Association of Vitamin D Deficiency and Vitamin D Receptor Gene Polymorphisms with Type 1 Diabetes Risk: A South Indian Familial Study

Objective

Vitamin D is a potent immune modulator and is associated with autoimmune diseases, including type 1 diabetes (T1D). The vitamin D levels and its receptor gene polymorphisms together in T1D are not yet investigated in the South Indian population. The present study focused on exploring the significance of vitamin D levels and vitamin D receptor (VDR) gene polymorphisms with the risk of developing T1D in the South Indian population.

Methods

Patients with T1D and unaffected first-degree relatives (FDRs) were included in this study. Genotyping of VDR polymorphisms at four different loci (FokI- F/f, BsmI- B/b, TaqI- T/t, and ApaI- A/a) was assessed through the amplification refractive mutation system-polymerase chain reaction method. Serum vitamin D levels were measured in 98 T1D patients and 75 age- and sex-matched siblings.

Results

A total of 120 patients with T1D and 214 FDRs were included. Vitamin D deficiency (VDD) was observed in a higher proportion of T1D patients than in controls (52% vs. 32%; p<0.03). The frequency of the FokI-FF genotype was significantly higher [odds ratio (OR)=1.66; p<0.03] in T1D patients conferring a susceptible association with the disease. Nevertheless, the increased frequency of heterozygous Ff genotype (OR=0.57; p<0.02) among controls may confer a protective association with T1D. Furthermore, the transmission disequilibrium test revealed over-transmission of ApaI-A (T: U=15/5; p<0.006) and BsmI-B alleles (T: U=17/5; p<0.01) and under-transmission of BsmI-b/ApaI-a/TaqI-T haplotype (T: U=5.4/14.4; p=0.04) from parents to T1D patients.

Conclusion

The present study concludes that VDD is the major contributing risk factor to T1D development in the South Indian population. Furthermore, the FokI-FF genotype, BsmI-B, and ApaI-A alleles were positively associated with T1D. In contrast, the FokI-Ff genotype and BsmI-b/ApaI-a/TaqI-T haplotype were negatively associated with T1D.

Vitamin D Receptor Polymorphisms in a Spanish Cohort of Parkinson's Disease Patients

Background: Vitamin D receptor (VDR) is a nuclear hormone receptor widely expressed in the substantia nigra. Its association with an increased risk of Parkinson's disease (PD) is based on vitamin D deficiency and/or different polymorphisms in its gene receptor. This fact has been demonstrated by several case-control studies. Materials and Methods: Consequently, we investigated the association between VDR ApaI, BsmI, FokI, and TaqI gene polymorphisms and PD in a Spanish cohort that included 54 cases and 17 healthy controls. The detection of single nucleotide polymorphisms (SNPs) was performed using a polymerase chain reaction-restriction fragment length polymorphism. Results: Our data indicate that the SNPs were not associated with the age of onset of PD, nor with the occurrence of motor symptoms. However, only BsmI polymorphism was significantly associated with PD in this Spanish cohort. In fact, BsmI genotype was five times higher among PD patients than among controls, and the A allele was considered as a genetic risk for PD. Additionally, the combination of FokI and BsmI polymorphisms was significantly associated with PD and could represent a risk factor. Conclusion: We conclude that ApaI, TaqI, and FokI polymorphisms were not associated with PD, but BsmI could be a risk factor for PD in this randomized population.

Association Between Circulating 25-Hydroxy Vitamin D Receptor and Molecular Response in Multiple Myeloma

<b>Background and Objective:</b> Vitamin D Receptor (VDR) regulate several body processes related to metabolism, immunological function and oncogenesis. Low vitamin D levels are recognized as associated with a higher incidence of hematologic malignancies and poor outcomes. This study aims to determine whether vitamin D levels and VDR contribute to multiple myeloma (MM). <b>Materials and Methods:</b> This study enrolled twenty-five patients diagnosed with MM. Ages and gender were matched between patients and healthy groups. Serum Protein Electrophoresis (SPEP) was detected for all patients. Also, serum 25-hydroxy vitamin D levels were recorded. The PCR products were submitted to Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) and Sanger sequencing to detect VDR gene polymorphism including (FokI, ApaI and Tru9I). <b>Results:</b> This study revealed that an M spike was detected in five patients newly diagnosed with MM. According to vitamin D levels 84% of patients had a vitamin D deficiency. In the RFLP technique, FokI CT, ApaI AA and Tru9I GG genotypes were highly distributed in patients. Additionally, the MM group had a significant frequency of the T allele in the FokI (44.0%), the A allele in the ApaI (68.0%) and the A allele in the Tru9I (30.0%). <b>Conclusion:</b> The SPEP is an easy-to-perform laboratory test that can be used to detect and quantify monoclonal proteins. Low vitamin D level of less than 20 ng mL¹ is associated with an increased prevalence of MM and a worse response to treatment. In addition, VDR gene polymorphisms may be a molecular marker of MM risk.

ANALYSIS OF THE BLOOD HYPERCOAGULATION RISK IN PATIENTS WITH ISCHEMIC ATHEROTHROMBOTIC STROKE DEPENDING OF THE VDR GENE POLYMORPHISMS

OBJECTIVE

Aim: of our study was the analysis of the blood hypercoagulation risk in patients with ischemic atherotrombotic stroke depending of the VDR gene polymorphisms.

PATIENTS AND METHODS

Materials and Methods: Blood of 170 patients with ischemic atherothrombotic stroke (IATS) and 124 healthy individuals (control group) was used for genotyping. Four polymorphisms (FokI, BsmI, ApaI, TaqI) of gene VDR were examined with PCR-RFLP methodology. Statistical analysis was performed by using SPSS-17.0 program.

RESULTS

Results: Among patients with IATS who are carriers of the f/f genotype, FokI polymorphism of VDR gene by high thrombin time and a decrease in the rate of spontaneous fibrinolysis was registered. In individuals with the B/B genotype homozygous for the polymorphic variant, BsmI had significantly lower mean values of prothrombin and thrombin time and increased the rate of spontaneous fibrinolysis. The homozygotes for the A-allele ApaI polymorphism have 2.7 times higher risk of developing blood hypercoagulation than homozygotes for the a-allele was found.

CONCLUSION

Conclusions: Biochemical signs of hypercoagulation syndrome among patients with IATS who are carriers of the f/f genotype of the FokI polymorphic variant and among B/B homozygotes of the BsmI polymorphic variant and homozygotes for the A-allele of the AрaI polymorphism of the VDR gene were registered.

Base-Promoted (3 + 2) Cycloaddition of Trifluoroacetohydrazonoyl Chlorides with Imidates En Route to Trifluoromethyl-1,2,4-Triazoles

A base-mediated (3 + 2) cycloaddition of trifluoroacetohydrazonoyl chlorides with imidates for the construction of 3-trifluoromethyl-1,2,4-triazoles has been described. This reaction is characterized by readily starting materials, simple reaction conditions, good yields, a broad substrate scope, and excellent regioselectivity. The utility of this protocol has been validated by the synthesis of a drug-like molecule.

5Apal, Taql, Fokl, and Bsml polymorphisms and the susceptibility of Behcet's disease: an updated meta-analysis

OBJECTIVE

The aim of this study was to investigate whether the gene polymorphisms of vitamin D receptor (VDR) had a genetic effect on the susceptibility of Behcet's disease (BD).

