associated with increased S-nitrosylation of insulin-signaling proteins. However, whether adipose tissue is similarly affected in obesity and, if so, what are the causes and functional consequences of increased S-nitrosylation in this tissue are unknown. Total protein S-nitrosylation was increased in intra-abdominal adipose tissue of obese humans and in high fat-fed or leptin-deficient ob/ob mice. Both the insulin receptor β-subunit and Akt were S-nitrosylated, correlating with body weight. Elevated protein and mRNA expression of inducible NO synthase and decreased protein levels of thioredoxin reductase were associated with increased adipose tissue S-nitrosylation. Cultured differentiated pre-adipocyte cell lines exposed to the NO donors S-nitrosoglutathione (GSNO) or S-nitroso-N-acetylpenicillamine exhibited diminished insulin-stimulated phosphorylation of Akt but not of GSK3 nor of insulin-stimulated glucose uptake. Yet the anti-lipolytic action of insulin was markedly impaired in both cultured adipocytes and in mice injected with GSNO prior to administration of insulin. In cells, impaired ability of insulin to diminish phosphorylated PKA substrates in response to isoproterenol suggested impaired insulin-induced activation of PDE3B. Consistently, increased S-nitrosylation of PDE3B was detected in adipose tissue of high fat-fed obese mice. Site-directed mutagenesis revealed that Cys-768 and Cys-1040, two putative sites for S-nitrosylation adjacent to the substrate-binding site of PDE3B, accounted for ∼50% of its GSNO-induced S-nitrosylation. Collectively, PDE3B and the anti-lipolytic action of insulin may constitute novel targets for increased S-nitrosylation of adipose tissue in obesity.

Inhibition of specific adenylyl cyclase isoforms by lithium and carbamazepine, but not valproate, may be related to their antidepressant effect

OBJECTIVES

Lithium, valproate, and carbamazepine decrease stimulated brain cyclic-AMP (cAMP) levels. Adenylyl cyclase (AC), of which there are nine membrane-bound isoforms (AC1-AC9), catalyzes the formation of cAMP. We have recently demonstrated preferential inhibition of AC5 by lithium. We now sought to determine whether carbamazepine and valproate also preferentially inhibit specific AC isoforms or decrease cAMP levels via different mechanisms.

METHODS

COS7 cells were transfected with one of AC1-AC9, with or without D1-dopamine receptors. Carbamazepine's and valproate's effect on forskolin- or D1 agonist-stimulated ACs was studied. The effect of Mg(2+) on lithium's inhibition was studied in membrane-enriched fraction from COS7 cells co-expressing AC5 and D1 receptors. AC5 knockout mice were tested for a behavioral phenotype similar to that of lithium treatment.

RESULTS

Carbamazepine preferentially inhibited forskolin-stimulated AC5 and AC1 and all D1 agonist-stimulated ACs, with AC5 and AC7 being the most sensitive. When compared to 1 or 3 mM Mg(2+), 10 mM Mg(2+) reduced lithium-induced AC5 inhibition by 70%. In silico modeling suggests that among AC isoforms carbamazepine preferentially affects AC1 and AC5 by interacting with the catechol-estrogen site. Valproate did not affect any forskolin- or D1 receptor-stimulated AC. AC5 knockout mice responded similarly to antidepressant- or lithium-treated wild-types in the forced-swim test but not in the amphetamine-induced hyperactivity mania model.

CONCLUSIONS

Lithium and carbamazepine preferentially inhibit AC5, albeit via different mechanisms. Lithium competes with Mg(2+), which is essential for AC activity; carbamazepine competes for AC's catechol-estrogen site. Antidepressant-like behavior of AC5 knockout mice in the forced-swim test supports the notion that AC5 inhibition is involved in the antidepressant effect of lithium and carbamazepine. The effect of lithium and carbamazepine to lower cAMP formation in AC5-rich dopaminergic brain regions suggests that D1-dopamine receptors in these regions are involved in the antidepressant effect of mood stabilizers.