MATERIAL AND METHODS

We conducted a meta-analysis emphasizing the association between the VDR gene polymorphisms and the risk of BD. The strength of the association in five genetic models was assessed by pooled odds ratios (OR) with a corresponding 95%confidence interval (CI).

RESULTS

A total of seven independent comparisons with 478 cases and 666 healthy controls were included in this meta-analysis. The overall results suggested that a significant association between ApaI polymorphism and BD risk was found in allele comparison, recessive model, and homozygote model among total populations. Subgroup analysis indicated that a significant association of ApaI polymorphism in the development of BD existed under the allelic model among Africans, while for Caucasians, a similar link was identified in the recessive model and homozygote model. Regarding Bsml polymorphism, an obvious relationship was detected to be significant in allele comparison and recessive model in the Caucasian population. Interestingly, the Fokl variant decreased the risk of BD in Africans under five genetic models, while it increased the risk in Caucasians across the recessive model and homozygote model.

CONCLUSION

The results of this meta-analysis provide evidence of the link between the four widely studied polymorphisms in the VDR gene and BD, indicating a robust estimate of the genetic risk.

SHIMS 3.0: Highly efficient single-haplotype iterative mapping and sequencing using ultra-long nanopore reads

The reference sequence of structurally complex regions can only be obtained through a highly accurate clone-based approach that we call Single-Haplotype Iterative Mapping and Sequencing (SHIMS). In recent years, improvements to SHIMS have reduced the cost and time required by two orders of magnitude, but internally repetitive clones still require extensive manual effort to transform draft assemblies into reference-quality finished sequences. Here we describe SHIMS 3.0, using ultra-long nanopore reads to augment the Illumina data from SHIMS 2.0 assemblies and resolve internally repetitive structures. This greatly minimizes the need for manual finishing of Illumina-based draft assemblies, allowing a small team with no prior finishing experience to sequence challenging targets with high accuracy. This protocol proceeds from clone-picking to finished assemblies in 2 weeks for about $80 (USD) per clone. We recently used this protocol to produce reference sequence of structurally complex palindromes on chimpanzee and rhesus macaque X chromosomes. Our protocol provides access to structurally complex regions that would otherwise be inaccessible from whole-genome shotgun data or require an impractical amount of manual effort to generate an accurate assembly.

Optimization of Heterologous Glucoraphanin Production In Planta

Glucoraphanin is a plant specialized metabolite found in cruciferous vegetables that has long been a target for production in a heterologous host because it can subsequently be hydrolyzed to form the chemopreventive compound sulforaphane before and during consumption. However, previous studies have only been able to produce small amounts of glucoraphanin in heterologous plant and microbial systems compared to the levels found in glucoraphanin-producing plants, suggesting that there may be missing auxiliary genes that play a role in improving production in planta. In an effort to identify auxiliary genes required for high glucoraphanin production, we leveraged transient expression in Nicotiana benthamiana to screen a combination of previously uncharacterized coexpressed genes and rationally selected genes alongside the glucoraphanin biosynthetic pathway. This strategy alleviated metabolic bottlenecks, which improved glucoraphanin production by 4.74-fold. Our optimized glucoraphanin biosynthetic pathway provides a pathway amenable for high glucoraphanin production.

Influence of sequential exogenous pretreatment and contact ultrasound-assisted air drying on the metabolic pathway of glucoraphanin in broccoli florets

In this investigation, the combinations of exogenous pretreatment (melatonin or vitamin C) and contact ultrasound-assisted air drying were utilized to dry broccoli florets. To understand the influences of the studied dehydration methods on the conversion of glucoraphanin to bioactive sulforaphane in broccoli, various components (like glucoraphanin, sulforaphane, myrosinase, etc.) and factors (temperature and moisture) involved in the metabolism pathway were analyzed. The results showed that compared with direct air drying, the sequential exogenous pretreatment and contact ultrasound drying shortened the drying time by 19.0-22.7%. Meanwhile, contact sonication could promote the degradation of glucoraphanin. Both melatonin pretreatment and vitamin C pretreatment showed protective effects on the sulforaphane content and myrosinase activity during the subsequent drying process. At the end of drying, the sulforaphane content in samples dehydrated by the sequential melatonin (or vitamin C) pretreatment and ultrasound-intensified drying was 14.4% (or 26.5%) higher than only air-dried samples. The correlation analysis revealed that the exogenous pretreatment or ultrasound could affect the enzymatic degradation of glucoraphanin and the generation of sulforaphane through weakening the connections of sulforaphane-myrosinase, sulforaphane-VC, and VC-myrosinase. Overall, the reported results can enrich the biochemistry knowledge about the transformation of glucoraphanin to sulforaphane in cruciferous vegetables during drying, and the combined VC/melatonin pretreatment and ultrasound drying is conducive to protect bioactive sulforaphane in dehydrated broccoli.

Effect of selenium-sulfur interaction on the anabolism of sulforaphane in broccoli

The effects of S (as sulphate) and Se (as selenite) treatment (S mM/Se μM: 1/0, 1/50, 1/100, 1/150, 4/0, 4/50, 4/100, and 4/150) on the production of sulforaphane (an anticancer compound), the accumulation of its precursor substance, and the expression of genes related to glucoraphanin biosynthesis in broccoli were examined. Sulforaphane yield and myrosinase activity increased significantly with the combined application of 4 mM S and 100 μM Se on broccoli. Furthermore, the concentrations of glucoraphanin (a sulforaphane precursor) and methionine (a glucoraphanin substrate) slightly changed after Se application. And the strong anticancer activity of compound Se-SMC was further improved. Analysis of related gene expression showed that MY, which encodes myrosinase, was strongly induced by Se treatment. Thus, the myrosinase activity induced by Se treatment is the dominant factor affecting sulforaphane yield from glucoraphanin hydrolyzation. Selenium-sulfur biofortification provides a technical support for the cultivation of broccoli with high sulforaphane and high anti-cancer selenium compounds.

Molecular Cloning, Expression Pattern and Genotypic Effects on Glucoraphanin Biosynthetic Related Genes in Chinese Kale (Brassica oleracea var. alboglabra Bailey)

Glucoraphanin is a plant secondary metabolite that is involved in plant defense and imparts health-promoting properties to cruciferous vegetables. In this study, three genes involved in glucoraphanin metabolism, branched-chain aminotransferase 4 (BCAT4), methylthioalkylmalate synthase 1 (MAM1) and dihomomethionine N-hydroxylase (CYP79F1), were cloned from Chinese kale (Brassica oleracea var. alboglabra Bailey). Sequence homology and phylogenetic analysis identified these genes and confirmed the evolutionary status of Chinese kale. The transcript levels of BCAT4, MAM1 and CYP79F1 were higher in cotyledon, leaf and stem compared with flower and silique. BCAT4, MAM1 and CYP79F1 were expressed throughout leaf development with lower transcript levels during the younger stages. Glucoraphanin content varied extensively among different varieties, which ranged from 0.25 to 2.73 µmol·g(-1) DW (dry weight). Expression levels of BCAT4 and MAM1 were high at vegetative-reproductive transition phase, while CYP79F1 was expressed high at reproductive phase. BCAT4, MAM1 and CYP79F1 were expressed significantly high in genotypes with high glucoraphanin content. All the results provided a better understanding of the roles of BCAT4, MAM1 and CYP79F1 in the glucoraphanin biosynthesis of Chinese kale.