The crystal structures of the psychrophilic subtilisin S41 and the mesophilic subtilisin Sph reveal the same calcium-loaded state

We determine and compare the crystal structure of two proteases belonging to the subtilisin superfamily: S41, a cold-adapted serine protease produced by Antarctic bacilli, at 1.4 A resolution and Sph, a mesophilic serine protease produced by Bacillus sphaericus, at 0.8 A resolution. The purpose of this comparison was to find out whether multiple calcium ion binding is a molecular factor responsible for the adaptation of S41 to extreme low temperatures. We find that these two subtilisins have the same subtilisin fold with a root mean square between the two structures of 0.54 A. The final models for S41 and Sph include a calcium-loaded state of five ions bound to each of these two subtilisin molecules. None of these calcium-binding sites correlate with the high affinity known binding site (site A) found for other subtilisins. Structural analysis of the five calcium-binding sites found in these two crystal structures indicate that three of the binding sites have two side chains of an acidic residue coordinating the calcium ion, whereas the other two binding sites have either a main-chain carbonyl, or only one acidic residue side chain coordinating the calcium ion. Thus, we conclude that three of the sites are of high affinity toward calcium ions, whereas the other two are of low affinity. Because Sph is a mesophilic subtilisin and S41 is a psychrophilic subtilisin, but both crystal structures were found to bind five calcium ions, we suggest that multiple calcium ion binding is not responsible for the adaptation of S41 to low temperatures.

Structural insights into cold inactivation of tryptophanase and cold adaptation of subtilisin S41

A wide variety of enzymes can undergo a reversible loss of activity at low temperature, a process that is termed cold inactivation. This phenomenon is found in oligomeric enzymes such as tryptophanase (Trpase) and other pyridoxal phosphate dependent enzymes. On the other hand, cold-adapted, or psychrophilic enzymes, isolated from organisms able to thrive in permanently cold environments, have optimal activity at low temperature, which is associated with low thermal stability. Since cold inactivation may be considered "contradictory" to cold adaptation, we have looked into the amino acid sequences and the crystal structures of two families of enzymes, subtilisin and tryptophanase. Two cold adapted subtilisins, S41 and subtilisin-like protease from Vibrio, were compared to a mesophilic and a thermophilic subtilisins, as well as to four PLP-dependent enzymes in order to understand the specific surface residues, specific interactions, or any other molecular features that may be responsible for the differences in their tolerance to cold temperatures. The comparison between the psychrophilic and the mesophilic subtilisins revealed that the cold adapted subtilisins have a high content of acidic residues mainly found on their surface, making it charged. The analysis of the Trpases showed that they have a high content of hydrophobic residues on their surface. Thus, we suggest that the negatively charged residues on the surface of the subtilisins may be responsible for their cold adaptation, whereas the hydrophobic residues on the surface of monomeric Trpase molecules are responsible for the tetrameric assembly, and may account for their cold inactivation and dissociation.

SP1 protein-based nanostructures and arrays

Controlled formation of complex nanostructures is one of the main goals of nanoscience and nanotechnology. Stable Protein 1 (SP1) is a boiling-stable ring protein complex, 11 nm in diameter, which self-assembles from 12 identical monomers. SP1 can be utilized to form large ordered arrays; it can be easily modified by genetic engineering to produce various mutants; it is also capable of binding gold nanoparticles (GNPs) and thus forming protein-GNP chains made of alternating SP1s and GNPs. We report the formation and the protocols leading to the formation of those nanostructures and their characterization by transmission electron microscopy, atomic force microscopy, and electrostatic force microscopy. Further control over the GNP interdistances within the protein-GNP chains may lead to the formation of nanowires and structures that may be useful for nanoelectronics.

The structure of apo tryptophanase fromEscherichia colireveals a wide-open conformation

The crystal structure of apo tryptophanase from Escherichia coli (space group F222, unit-cell parameters a = 118.4, b = 120.1, c = 171.2 A) was determined at 1.9 A resolution using the molecular-replacement method and refined to an R factor of 20.3% (R(free) = 23.2%). The structure revealed a significant shift in the relative orientation of the domains compared with both the holo form of Proteus vulgaris tryptophanase and with another crystal structure of apo E. coli tryptophanase, reflecting the internal flexibility of the molecule. Domain shifts were previously observed in tryptophanase and in the closely related enzyme tyrosine phenol-lyase, with the holo form found in an open conformation and the apo form in either an open or a closed conformation. Here, a wide-open conformation of the apo form of tryptophanase is reported. A conformational change is also observed in loop 297-303. The structure contains a hydrated Mg(2+) at the cation-binding site and a Cl(-) ion at the subunit interface. The enzyme activity depends on the nature of the bound cation, with smaller ions serving as inhibitors. It is hypothesized that this effect arises from variations of the coordination geometry of the bound cation.