Evaluating the impact of sprouting conditions on the glucosinolate content of Brassica oleracea sprouts

The glucosinolates content of brassica plants is a distinctive characteristic, representing a healthy advantage as many of these compounds are associated to antioxidant and anti-carcinogenic properties. Brassica sprouts are still an underutilized source of these bioactive compounds. In this work, four varieties of brassica sprouts (red cabbage, broccoli, Galega kale and Penca cabbage), including two local varieties from the North of Portugal, were grown to evaluate the glucosinolate profile and myrosinase activity during the sprouting. Also the influence of light/darkness exposure during sprouting on the glucosinolate content was assessed. Glucosinolate content and myrosinase activity of the sprouts was evaluated by HPLC methods. All sprouts revealed a higher content of aliphatic glucosinolates than of indole glucosinolates, contrary to the profile described for most of brassica mature plants. Galega kale sprouts had the highest glucosinolate content, mainly sinigrin and glucoiberin, which are recognized for their beneficial health effects. Penca cabbage sprouts were particularly richer in glucoraphanin, who was also one of the major compounds in broccoli sprouts. Red cabbage showed a higher content of progoitrin. Regarding myrosinase activity, Galega kale sprouts showed the highest values, revealing that the use of light/dark cycles and a sprouting phase of 7-9 days could be beneficial to preserve the glucosinolate content of this variety.

Generation of Se-fortified broccoli as functional food: impact of Se fertilization on S metabolism

Selenium (Se)-fortified broccoli (Brassica oleracea var. italica) has been proposed as a functional food for cancer prevention, based on its high glucosinolate (GSL) content and capacity for Se accumulation. However, as selenate and sulphate share the initial assimilation route, Se fertilization could interfere with sulphur metabolism and plant growth. Consequently, GSL accumulation could be compromised. To evaluate these potentially adverse effects of Se fertilization, we performed a comprehensive study on sand-grown young broccoli plants (weekly selenate applications of 0.8 µmol plant(-1) via the root) and field-grown adult broccoli plants during head formation (single foliar selenate application: 25.3 or 253 µmol plant(-1) ). The results show that under these conditions, Se application does not affect plant growth, contents of cysteine, glutathione, total GSL, glucoraphanin (major aliphatic GSL) or the expression of BoMYB28 (encoding a functionally confirmed master regulator for aliphatic GSL biosynthesis). Conversely, due to the changed expression of sulphate transporters (BoSULTR1;1, 1;2, 2;1, and 2;2), sulphate and total S contents increased in the shoot of young plants while decreasing in the root. We conclude that broccoli can be fertilized with Se without reduction in GSL content, even with Se accumulation exceeding the level recommended for human consumption.

Direct quantitation of glucoraphanin in dog and rat plasma by LC-MS/MS

A rapid method to quantify levels of the beta-thioglycoside N-hydroxyl sulfate, glucoraphanin, in dog and rat plasma to support pre-clinical toxicological and pharmacological studies has been developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Glucoraphanin was extracted from plasma by protein precipitation with acetonitrile and separated via hydrophilic interaction liquid chromatography (HILIC) using a Luna 5microm Silica (2) 100A column (50mmx2.0mm) at a flow rate of 0.3mL/min. Solvent A consisted of 200mM ammonium acetate and formic acid (99:1, v/v) and Solvent B was acetonitrile. Initial conditions (90% Solvent B) were held for 0.01min after injection, decreased to 40% in 0.5min and held constant for 2.5min, returning to initial conditions for 3min (reequilibration time). Glucoraphanin was detected by MS/MS using a turbo ion spray interface as the ion source operating in negative ion mode. Acquisition was performed in multiple reaction monitoring mode at m/z 435.8-->96.7. The method was validated for the calibration range 10-2000ng/mL. Within- and between-run precision for the low, mid and high QC levels was 8% R.S.D. or less and accuracy ranged from 100 to 113%. The lower limit of quantification was 10ng/mL; calibration curves encompassed the range of plasma concentrations expected to be found in bioavailability and pharmacokinetics studies with glucoraphanin. The method has successfully been applied to the determination of glucoraphanin in dog and rat plasma and should be extendable to other species as well.

Engineering cell adhesive surfaces that direct integrin alpha5beta1 binding using a recombinant fragment of fibronectin

Integrin receptors mediate cell adhesion to extracellular matrices and trigger signals that direct cell function. While many integrins bind to the arginine-glycine-aspartic acid (RGD) motif present in numerous extracellular proteins, integrin alpha(5)beta(1) requires both the PHSRN synergy site in the 9th and the RGD site in the 10th type III repeat of fibronectin (FN). Binding of alpha(5)beta(1) to FN is critical to many cellular processes, including osteoblast and myoblast differentiation. This work focused on engineering integrin-specific bioadhesive surfaces by immobilizing a recombinant FN fragment (FNIII(7-10)) encompassing the alpha(5)beta(1) binding domains of FN. Model hybrid surfaces were engineered by immobilizing FNIII(7-10) onto passively adsorbed, non-adhesive albumin. Homo- and hetero-bifunctional crosslinkers of varying spacer-arm length targeting either the cysteine or lysine groups on FNIII(7-10) were investigated in ELISA and cell adhesion assays to optimize immobilization densities and activity. FN-mimetic surfaces presenting controlled densities of FNIII(7-10) were generated by varying the concentration of FNIII(7-10) in the coupling solution at a constant crosslinker concentration. Cells adhered to these functionalized surfaces via integrin alpha(5)beta(1) and blocking with integrin-specific antibodies completely eliminated adhesion. In addition, adherent cells spread and assembled focal adhesions containing alpha(5)beta(1), vinculin, and talin. This biomolecular engineering strategy represents a robust approach to increase biofunctional activity and integrin specificity of biomimetic materials.

Effect of 6-O-sulfonate hexosamine residue on anticoagulant activity of fully O-sulfonated glycosaminoglycans

Intact and fully O-sulfonated glycosaminoglycans (GAGs) including chondroitin sulfate, dermatan sulfate, hyaluronan, heparan sulfate and heparin were chemically de-O-sulfonated on their hexosamine C-6 position (6-O-desulfonation) using N,O-bis(trimethylsilyl) acetamide. 1H NMR spectroscopy and chemical compositional analysis showed that the chemical de-O-sulfonation at C-6 position of hexosamine residues in both intact and fully O-sulfonated GAGs was completely achieved. Since GAGs and their derivatives are often used as anticoagulant agents, their anti-amidolytic activities were determined. While most of anticoagulant activity of fully O-sulfonated GAGs (FGAGs) and heparin disappeared following chemical 6-O-desulfonation, the activity of 6-O-desulfonated fully O-sulfonated dermatan sulfate (De6FDS) remained. This observation suggests the importance of the position of O-sulfonate groups for anti-coagulant activity.

Rhenium-188-labeled anti-neural cell adhesion molecule antibodies with 2-iminothiolane modification for targeting small-cell lung cancer

We have evaluated the potential of 188Re-labeled monoclonal antibodies (MAbs) modified with 2-iminothiolane (2IT) for targeting small-cell lung cancer (SCLC). Radiolabeled MAbs NK1NBL1 and C218 recognizing neural cell adhesion molecule were injected i.v. into athymic mice inoculated with human SCLC tumors, and the biodistribution was examined. NK1NBL1 localized in the tumors better than C218. 188Re-labeled MAbs cleared from the blood faster than 125I-labeled counterparts, resulting in higher tumor-to-blood ratios. In conclusion, the 188Re-labeled MAbs are attractive candidates for imaging and therapy of SCLC.

Vitamin D receptor and estrogen receptor gene polymorphisms in postmenopausal Danish women: no relation to bone markers or serum lipoproteins

OBJECTIVE

To investigate the polymorphisms of the vitamin D receptor (VDR) and estrogen receptor (ER) genes in relation to biochemical markers of bone turnover (serum osteocalcin and urinary collagen type I degradation products (CrossLaps), and to study ER genotypes in relation to serum lipoproteins, blood pressure, or changes in these parameters after 2 years of hormone replacement therapy (HRT) in 499 Danish postmenopausal women.

METHODS

The VDR gene polymorphisms were determined by means of the three restriction enzymes, i.e. BsmI, ApaI and TaqI, while the ER gene polymorphisms were determined by means of the PvuII and XbaI restriction enzymes. Serum osteocalcin, urinary CrossLaps and the lipoproteins were also assessed. Body mass index was recorded.

RESULTS

The VDR or ER genotypes did not differ significantly with respect to age, age at menopause or body mass index. No significant effect of VDR or ER genotype on bone turnover was found. Furthermore, we were unable to find any relationship between ER genotype and lipoproteins or blood pressure at baseline, or changes in these parameters during HRT.

CONCLUSION

A clinically significant relationship between VDR and ER genotypes and biochemical markers of bone turnover or serum lipoproteins could not be demonstrated in healthy Danish postmenopausal women.

Nucleic acid-dependent cross-linking of the nucleocapsid protein of Sindbis virus

The assembly of the alphavirus nucleocapsid core is a multistep event requiring the association of the nucleocapsid protein with nucleic acid and the subsequent oligomerization of capsid proteins into an assembled core particle. Although the mechanism of assembly has been investigated extensively both in vivo and in vitro, no intermediates in the core assembly pathway have been identified. Through the use of both truncated and mutant Sindbis virus nucleocapsid proteins and a variety of cross-linking reagents, a possible nucleic acid-protein assembly intermediate has been detected. The cross-linked species, a covalent dimer, has been detected only in the presence of nucleic acid and with capsid proteins capable of binding nucleic acid. Optimum nucleic acid-dependent cross-linking was seen at a protein-to-nucleic-acid ratio identical to that required for maximum binding of the capsid protein to nucleic acid. Identical results were observed when cross-linking in vitro assembled core particles of both Sindbis and Ross River viruses. Purified cross-linked dimers of truncated proteins and of mutant proteins that failed to assemble were found to incorporate into assembled core particles when present as minor components in assembly reactions, suggesting that the cross-linking traps an authentic intermediate in nucleocapsid core assembly. Endoproteinase Lys-C mapping of the position of the cross-link indicated that lysine 250 of one capsid protein was cross-linked to lysine 250 of an adjacent capsid protein. Examination of the position of the cross-link in relation to the existing model of the nucleocapsid core suggests that the cross-linked species is a cross-capsomere contact between a pentamer and hexamer at the quasi-threefold axis or is a cross-capsomere contact between hexamers at the threefold axis of the icosahedral core particle and suggests several possible assembly models involving a nucleic acid-bound dimer of capsid protein as an early step in the assembly pathway.

Optimized conditions to couple two water-soluble biomolecules through alkylamine thiolation and thioetherification

A simple method for introducing, in buffered saline, a reactive sulfhydryl group on water-soluble molecules bearing an alkyl-amino group is described. This method is based on the use of two water-soluble reagents: 2-iminothiolane and 6,6'-dithiodinicotinic acid. The first one is open upon reaction with an amino group, and the generated thiol group is immediately protected by action of the second reagent. The optimal conditions were determined by taking into account the stability and the reactivity of both reagents with regards to pH and temperature. This method was validated through two applications, the substitution of bovine serum albumin with a bromoacetyl peptide and the substitution of an amino link at the 5' end of an oligonucleotide by reaction with either a fluorescent tag, iodoacetamidofluorescein, or a bromoacetyl peptide, upon reduction of the protected disulfide bridge with a third water-soluble reagent, namely tris(2-carboxyethyl)phosphine.

Characterisation of Listeria ivanovii isolates from the UK using pulsed-field gel electrophoresis

Forty-three Listeria ivanovii isolates were collected in the UK between 1991 and 1997 from: 35 animal infections; two human infections; five foods; and one environmental source. A further two type strains of L. ivanovii (subsp. ivanovii and subsp. londoniensis) were obtained from a culture collection. These bacteria were characterised by conventional phenotypic methods and by pulsed-field gel electrophoresis (PFGE) using ApaI and SmaI. Forty-two of the isolates from the UK were identified as L. ivanovii subsp. ivanovii and the remaining culture as L. ivanovii subsp. londoniensis. Six and four PFGE profiles were obtained using ApaI and SmaI digestion respectively; six composite profiles were obtained combining the results for both enzymes. The PFGE profile of the UK L. ivanovii subsp. londoniensis (isolated from processed shrimps) was similar to the type strain of this subspecies and differed from all of the L. ivanovii subsp. ivanovii tested. The majority of isolates (38 out of 45) belonged to one profile showing that the UK population of this bacterium is much less genetically diverse than similar studies have shown for Listeria monocytogenes.

Synthesis and assembly of the D1 protein into photosystem II: processing of the C-terminus and identification of the initial assembly partners and complexes during photosystem II repair

In previous studies [van Wijk, K. J., Bingsmark, S., Aro, E.-M., & Andersson, B. (1995) J. Biol. Chem. 270, 25685-25695; van Wijk, K. J., Andersson, B., & Aro, E.-M. (1996) J. Biol. Chem 271, 9627-9636], we have demonstrated that D1 protein synthesized in isolated chloroplasts and thylakoids is incorporated into the photosystem II (PSII) core complex. By pulse-chase experiments in these in vitro systems, followed by sucrose gradient fractionation of solubilized thylakoid membranes, it was shown that this assembly proceeded stepwise; first the D1 protein was incorporated to form a PSII reaction center complex (PSII rc), and through additional assembly steps the PSII core complex was formed. In this study, we have analyzed this assembly process in more detail, with special emphasis on the initial events, through further purification and analysis of the assembly intermediates by nondenaturing Deriphat-PAGE and by flatbed isoelectric focusing. The D2 protein was found to be the dominant PSII reaction center protein initially associating with the new D1 protein. This strongly suggests that the D2 protein is the primary "receptor" or stabilizing component during or directly after synthesis of the D1 protein. After formation of the D1-D2 heterodimer, cyt b559 became attached, whereas the psbI gene product was assembled as a subsequent step, thereby forming a PSII reaction center complex. Subsequent formation of the PSII core occurred by binding of CP47 and then CP43 to the PSII rc. The rapid radiolabeling of a minor population of a PSII core subcomplex without CP43 indicated that an association of newly synthesized D1 protein with a preexisting complex consisting of D2/cyt b55q/psbI gene product/CP47 was possibly occurring, in parallel to the predominant sequential assembly pathway. The kinetics of synthesis and processing of the precursor D1 protein were followed in isolated chloroplasts and were compared with its incorporation into PSII assembly intermediates. No precursor D1 protein was found in PSII core complexes, indicating either that incorporation into the PSII core complex facilitates the cleavage of the C-terminus or, more likely, that processing is more rapid than the assembly into the PSII core.