Binding assay and preliminary X-ray crystallographic analysis of ACTIBIND, a protein with anticarcinogenic and antiangiogenic activities

ACTIBIND is a T2 RNase extracellular glycoprotein produced by the mould Aspergillus niger B1 (CMI CC 324626) that possesses anticarcinogenic and antiangiogenic activities. ACTIBIND was found to be an actin-binding protein that interacts with rabbit muscle actin in a 1:2 molar ratio (ACTIBIND:actin) with a binding constant of 16.17 x 10(4) M(-1). Autoclave-treated ACTIBIND (EI-ACTIBIND) lost its RNase activity, but its actin-binding ability was conserved. ACTIBIND crystals were grown using 20% PEG 3350, 0.2 M ammonium dihydrogen phosphate solution at room temperature (293 K). One to four single crystals appeared in each droplet within a few days and grew to approximate dimensions of 0.5 x 0.5 x 0.5 mm after about two weeks. Diffraction studies of these crystals at low temperature (100 K) indicated that they belong to the P3(1)21 space group, with unit-cell parameters a = 78, b = 78, c = 104 A.

Drosophila Dynein light chain (DDLC1) binds to gurken mRNA and is required for its localization

During oogenesis in Drosophila, mRNAs encoding determinants required for the polarization of egg and embryo become localized in the oocyte in a spatially restricted manner. The TGF-alpha like signaling molecule Gurken has a central role in the polarization of both body axes and the corresponding mRNA displays a unique localization pattern, accumulating initially at the posterior and later at the anterior-dorsal of the oocyte. Correct localization of gurken RNA requires a number of cis-acting sequence elements, a complex of trans-acting proteins, of which only several have been identified, and the motor proteins Dynein and Kinesin, traveling along polarized microtubules. Here we report that the cytoplasmic Dynein-light-chain (DDLC1) which is the cargo-binding subunit of the Dynein motor protein, directly bound with high specificity and affinity to a 230-nucleotide region within the 3'UTR of gurken, making it the first Drosophila mRNA-cargo to directly bind to the DLC. Although DDLC1 lacks known RNA-binding motifs, comparison to double-stranded RNA-binding proteins suggested structural resemblance. Phenotypic analysis of ddlc1 mutants supports a role for DDLC1 in gurken RNA localization and anchoring as well as in correct positioning of the oocyte nucleus.

The structural basis of the thermostability of SP1, a novel plant (Populus tremula) boiling stable protein

We previously reported on a new boiling stable protein isolated from aspen plants (Populus tremula), which we named SP1. SP1 is a stress-related protein with no significant sequence homology to other stress-related proteins. It is a 108-amino-acid hydrophilic polypeptide with a molecular mass of 12.4 kDa (Wang, W. X., Pelah, D., Alergand, T., Shoseyov, O., and Altman, A. (2002) Plant Physiol. 130, 865-875) and is found in an oligomeric form. Preliminary electron microscopy studies and matrix-assisted laser desorption ionization time-of-flight mass spectrometry experiments showed that SP1 is a dodecamer composed of two stacking hexamers. We performed a SDS-PAGE analysis, a differential scanning calorimetric study, and crystal structure determination to further characterize SP1. SDS-PAGE indicated a spontaneous assembly of SP1 to one stable oligomeric form, a dodecamer. Differential scanning calorimetric showed that SP1 has high thermostability i.e. Tm of 107 degrees C (at pH 7.8). The crystal structure of SP1 was initially determined to 2.4 A resolution by multi-wavelength anomalous dispersion method from a crystal belonging to the space group I422. The phases were extended to 1.8 A resolution using data from a different crystal form (P21). The final refined molecule includes 106 of the 108 residues and 132 water molecules (on average for each chain). The R-free is 20.1%. The crystal structure indicated that the SP1 molecule has a ferredoxin-like fold. Strong interactions between each two molecules create a stable dimer. Six dimers associate to form a ring-like-shaped dodecamer strongly resembling the particle visualized in the electron microscopy studies. No structural similarity was found between the crystal structure of SP1 and the crystal structure of other stress-related proteins such as small heat shock proteins, whose structure has been already determined. This structural study further supports our previous report that SP1 may represent a new family of stress-related proteins with high thermostability and oligomerization.