Human T cell leukemia virus type 1 tax protein increases NF-kappa B dimer formation and antagonizes the inhibitory activity of the I kappa B alpha regulatory protein

Human T cell leukemia virus type 1 (HTLV-1) encodes a strong transcriptional transactivator, the Tax protein, that stimulates viral transcription through the long terminal repeat and also stimulates many cellular genes via the activation of host transcription factors. Previous studies have demonstrated that Tax activates NF-kappa B through binding to the Rel homology domain of NF-kappa B proteins. Tax was also shown to increase degradation of I kappa B alpha resulting in the induction of NF-kappa B DNA binding activity. We addressed the specificity and function of Tax interaction with members of the NF-kappa B/I kappa B alpha family by using EMSA, protein affinity chromatography, protein-protein crosslinking and co-immunoprecipitation assays. The results of the present study demonstrate that: (1) Tax enhances NF-kappa B binding to DNA 40- to 100-fold by increasing NF-kappa B dimer formation which can be detected in the absence of DNA; (2) Tax binds to all NF-kappa B DNA binding subunits in vitro and to I kappa B alpha; (3) Tax physically associates with I kappa B alpha in vivo; and (4) Tax and I kappa B alpha have antagonistic effects on NF-kappa B binding and gene activity. These results suggest that Tax interaction with I kappa B alpha interferes with the formation of NF-kappa B-I kappa B alpha complexes and may play a role in targeting I kappa B alpha for degradation.

The F1F0-ATPase complex from bovine heart mitochondria: the molar ratio of the subunits in the stalk region linking the F1 and F0 domains

The F1 globular catalytic domain and the F0 intrinsic membrane domain of the F1F0-ATPases in bacteria, chloroplasts, and mitochondria are connected by a slender stalk. In the F1F0 complex from bovine heart mitochondria, the stalk is thought to contain subunits OSCP, d, and F6, and the globular part of the membrane bound subunit b, referred to as b'. It has been shown previously that the OSCP, b', d, and F6 proteins can be assembled in vitro into a water soluble complex named the "stalk". The stalk and F1-ATPase together form another complex named F1.stalk. In this paper, the molar ratios of the OSCP, b (or b'), d, and F6 in the stalk, F.stalk, and F1F0-ATPase complexes have been investigated by three independent methods. By quantitation of radioactivity incorporated by S-carboxymethylation with iodo-2-[14C]acetic acid into a stalk complex containing a form of F6 with the mutation Glu3-Cys, it was shown that the stalk consists of equimolar quantities of its four constituent proteins. In the stalk complex containing the natural F6 sequence, this conclusion was confirmed both by quantitation of radioactivity incorporated by Nepsilon-acetimidation with ethyl [1-14C]acetimidate, and by quantitative N-terminal sequence analysis of subunits. By similar Nepsilon-acetimidation experiments, it has been demonstrated that the F1.stalk complex contains one copy per assembly of the OSCP, b', d, and F6 proteins and that the F1F0-ATPase contains one copy per enzyme complex of subunits OSCP, b, and d. The presence of one copy per complex of the OSCP, b' (or b), d, and F6 proteins in the F1.stalk and F1F0-ATPase complexes, respectively, was confirmed by quantitative sequencing.

Protein-rRNA binding features and their structural and functional implications in ribosomes as determined by cross-linking studies

We have investigated protein-rRNA cross-links formed in 30S and 50S ribosomal subunits of Escherichia coli and Bacillus stearothermophilus at the molecular level using UV and 2-iminothiolane as cross-linking agents. We identified amino acids cross-linked to rRNA for 13 ribosomal proteins from these organisms, namely derived from S3, S4, S7, S14, S17, L2, L4, L6, L14, L27, L28, L29 and L36. Several other peptide stretches cross-linked to rRNA have been sequenced in which no direct cross-linked amino acid could be detected. The cross-linked amino acids are positioned within loop domains carrying RNA binding features such as conserved basic and aromatic residues. One of the cross-linked peptides in ribosomal protein S3 shows a common primary sequence motif--the KH motif--directly involved in interaction with rRNA, and the cross-linked amino acid in ribosomal protein L36 lies within the zinc finger-like motif of this protein. The cross-linked amino acids in ribosomal proteins S17 and L6 prove the proposed RNA interacting site derived from three-dimensional models. A comparison of our structural data with mutations in ribosomal proteins that lead to antibiotic resistance, and with those from protein-antibiotic cross-linking experiments, reveals functional implications for ribosomal proteins that interact with rRNA.

Labelling small quantities of monoclonal antibodies and their F(ab')2 fragments with technetium-99m

Addition of sulfhydryl groups with 2-iminothiolane (2-IT) is an important new method for labelling monoclonal antibodies (mAb) and fragments with 99mTc. F(ab')2 fragments were prepared by digestion of 1B7.11 and BCD-F9 with pepsin. Optimal conditions for labelling 20-100 micrograms mAb or F(ab')2 involved a 2000:1 molar ratio of 2-IT:protein in phosphate buffer pH 7.4 for 30 min followed by addition of 99mTc-pertechnetate and stannous glucoheptonate. Recovered yields were > 70% and radiochemical purities were > 90% with a total preparation time of < 90 min.

A homodimer represents an active species of the peptidyl-prolyl cis/trans isomerase FKBP25mem from Legionella pneumophila

The molecular mass of the native FK506-binding peptidyl-prolyl cis/trans isomerase (PPIase) FKBP25mem from Legionella pneumophila (Mip (macrophage infectivity potentiator) protein) was determined by two methods. By gel-permeation chromatography we found no indication of the presence of the monomeric enzyme. However, an oligomeric state with a molecular mass of about 62 kDa was detected. By cross-linking with dimethyl pimelimidate and subsequent SDS-PAGE of either the surface proteins of intact L. pneumophila cells or the purified recombinant FKBP25mem in solution, we observed an immunoreactive band indicative of a mass in the dimer range. In contrast to human recombinant FKBP12, the enzymatic activity of Legionella FKBP25men was strongly dependent on the protein concentration, pointing to a dimer as the most active species. However, the inhibition by FK506 yielded a nearly constant value of Ki of about 250 nM when measured in the same range of FKBP25mem concentration. These results may be explained by the fact that monomeric FKBP25mem has little, if any, influence on enzymatic activity when compared with the homodimer.

Self-association of the globular domain of histone H5

The capacity of the globular domain of the chicken erythrocyte linker histone H5 (GH5) to self-associate in solution has been demonstrated by chemical cross-linking with dimethyl 3,3'-dithiobis-(propionimidate) (DTBP), dithiobis(succinimidyl propionate) (DSP), and 3,3'-dithiobis(sulfosuccinimidyl propionate) (DTSSP). Several observations suggest that the GH5-GH5 interactions that mediate self-association are specific: (a) Incubation with each of the above reagents produces a discrete and characteristic pattern of cross-linked products; (b) GH1, the related peptide from chicken erythrocyte H1, is not cross-linked under the same conditions; (c) GH5 is not cross-linked with disuccinimidyl tartrate (DST), which has a shorter cross-linking span (6.4 A) than the other reagents (12 A); and (d) analysis of cross-linking as a function of peptide concentration provides an equilibrium constant for GH5 self-association of (4.8 +/- 1.3) x 10(3) M-1. The ability of GH5 to specifically self-associate is compatible with the proposal [Thoma, F., Koller, T., & Klug, A. (1979) J. Cell Biol. 83, 403-427] that linker histone globular domains occupy an axial position within the higher order chromatin fiber; the spatial juxtaposition of the GH5 domains at this location would be expected to promote their association and exert a stabilizing effect upon higher order chromatin structure.

2-Iminothiolane: a reagent for the introduction of sulphydryl groups into oligosaccharides derived from asparagine-linked glycans

A facile method for introducing reactive sulphydryl groups into oligosaccharides was developed. 1-Amino-oligosaccharides generated from asparagine-linked glycans by peptide-N4(N-acetyl-beta-D-glucosaminyl) asparagine amidase (PNGase F) digestion were monitored by high-performance anion-exchange chromatography with pulsed amperometric detection and derivatized under optimal conditions with 2-iminothiolane-HCl. The resulting mercapto-butyramido oligosaccharides, which were obtained in high yield, were alkylated with a fluorescent reagent and used to selectively assay for endoglycosidases that hydrolyse di-N-acetylchitobiose linkages.

Detection of fungal carbohydrate antigens by high-performance immunoaffinity chromatography using a protein A column with covalently linked immunoglobulin G

Fungal carbohydrate antigens were analysed by high-performance immunoaffinity chromatography (HPIAC) with immunoglobulin G (IgG) antibodies raised against extracellular polysaccharides of Mucor racemosus. The protein A-IgG complex was covalently bound with dimethyl pimelimidate, which enabled the use of strong acidic buffers to release the tightly bound antigens from the column. Prior to pulsed-amperometric detection, an anion-micromembrane suppressor was used to raise the pH of the effluent to above 12 without dilution. The HPIAC system provides a sophisticated method for the rapid and sensitive detection of antigenic oligomeric carbohydrates in biological samples and is proposed as an alternative to quantitative enzyme-linked immunosorbent assay techniques.

Semisynthetic fluorohydrolases prepared by chemical modification of ribonuclease

A process for conformational modification of protein, which we have previously reported, was investigated as a means of generating fluorohydrolase activity in bovine ribonuclease (RNase). The resulting modified RNase had catalytic activity that depended upon the chosen modifier. Bovine pancreatic ribonuclease, modified by addition of hexamethylphosphoramide (HMPA) at pH 3, was derivatized with diimidates of chain lengths from C1 to C8. The derivative with the highest activity was obtained when RNase was crosslinked with dimethyl pimelimidate (C5). This derivative, which was active over a pH range of 6.5 to 8.0 with an optimum pH of 7.4, hydrolyzed phenylmethylsulfonylfluoride (PMSF) and the potent acetylcholinesterase inhibitor, diisopropyl phosphorofluoridate (DFP). The mean fluorohydrolase activity for four preparations using dimethyl pimelimidate was 0.8 +/- 0.2 U mg-1. Gel filtration on G-75 Sephadex and SDS-polyacrylamide gel electrophoresis showed components having a molecular weight of 13,000 and 27,000, with activity restricted to the 27,000 molecular weight fraction. After gel filtration, the specific activity was 9.1 +/- 2.4 U mg-1, resulting in a molecular activity of 125 min-1. The mechanism of this unique transformation of RNase into a fluorohydrolase is not known, nor has the location of the active site been determined.

Protein topography of Sulfolobus solfataricus ribosomes by cross-linking with 2-iminothiolane. Sso L12e, Sso L10e, and Sso L11e are neighbors

Large ribosomal subunits from Sulfolobus solfataricus were cross-linked with 2-iminothiolane in order to investigate the arrangement of proteins in the region containing the multicopy acidic protein Sso L12e, the protein homologous to Escherichia coli L7/L12. Proteins from cross-linked 50 S subunits were extracted and fractionated by chromatography on CM-cellulose. Fractions containing Sso L12e were analyzed by "diagonal" (two-dimensional reducing/nonreducing) dodecyl sulfate polyacrylamide gel electrophoresis. Sso L12e appeared in cross-linked homodimers and also in cross-linked complexes that contained Sso L10e, the protein equivalent to E. coli L10. In addition, Sso L12e was found in cross-links to L4, L6a, L26, and L29. N-terminal sequences obtained for L6a and L26 showed them to have significant homologies to E. coli proteins L11 and L23, respectively. The results indicate the presence in this archaebacterial ribosome of Sso L12e dimers and their location near Sso L10e and Sso L11e. The Sso L12e-L29 (Sso L23e) cross-link suggests proximity between components of the factor-binding and peptidyltransferase domains, since E. coli L23 is a protein affinity-labeled by puromycin. The (Sso L12e)4-Sso L10 pentameric complex, identified previously from studies in solution, appears to represent correctly the arrangement of these proteins in the ribosome. The occurrence in the archaebacterial ribosome of this unique structural element, similar to those shown previously in eubacteria and eukaryotes, reinforces the concept that the protein quaternary structure of the ribosomal factor-binding domain is highly conserved.

Dimerization of the chicken progesterone receptor in vitro can occur in the absence of hormone and DNA

We have analyzed the dimerization of two forms of the chicken progesterone receptor (cPRA and cPRB) by nondenaturing gradient gel electrophoresis and chemical cross-linking with dimethylpimelimidate (DMP). We demonstrate by these two methods that the PRs assemble in vitro into dimers in the absence of DNA, and that dimerization does not require hormone. The cPRA homodimer binds quantitatively to its cognate DNA response element in our nondenaturing gradient gel assay. DMP cross-linking confirms that both forms of the receptor (cPRA and cPRB) assemble into dimers in solution. Finally, in a standard mobility shift assay, chemically cross-linked receptors bind to the progesterone DNA response element with high affinity. We conclude that the PR contains a dimerization motif, which can promote stable subunit-subunit contacts without the presence of hormone in vitro. The complex thus formed expresses sequence-specific DNA-binding activity indistinguishable from that observed in the presence of hormone.

Analysis of U1snRNP-specific A protein cross-linked complexes

The organization of the U1snRNP-specific A protein (34 kDa) has been analyzed by 12 and 16 A thiol-reversible chemical cross-linking and Western blotting. A-containing cross-linked complexes had molecular masses of 43, 47, 56, 62, 67, 105 and 125 kDa. None of these complexes could be cross-linked following ribonuclease digestion, suggesting that UsnRNA may play important roles in the spatial organization of A and other proteins. Moreover, the data suggest that A is proximal to, and may have interactions with, UsnRNP-specific proteins C and 70 kDa as well as with UsnRNP-common proteins B, E and G.

Immunotoxin construction with a ribosome-inactivating protein from barley

The aim of this study was to determine the suitability of a ribosome-inactivating protein (RIP) from barley endosperm for use as an immunotoxin. This barley RIP is identical with the 30-kDa protein first reported by Coleman and Roberts [(1982) Biochim. Biophys. Acta 696, 239] and sequenced by Asano and co-workers [(1986) Carlsberg Res. Commun. 51, 75]. Use of the terms barley toxin I, II, and III is proposed to describe the three isoforms resolved by cation-exchange chromatography. An improved procedure for isolating the protein involving the steps of aqueous extraction, ammonium sulfate precipitation, and cation-exchange HPLC is described. Barley toxin II retained activity after exposure to ca. 40% acetonitrile and 0.1% trifluoroacetic acid or lyophilization. In a comparative study using the rabbit reticulocyte lysate assay, the protein was about 68% and 30% as potent as gelonin and ricin A-chain (RTA), respectively. Introduction of SH groups with 2-iminothiolane resulted in a substantial loss of activity as the number of thiol groups approached four. Therefore, it was necessary to limit thiolation to an average of one to two SH groups per toxin molecule. Anti-transferrin receptor-based immunotoxins constructed with RTA, gelonin, and barley toxin II exhibited comparable cytotoxicity against a human colon tumor cell line. We conclude that the availability of raw material, ease of purification, and stability of barley toxin II to lyophilization and denaturing conditions render it a suitable protein for the construction of immunotoxins.