The 0.93Å Crystal Structure of Sphericase: A Calcium-loaded Serine Protease from Bacillus sphaericus

We have previously isolated sphericase (Sph), an extracellular mesophilic serine protease produced by Bacillus sphaericus. The Sph amino acid sequence is highly homologous to two cold-adapted subtilisins from Antarctic bacilli S39 and S41 (76% and 74% identity, respectively). Sph is calcium-dependent, 310 amino acid residues long and has optimal activity at pH 10.0. S41 and S39 have not as yet been structurally analysed. In the present work, we determined the crystal structure of Sph by the Eu/multiwavelength anomalous diffraction method. The structure was extended to 0.93A resolution and refined to a crystallographic R-factor of 9.7%. The final model included all 310 amino acid residues, one disulfide bond, 679 water molecules and five calcium ions. Although Sph is a mesophilic subtilisin, its amino acid sequence is similar to that of the psychrophilic subtilisins, which suggests that the crystal structure of these subtilisins is very similar. The presence of five calcium ions bound to a subtilisin molecule, as found here for Sph, has not been reported for the subtilisin superfamily. None of these calcium-binding sites correlates with the well-known high-affinity calcium-binding site (site I or site A), and only one site has been described previously. This calcium-binding pattern suggests that a reduction in the flexibility of the surface loops of Sph by calcium binding may be responsible for its adaptation to mesophilic organisms.

Crystallization and preliminary X-ray crystallographic analysis of SP1, a novel chaperone-like protein

SP1 (108 amino acids) is a boiling-stable stress-responsive protein. It has no significant sequence homology to other stress-related proteins or to small heat-shock proteins (sHsps). SP1 activity is ATP-independent, similar to other small heat-shock proteins. Based on these features, it is expected that the structure-function relationship of SP1 will be unique. In this work, the crystallization and preliminary crystallographic data of native SP1 and its selenomethionine derivative are described. Recombinant SP1 and its selenomethionine derivative were expressed in Escherichia coli and used for crystallization experiments. SP1 crystals were grown from 0.1 M HEPES pH 7.5, 20% PEG 3K, 0.2 M NaCl. One to four single crystals appeared in each droplet within a few Days and grew to dimensions of about 0.5 x 0.5 x 0.8 mm after about two weeks. Diffraction studies of these crystals at low temperature indicated that they belong to space group I422, with unit-cell parameters a = 89, b = 89, c = 187 A. Efforts to crystallize the selenomethionine derivative of SP1 are in progress.

Structural basis of thermostability. Analysis of stabilizing mutations in subtilisin BPN'

The crystal structures of two thermally stabilized subtilisin BPN' variants, S63 and S88, are reported here at 1.8 and 1.9 A resolution, respectively. The micromolar affinity calcium binding site (site A) has been deleted (Delta75-83) in these variants, enabling the activity and thermostability measurements in chelating conditions. Each of the variants includes mutations known previously to increase the thermostability of calcium-independent subtilisin in addition to new stabilizing mutations. S63 has eight amino acid replacements: D41A, M50F, A73L, Q206W, Y217K, N218S, S221C, and Q271E. S63 has 75-fold greater stability than wild type subtilisin in chelating conditions (10 mm EDTA). The other variant, S88, has ten site-specific changes: Q2K, S3C, P5S, K43N, M50F, A73L, Q206C, Y217K, N218S, and Q271E. The two new cysteines form a disulfide bond, and S88 has 1000 times greater stability than wild type subtilisin in chelating conditions. Comparisons of the two new crystal structures (S63 in space group P2(1) with A cell constants 41.2, 78.1, 36.7, and beta = 114.6 degrees and S88 in space group P2(1)2(1)2(1) with cell constants 54.2, 60.4, and 82.7) with previous structures of subtilisin BPN' reveal that the principal changes are in the N-terminal region. The structural bases of the stabilization effects of the new mutations Q2K, S3C, P5S, D41A, Q206C, and Q206W are generally apparent. The effects are attributed to the new disulfide cross-link and to improved hydrophobic packing, new hydrogen bonds, and other rearrangements in the N-terminal region.

Mutations at vicinity of catalytic sites of hepatitis C virus NS3 serine protease gene isolated from hepatocellular carcinoma tissue

The mechanism of hepatitis C virus (HCV) -induced hepatotocellular carcinoma (HCC) is still unknown, but in vitro studies clearly suggest that HCV proteins exert a direct effect on liver carcinogenesis. HCV NS3 serine protease is known to play a key role in the life cycle of the virus and may interact with the host cellular regulatory proteins. The aim of the present study was to conduct a genetic analysis of the HCV NS3 gene coding for the serine protease isolated from serum, tumor, and nontumor tissue of HCC patients. RNA was extracted and HCV cDNA was amplified by nested reverse transcriptase-polymerase chain reaction (RT-PCR). Sequence comparison yielded unique changes at the vicinity of the catalytic sites of the NS3 clones isolated only from HCC tissue. These changes included the insertion of a "large" and charged amino acid, substitution of a polar with a hydrophobic amino acid, and substitution of a charged with a polar amino acid. Those changes affect the electrostatic charge around the active site, and thus the activity and substrate specificity of the serine protease. This is the first study to define significant amino acid changes at the catalytic domain of the NS3 serine protease gene isolated from HCC tissue.