Asymmetric distribution of the phosphatidylinositol-linked phospho-oligosaccharide that mimics insulin action in the plasma membrane

We have investigated the topography of a glycosyl-phosphatidylinositol implicated in insulin action by a combination of two complementary methods: (a) chemical labelling with a non-permeable (isethionyl acetimidate) and a permeable (ethyl acetimidate) probe; and (b) enzymatic modifications with beta-galactosidase (EC 3.2.1.23) or phosphatidylinositol-specific phospholipase C (EC 3.1.4.3). Using the first approach the majority of the glycosyl-phosphatidylinositol is found in the outer surface of intact hepatocytes, adipocytes, fibroblasts and lymphocytes, but not in erythrocytes which presented only a 20% of the total labelled glycosyl-phosphatidylinositol to the exterior. Upon insulin addition (10 nM), about 60% of the total glycosyl-phosphatidylinositol was hydrolysed in both hepatocytes and adipocytes but not in erythrocytes. In agreement with the extracellular localization in hepatocytes and with the proposed role of this glycolipid in insulin action, treatment of rat hepatocytes with beta-galactosidase from Escherichia coli, an enzyme that hydrolyses the oligosaccharide moiety of the glycosyl-phosphatidylinositol, cleaved 65% of the total glycophospholipid and blocked the effect of insulin (but not of glucagon) on pyruvate kinase (EC 2.7.1.40). Similar treatment with phosphatidylinositol-specific phospholipase C from Bacillus cereus hydrolysed 62% of the total glycosyl-phosphatidylinositol. From the various approaches used it is concluded that the majority of this glycophospholipid is at the outer surface in a variety of insulin-sensitive cells.

Cross-linking of phosphatidylethanolamine neighbors with dimethylsuberimidate is sensitive to the lipid phase

Dimethylsuberimidate was reacted with aqueous dispersions of dipalmitoylphosphatidylethanolamine, dimyristoylphosphatidylethanolamine, dilauroylphosphatidylethanolamine, and dielaidoylphosphatidylethanolamine at pH 10 and at pH 8. The amount of amidine dimer formation was about four times greater above the gel-to-fluid phase transition of each lipid than below the transition. The transition temperature of each phosphatidylethanolamine, measured by steady-state fluorescence anisotropy of cis-parinaric acid, was lower at pH 10 than at pH 8 or in water. The ability of dimethylsuberimidate to discriminate between phosphatidylethanolamines in the fluid and gel phases should allow use of this reagent to identify phosphatidylethanolamine species within the gel or fluid lipid phase.

Isolation and characterization of functional Shiga toxin subunits and renatured holotoxin

Shiga toxin is a protein toxin produced by Shigella dysenteriae type I strains. In this report we present a procedure for the separation of functionally intact toxin A and B chains and for their reconstitution to form biologically active molecules. In agreement with the findings of others, the isolated A chain was shown to be a potent in vitro inhibitor of eukaryotic protein synthesis. The isolated B chain bound to HeLa cells and competitively inhibited the binding and cytotoxic activity of holotoxin. These findings show that the functional role of the B chain is to recognize cell surface functional receptors. By labelling the B subunit alone, prior to renaturation of holotoxin, the polypeptide chains were shown to associate noncovalently with a stoichiometry of one A chain and five B chains.

Analysis of dimeric species derived from the reaction of phosphatidylethanolamine with dimethylsuberimidate

Phosphatidylethanolamines of various fatty acyl species in vortexed lipid dispersions were reacted with dimethylsuberimidate to produce dimeric products. The yield was 34% at pH 10 and 2% at pH 7. The crosslinked phosphatidylethanolamine species were separated from minor products and the reactants by extraction and two-dimensional thin-layer chromatography on silica gel G, gel filtration on lipophilic Sephadex, or C18-reversed phase high-performance liquid chromatography (HPLC). Reversed phase HPLC was also used to resolve the dimers into individual molecular species. Analysis of the dimers revealed the extinction coefficients at 205 nm to be higher than those of the reactant phosphatidylethanolamines. Proton nuclear magnetic resonance spectroscopy and chemical analysis implied that the dimers contain an amidine group.

Identification of neighboring protein pairs in the 60 S ribosomal subunits from Saccharomyces cerevisiae by chemical cross-linking

Protein-protein cross-linking was used to determine the spatial arrangement of proteins within the 60 S ribosomal subunits of Saccharomyces cerevisiae. Protein cross-links were generated by treatment of intact ribosomal subunits with dimethyl 3,3'-dithiobispropionimidate. Proteins were extracted from the treated subunits and fractionated by Cm-cellulose chromatography. Cross-linked proteins in these fractions were analyzed by electrophoresis on two-dimensional diagonal polyacrylamide gels containing sodium dodecyl sulfate. Component members of cross-linked pairs were radiolabeled with 125I and identified by two-dimensional gel electrophoresis and comparison with nonradioactive ribosomal protein markers. Seventeen pairs involving 16 of the 45 60 S subunit proteins were identified. Several proteins were detected in numerous cross-linked dimers and were used as foci for constructing a model depicting the arrangement of proteins within the 60 S ribosomal subunit. The model also incorporated previously published data on structure and function of proteins from the yeast 60 S subunit.

Preparation and properties of a holo-lactate dehydrogenase enzyme reactor

NAD+ was the base material for syntheses of coenzyme analogs with reactive groups bound to N6 of the adenine moiety via spacers that are 3-17 A long. These analogs were used for the modification of dehydrogenases. Aromatic imidoesters and acyl azides are suitable reactive groups, which form covalent amidinium or amide bonds with amino acid residues such as the epsilon-amino groups of lysines. The catalytic function of the modified protein decreased only slightly. Coenzymes that are linked via a spacer to carboxyl and amino groups are fixed to the protein by means of carbodiimides and hydroxysuccinimide. Coenzyme-bound aromatic imidoesters with spacer lengths of more than 12 A were incorporated to the extent of 60% at the active site. Aliphatic imidoesters proved to be inefficient for protein modification because of fast hydrolysis. Fixing of coenzyme analogs containing appended carboxyl or amino groups to enzyme in the presence of carbodiimides resulted in a decrease of enzyme activity. Modified lactate dehydrogenase and L-alanine dehydrogenase formed an enzyme reactor for the production of L-alanine in the absence of free NAD+. Both enzymes were cross-linked by dimethyl suberimidate in the presence or absence of NAD+, bis-NAD+, pyruvate, and oxamate. Site-to-site directed cross-linking yielded a reaction mixture from which four protein fractions were obtained by isoelectric focusing; one of these showed a cycling rate of 600 h-1.

[The reaction of imidates with isocyanates]

Derivatives of isocyanates were prepared by reaction with imidates. Fragmentation reactions and behaviour in a simple biological test were examined.