Primary and tertiary structures of the Fab fragment of a monoclonal anti-E-selectin 7A9 antibody that inhibits neutrophil attachment to endothelial cells

The murine monoclonal IgG1 antibody 7A9 binds specifically to the endothelial leukocyte adhesion molecule-1 (E-selectin), inhibiting the attachment of neutrophils to endothelial cells. The primary and three-dimensional structures of the Fab fragment of 7A9 are reported. The amino acid sequence was determined by automated Edman degradation analysis of proteolytic fragments of both the heavy and light chains of the Fab. The sequences of the two chains are consistent with that of the IgG1 class with an associated kappa light chain with two intrachain disulfide bridges in each of the heavy and light chains. The tertiary structure of the antibody fragment was determined by x-ray crystallographic methods at 2.8 A resolution. The F(ab')2 molecule, treated with dithiothreitol, crystallizes in the space group P2(1) 2(1) 2(1) with unit cell parameters a = 44.5 A, b = 83.8 A, and c = 132.5 A with one Fab molecule in the asymmetric unit. The structure was solved by the molecular replacement method and subsequently refined using simulated annealing followed by conventional least squares optimization of the coordinates. The resulting model has reasonable stereochemistry with an R factor of 0.195. The 7A9 Fab structure has an elbow bend of 162 degrees and is remarkably similar to that of the monoclonal anti-intercellular adhesion molecule-1 (ICAM-1) antibody Fab fragment. The 7A9 antigen combining site presents a groove resembling the structure of the anti-ICAM-1 antibody, and other antibodies raised against surface receptors and peptides. Residues from the six complementary determining regions (CDRs) and framework residues form the floor and walls of the groove that is approximately 22 A wide and 8 A deep and that is lined with many aromatic residues. The groove is large enough to accommodate the loop between beta-strands beta4 and beta5 of the lectin domain of E-selectin that has been implicated in neutrophil adhesion (1).

Crystal structure of the disulfide-stabilized Fv fragment of anticancer antibody B1: conformational influence of an engineered disulfide bond

A recombinant Fv construct of the B1 monoclonal antibody that recognizes the LewisY-related carbohydrate epitope on human carcinoma cells has been prepared. The Fv is composed of the polypeptide chains of the VH and VL domains expressed independently and isolated as inclusion bodies. The Fv is prepared by combining and refolding equimolar amounts of guanidine chloride solubilized inclusion bodies. The Fv is stabilized by an engineered interchain disulfide bridge between residues VL100 and VH44. This construct has a similar binding affinity as that of the single-chain construct (Benhar and Pastan, Clin. Cancer Res. 1:1023-1029, 1995). The B1 disulfide-stabilized Fv (BldsFv) crystallizes in space group P6(1)22 with the unit cell parameters a = b = 80.1 A, and c = 138.1 A. The crystal structure of the BldsFv has been determined at 2.1-A resolution using the molecular replacement technique. The final structure has a crystallographic R-value of 0.187 with a root mean square deviation in bond distance of 0.014 A and in bond angle of 2.74 degrees. Comparisons of the BldsFv structure with known structures of Fv regions of other immunoglobulin fragments shows closely related secondary and tertiary structures. The antigen combining site of BldsFv is a deep depression 10-A wide and 17-A long with the walls of the depression composed of residues, many of which are tyrosines, from complementarity determining regions L1, L3, H1, H2, and H3. Model building studies indicate that the LewisY tetrasaccharide, Fuc-Gal-Nag-Fuc, can be accommodated in the antigen combining site in a manner consistent with the epitope predicted in earlier biochemical studies (Pastan, Lovelace, Gallo, Rutherford, Magnani, and Willingham, Cancer Res. 51:3781-3787, 1991). Thus, the engineered disulfide bridge appears to cause little, if any, distortion in the Fv structure, making it an effective substitute for the B1 Fab.

Crystal structure of calcium-independent subtilisin BPN' with restored thermal stability folded without the prodomain

The three-dimensional structure of a subtilisin BPN' construct that was produced and folded without its prodomain shows the tertiary structure is nearly identical to the wild-type enzyme and not a folding intermediate. The subtilisin BPN' variant, Sbt70, was cloned and expressed in Escherichia coli without the prodomain, the 77-residue N-terminal domain that catalyzes the folding of the enzyme into its native tertiary structure. Sbt70 has the high-affinity calcium-binding loop, residues 75 to 83, deleted. Such calcium-independent forms of subtilisin BPN' refold independently while retaining high levels of activity [Bryan et al., Biochemistry, 31:4937-4945, 1992]. Sbt70 has, in addition, seven stabilizing mutations, K43N, M50F, A73L, Q206V, Y217K, N218S, Q271E, and the active site serine has been replaced with alanine to prevent autolysis. The purified Sbt70 folded spontaneously without the prodomain and crystallized at room temperature. Crystals of Sbt70 belong to space group P2(1)2(1)2(1) with unit cell parameters a = 53.5 A, b = 60.3 A, and c = 83.4 A. Comparison of the refined structure with other high-resolution structures of subtilisin BPN' establishes that the conformation of Sbt70 is essentially the same as that previously determined for other calcium-independent forms and that of other wild-type subtilisin BPN' structures, all folded in the presence of the prodomain. These findings confirm the results of previous solution studies that showed subtilisin BPN' can be refolded into a native conformation without the presence of the prodomain [Bryan et al., Biochemistry 31:4937-4945, 1992]. The structure analysis also provides the first descriptions of four stabilizing mutations, K43N, A73L, Q206V, and Q271E, and provides details of the interaction between the enzyme and the Ala-Leu-Ala-Leu tetrapeptide found in the active-site cleft.

Crystal structure of calcium-independent subtilisin BPN' with restored thermal stability folded without the prodomain

The three-dimensional structure of a subtilisin BPN' construct that was produced and folded without its prodomain shows the tertiary structure is nearly identical to the wild-type enzyme and not a folding intermediate. The subtilisin BPN' variant, Sbt70, was cloned and expressed in Escherichia coli without the prodomain, the 77-residue N-terminal domain that catalyzes the folding of the enzyme into its native tertiary structure. Sbt70 has the high-affinity calcium-binding loop, residues 75 to 83, deleted. Such calcium-independent forms of subtilisin BPN' refold independently while retaining high levels of activity [Bryan et al., Biochemistry, 31:4937-4945, 1992]. Sbt70 has, in addition, seven stabilizing mutations, K43N, M50F, A73L, Q206V, Y217K, N218S, Q271E, and the active site serine has been replaced with alanine to prevent autolysis. The purified Sbt70 folded spontaneously without the prodomain and crystallized at room temperature. Crystals of Sbt70 belong to space group P2(1)2(1)2(1) with unit cell parameters a = 53.5 A, b = 60.3 A, and c = 83.4 A. Comparison of the refined structure with other high-resolution structures of subtilisin BPN' establishes that the conformation of Sbt70 is essentially the same as that previously determined for other calcium-independent forms and that of other wild-type subtilisin BPN' structures, all folded in the presence of the prodomain. These findings confirm the results of previous solution studies that showed subtilisin BPN' can be refolded into a native conformation without the presence of the prodomain [Bryan et al., Biochemistry 31:4937-4945, 1992]. The structure analysis also provides the first descriptions of four stabilizing mutations, K43N, A73L, Q206V, and Q271E, and provides details of the interaction between the enzyme and the Ala-Leu-Ala-Leu tetrapeptide found in the active-site cleft.

Engineering the independent folding of the subtilisin BPN' prodomain: analysis of two-state folding versus protein stability

In complex with subtilisin BPN', the 77 amino acid prodomain folds into a stable compact structure comprising a four-stranded antiparallel beta-sheet and two three-turn alpha-helices. When isolated from subtilisin, the prodomain is 97% unfolded even under optimal folding conditions. Traditionally, to study stable proteins, denaturing cosolvents or temperatures are used to shift the equilibrium from folded to unfolded. Here we manipulate the folding equilibrium of the unstable prodomain by introducing stabilizing mutations generated by design. By sequentially introducing three stabilizing mutations into the prodomain we are able to shift the equilibrium for independent folding from 97% unfolded to 65% folded. Spectroscopic and thermodynamic analysis of the folding reaction was carried out to assess the effect of stability on two-state behavior and the denatured state. The denatured states of single and combination mutants are not discernably different in spite of a range of DeltaGunfolding from -2.1 to 0.4 kcal/mol. Conclusions about the nature of the denatured state of the prodomain are based on CD spectral data and calorimetric data. Two state folding is observed for a combination mutant of marginal stability (DeltaG = 0). Evidence for its two-state folding is based on the observed additivity of individual mutations to the overall DeltaGunfolding and the conformity of DeltaGunfolding vs T to two-state assumptions as embodied in the Gibbs-Helmholz equation. We believe our success in stabilizing the two-state folding reaction of the prodomain originates from the selection of mutations with improved ability to fold subtilisin rather than selection for increase in secondary structure content. The fact that a small number of mutations can stabilize the independent folding of the prodomain implies that most of the folding information already exists in the wild-type amino acid sequence in spite of the fact that the unfolded state predominates.