Immunoblotting analysis of protein-protein crosslinks within the 50S ribosomal subunit of Escherichia coli. A study using dimethylsuberimidate as crosslinking reagent

50S ribosomal subunits of Escherichia coli have been crosslinked with the bifunctional imidoester dimethyl-suberimidate and the protein-protein crosslinks have been analyzed by immunoblotting, using antisera specific for the individual ribosomal proteins of the large ribosomal subunit. Crosslinked protein pairs which occurred in yields higher than 5% have been unambiguously identified. Thus 13 crosslinks have been identified, namely L1-L33, L5-L7/12, L6-L19, L7/12-L10, L7/12-L11, L9-L28, L10-L11, L13-L20, L16-L27, L17-L32, L18-L22, L19-L25 and L27-L33. These data, together with the results which we will be presenting elsewhere, contribute considerably to our knowledge of the protein topography of the 50S ribosomal proteins as determined by immunoelectron microscopy. We can now propose the approximate locations of ten proteins that have not previously been localized.

[Synthesis of a tetrasaccharide unit of the capsular polysaccharide of Streptococcus pneumoniae type 9V]

In the synthesis of 8-methoxycarbonyloctyl O-(alpha-D-galactopyranosyl)-(1----3)-O-(2-acetamido-2-deoxy-beta-D- mannopyranosyl)-(1----4)-O-(beta-D-glucopyranosyl)-(1----4)-alpha-D- glucopyranoside, which represents a component of the capsular polysaccharide of Streptococcus pneumoniae type 9V, the key step was the coupling of alpha-D-Galp-(1----3)-beta-D-ManpNAc-(1----4)-D-Glc as glycosyl donor with 8-ethoxy-carbonyloctyl 6-O-acetyl-2,3-di-O-benzyl-alpha-D-glucopyranoside as glycosyl acceptor by use of the imidate method. Only the beta-imidate of the trisaccharide could be employed in this glycosidation reaction to give stereoselectively the tetrasaccharide in high yield. The alpha-imidate of the trisaccharide led to hydrolysis of the imidate group.

Protein-protein cross-linking of the 50 S ribosomal subunit of Escherichia coli using 2-iminothiolane. Identification of cross-links by immunoblotting techniques

We have investigated the protein-protein cross-links formed within the 50 S subunit of the Escherichia coli ribosome using 2-iminothiolane as the cross-linking reagent. The members of the cross-links have been identified by immunoblotting from one-dimensional and two-dimensional diagonal sodium dodecyl sulfate-polyacrylamide gels using antisera specific for the individual ribosomal proteins. This method also allowed a quantitation of the yield of cross-linking for each cross-link. A total of 14 cross-links have been identified: L1-L33, L2-L9, L2-L9-L28, L3-L19, L9-L28, L13-L21, L14-L19, L16-L27, L17-L30, L17-L32, L19-L25, L20-L21, L22-L32, and L23-L34. Our results are compared with those of Traut and coworkers (Traut, R. R., Tewari, D. S., Sommer, A., Gavino, G. R., Olson, H. M., and Glitz, D. G. (1986) in Structure, Function and Genetics of Ribosomes (Hardesty, B. and Kramer, G., eds) pp. 286-308, Springer-Verlag, New York). Our cross-linking data allow us to propose the approximate locations of eight proteins of the 50 S ribosomal subunit that so far have not been localized by immunoelectron microscopy and they thus contribute considerably to our knowledge of ribosome structure.

Detection of a Myc-associated protein by chemical cross-linking

A single nuclear protein (Myc-associated protein) can be specifically cross-linked to avian Myc proteins by treatment of nuclei or cells with the reversible cross-linker dimethyl 3,3'-dithiobis-propionimidate. Myc-associated protein has a molecular weight of approximately 500,000, is not detectably phosphorylated and, in contrast to Myc, has a long apparent half-life of greater than 3 h.

Cross-linking of the electron-transfer flavoprotein to electron-transfer flavoprotein-ubiquinone oxidoreductase with heterobifunctional reagents

The mitochondrial electron-transfer flavoprotein (ETF) is a heterodimer containing only one FAD. In previous work on the structure-function relationships of ETF, its interaction with the general acyl-CoA dehydrogenase (GAD) was studied by chemical cross-linking with heterobifunctional reagents [D. J. Steenkamp (1987) Biochem. J. 243, 519-524]. GAD whose lysine residues were substituted with 3-(2-pyridyldithio)propionyl groups was preferentially cross-linked to the small subunit of ETF, the lysine residues of which had been substituted with 4-mercaptobutyramidine (MBA) groups. This work was extended to the interaction of ETF with ETF-ubiquinone oxidoreductase (ETF-Q ox). ETF-Q ox was partially inactivated by modification with N-succinimidyl 3-(2-pyridyldithio)propionate to introduce pyridyl disulphide structures. A similar modification of ETF caused a large increase in the apparent Michaelis constant of ETF-Q ox for modified ETF owing to the loss of positive charge on some critical lysines of ETF. When ETF-Q ox was modified with 2-iminothiolane to introduce 4-mercaptobutyramidine groups, only a minor effect on the activity of the enzyme was observed. To retain the positive charges on the lysine residues of ETF, pyridyl disulphide structures were introduced by treating ETF with 2-iminothiolane in the presence of 2,2'-dithiodipyridyl. The electron-transfer activity of the resultant ETF preparation containing 4-(2-pyridyldithio)butyramidine (PDBA) groups was only slightly affected. When ETF-Q ox substituted with MBA groups was mixed with ETF bearing PDBA groups, at least 70% of the cross-links formed between the two proteins were between the small subunit of ETF and ETF-Q ox. ETF-Q ox, therefore, interacts predominantly with the same subunit of ETF as GAD. Variables which affect the selectivity of ETF-Q ox cross-linking to the subunits of ETF are considered.

Evidence for the extramembranous location of the putative amphipathic helix of acetylcholine receptor

Evidence has been obtained demonstrating that the peptides GVKYIAE and AIKYIAE found in the potential amphipathic helices of the alpha and beta subunits, respectively, of acetylcholine receptor are not buried in the membrane. The peptide KYIAE was synthesized, and polyclonal antibodies were prepared against a conjugate of bovine serum albumin and synthetic peptide. An immunoadsorbent capable of binding and subsequently releasing peptides ending with the sequence-YIAE was produced by attaching these specific antibodies to agarose. Native acetylcholine receptor was labeled with pyridoxal phosphate and Na[3H]BH4. The labeled protein was stripped of phospholipid and digested with the protease from Staphylococcus aureus strain V8. The digest was submitted to immunoadsorption to isolate the labeled indigenous peptides. As a control, alpha and beta polypeptides prepared by gel filtration of a solution of acetylcholine receptor in detergent were stripped of detergent and labeled with pyridoxal phosphate and Na[3H]BH4 in the presence of 8 M urea. The labeled alpha and beta polypeptides were digested and submitted to immunoadsorption. The specific radioactivities of the indigenous peptides from the alpha and beta subunits labeled under native and denaturing conditions were nearly equal. In similar experiments using isethionyl (2', 4'-dinitrophenyl)-3-amino-propionimidate as the labeling agent, the indigenous peptides from native and denatured receptor were also labeled to the same extent. Since these peptides are labeled to the same extent whether or not the protein is denatured, they cannot be buried in the membrane.