Streptomyces griseus aminopeptidase: X-ray crystallographic structure at 1.75 A resolution

The X-ray crystal structure of the enzyme Streptomyces griseus aminopeptidase (SGAP) has been determined in its double zinc form to 1.75 A resolution, in its apo-enzyme from (zinc removed) to 2.1 A resolution, and as a mercury replaced derivative to 2.1 A resolution. The structure solution was achieved by single isomorphous replacement with phasing from anomalous scattering (SIRAS), followed by density modification with histogram matching. The protein consists of a central beta-sheet made up of eight parallel and antiparallel strands, surrounded by helices on either side. The active site is located at the carbonyl ends of two middle strands of the beta-sheet region. Two sections of the chain that could not be traced were Glu196 to Arg202, which borders the active site, and the final seven C-terminal residues starting with Gly278. The active site contains two zinc cations, each with similar ligands, at a distance of 3.6 A from each other. An unknown molecule appears to be bound to both zinc ions in the active site at partial occupancy and has been modelled as a phosphate ion. A calcium binding site has also been identified, consistent with the observations that calcium modulates the activity of the enzyme, and increases its heat stability. The mechanism by which the calcium cation modulates enzyme activity is not apparent, since the location of the calcium binding site is approximately 25 A distant from the active site zinc ions. Comparison of the structure of SGAP to other known aminopeptidases shows that the enzyme is most similar to Aeromonas proteolytica aminopeptidase (AAP). Both enzymes share a similar topology, although the overall sequence identity is very low (24% in aligned regions). The coordination of the two active site zinc cations in SGAP resembles that of AAP. These two microbial enzymes differ from bovine lens leucine aminopeptidase (LAP) in both overall structure and in coordination of the two zinc ions.

Catalysis of a protein folding reaction: mechanistic implications of the 2.0 A structure of the subtilisin-prodomain complex

Biosynthesis of subtilisin is dependent on a 77 amino acid, N-terminal prodomain, which is autocatalytically processed to create the mature form of the enzyme [Ikemura, H., Takagi, H., & Inouye, M. (1987) J. Biol. Chem. 262, 7859-7864]. In order to better understand the role of the prodomain in subtilisin folding, we have determined the structure of the processed complex between the prodomain and subtilisin Sbt-70, a mutant engineered for facilitated folding. The prodomain is largely unstructured by itself but folds into a compact structure with a four-stranded antiparallel beta-sheet and two three-turn alpha-helices when complexed with subtilisin. The Ka of the complex is 2 x 10(8) M-1 at 25 degrees C. The prodomain binds on subtilisin's two parallel surface alpha-helices and supplies caps to the N-termini of the two helices. The C-terminal strand of the prodomain binds in the subtilisin substrate binding cleft. While Sbt-70 is capable of independent folding, the prodomain accelerates the process by a factor of > 10(7) M-1 of prodomain in 30 mM Tris-HCl, pH 7.5, at 25 degrees C. X-ray structures of the mutant subtilisin folded in vitro either with or without the prodomain are compared and show that the identical folded state is achieved in either case. A model of the folding reaction of Sbt-70 and the prodomain is described as the following equilibria: P + Su<-->Pf--SI<-->Pf--Sf, where Su and P are Sbt-70 and prodomain, respectively, which are largely unstructured at the start of the reaction, Pf--SI is a collision complex of a partially folded Sbt-70 and folded prodomain, and Pf--Sf is the complex of folded Sbt-70 and prodomain.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallization and preliminary crystallographic analysis of sfericase. A Bacillus sphaericus calcium-dependent serine proteinase

Sfericase is an important intracellular proteinase produced by Bacillus sphaericus in the stationary phase of growth. It is a Ca(2+)-dependent serine proteinase with optimal activity at pH 9.0 to 9.3. The molecular mass of sfericase is 32 kDa, as determined by sedimentation equilibrium. It seems to be involved in the interplay of various elements of the mosquitocidal activity of B. sphaericus, and hence is important for biological mosquito control. Sfericase significantly reduces viscosity of human pathological bronchial secretions and has recently shown good clinical effects in treatment of bronchitis, pneumonia and sinusitis. This enzyme was isolated from B. sphaericus and single crystals were obtained by the hanging drop vapor diffusion method. The crystals belong to the monoclinic space group P2, with cell dimensions of a = 46.94 A, b = 64.55 A, c = 86.23 A and beta = 95.4 degrees. These crystals are mechanically strong, they are stable in the X-ray beam and they diffract to better than 1.8 A resolution. The cell dimensions are consistent with four molecules per unit cell and two molecules in the asymmetric unit. A complete native data set to 1.77 A resolution has been collected on a Rigaku R-AXIS-IIc Imaging Plate Detector system and a heavy-atom derivative search is presently in progress.

Crystallization and preliminary crystallographic analysis of Streptomyces griseus aminopeptidase

Streptomyces griseus excretes a small molecular mass (30 kDa) aminopeptidase that could be used for various biotechnological applications. This enzyme was isolated from an extracellular protease mixture of Streptomyces griseus (Pronase E. Sigma) and single crystals were obtained by the vapor diffusion method using polyethylene glycol 4000 as the precipitant. The crystals belong to the tetragonal space group P4(1)2(1)2 (P4(3)2(1)2), with cell dimensions of a = b = 61.82(3) A and c = 145.88(4) A. These crystals are mechanically strong, they are stable in the X-ray beam and they diffract to better than 1.8 A resolution. The cell dimensions and the cell symmetry are consistent with one molecule in the asymmetric unit and the crystals are suitable for a detailed high-resolution crystallographic analysis. A complete native data set to 1.9 A resolution has been collected on a Rigaku R-AXIS-IIC Imaging Plate Detector system and a heavy-atom derivative search is in progress.

The composition and organization of photosystem I

Photosystem I, extensively studied in the past decade, was shown to be homologous in all photosynthetic organisms of the higher plants type. Its core complex was found to be highly conserved through evolution from cyanobacteria to higher plants. The genes coding for the subunits of CCI were isolated and the resulting sequences provided information about secondary structural elements. These suggested secondary structures enabled the prediction of the topology of these subunits in the photosynthetic membrane. Structural studies using both electron microscopy and X-ray crystallography, on isolated particles as well as on the complexes in the photosynthetic membrane, led to a better understanding of the overall structure of CCI. Recently two forms of three dimensional crystals of CCI were obtained. These crystals contain all the original components of CCI (both protein and pigments); these components have not been altered by crystallization. It is expected that a detailed crystallographic analysis of these crystals, together with biochemical, spectroscopical and molecular biology studies, will eventually lead to the elucidation of the high resolution structure of the photosystem I core complex and to the understanding of the exact role and mode of action of this complex in the photosynthetic membrane.

Monomeric and trimeric forms of photosystem I reaction center of Mastigocladus laminosus: crystallization and preliminary characterization

Photosystem I (PSI) reaction centers (RCs) of the thermophilic cyanobacterium Mastigocladus laminosus were purified and characterized. The PSI RC was obtained in two forms, monomeric and trimeric. The two forms contained the same number of pigments per P700 and displayed similar photochemical activities. The two forms had nearly identical polypeptide subunit compositions; the only observed difference was an additional subunit of about 12 kDa observed in the trimeric form. The purified preparations of both the monomeric and the trimeric forms were used for crystallization and preliminary crystallographic analysis. The trimeric PSI RC preparations produced several three-dimensional crystal forms, one of which, the "hexagonal needle" form (THN), had a hexagonal unit cell with dimensions of 300 x 300 x 160 A, containing four PSI RC trimers. The monomeric preparations also produced single crystals of several forms under various crystallization conditions. One of these crystal forms, the "hexagonal plate" (MHP), diffracted to a resolution of about 5.5 A. It had a hexagonal unit cell with dimensions of 192 x 192 x 163 A, containing six PSI RC monomers. Comparison of the PSI RCs in the crystals with those in the precrystallization preparations demonstrated that neither the monomeric nor the trimeric form of PSI RC was altered by the crystallization process. Both forms retained their original polypeptide subunit composition and their pigment content.