Synthesis of α-hydroxy ketones and vicinal diols with the Bacillus licheniformis DSM 13T butane-2,3-diol dehydrogenase

The enantioselective synthesis of α-hydroxy ketones and vicinal diols is an intriguing field because of the broad applicability of these molecules. Although, butandiol dehydrogenases are known to play a key role in the production of 2,3-butandiol, their potential as biocatalysts is still not well studied. Here, we investigate the biocatalytic properties of the meso-butanediol dehydrogenase from Bacillus licheniformis DSM 13^T (BlBDH). The encoding gene was cloned with an N-terminal StrepII-tag and recombinantly overexpressed in E. coli. BlBDH is highly active towards several non-physiological diketones and α-hydroxyketones with varying aliphatic chain lengths or even containing phenyl moieties. By adjusting the reaction parameters in biotransformations the formation of either the α-hydroxyketone intermediate or the diol can be controlled.

Synthesis of α-hydroxy ketones and vicinal (R,R)-diols by Bacillus clausii DSM 8716T butanediol dehydrogenase

α-hydroxy ketones (HK) and 1,2-diols are important building blocks for fine chemical synthesis. Here, we describe the R-selective 2,3-butanediol dehydrogenase from B. clausii DSM 8716^T (BcBDH) that belongs to the metal-dependent medium chain dehydrogenases/reductases family (MDR) and catalyzes the selective asymmetric reduction of prochiral 1,2-diketones to the corresponding HK and, in some cases, the reduction of the same to the corresponding 1,2-diols. Aliphatic diketones, like 2,3-pentanedione, 2,3-hexanedione, 5-methyl-2,3-hexanedione, 3,4-hexanedione and 2,3-heptanedione are well transformed. In addition, surprisingly alkyl phenyl dicarbonyls, like 2-hydroxy-1-phenylpropan-1-one and phenylglyoxal are accepted, whereas their derivatives with two phenyl groups are not substrates. Supplementation of Mn²⁺ (1 mM) increases BcBDH's activity in biotransformations. Furthermore, the biocatalytic reduction of 5-methyl-2,3-hexanedione to mainly 5-methyl-3-hydroxy-2-hexanone with only small amounts of 5-methyl-2-hydroxy-3-hexanone within an enzyme membrane reactor is demonstrated.

Reduction of symmetric or asymmetric vicinal diketones with BcBDH leads to the synthesis of either α-hydroxyketones or vicinal diols.

Screen-Printed Carbon Electrodes Modified with Graphene Oxide for the Design of a Reagent-Free NAD+-Dependent Biosensor Array

A facile approach for the construction of reagent-free electrochemical dehydrogenase-based biosensors is presented. Enzymes and cofactors (NAD⁺ and Fe(CN)₆^3-) were immobilized by modification of screen-printed carbon electrodes with graphene oxide (GO) and an additional layer of cellulose acetate. The sensor system was exemplarily optimized for an l-lactate electrode in terms of GO concentration, working potential, and pH value. The biosensor exhibited best characteristics at pH 7.5 in 100 mM potassium phosphate buffer at an applied potential of +0.250 V versus an internal pseudo Ag reference electrode. Thereby, sensor performance was characterized by a linear working range from 0.25 to 4 mM and a sensitivity of 0.14 μA mM^-1. The detection principle was additionally evaluated with three other dehydrogenases (d-lactate dehydrogenase, alcohol dehydrogenase, and formate dehydrogenase, respectively). The developed reagentless biosensor array enabled simultaneous and cross-talk free determination of l-lactate, d-lactate, ethanol, and formate.

Quantitative differential monitoring of the metabolic activity of Corynebacterium glutamicum cultures utilizing a light-addressable potentiometric sensor system

Applying biosensors for evaluation of the extracellular acidification of microorganisms in various biotechnological fermentation processes is on demand. An early stage detection of disturbances in the production line would avoid costly interventions related to metabolically inactive microorganisms. Furthermore, the determination of the number of living cells through cell plating procedure after cultivations is known as time- and material-consuming. In this work, a differential light-addressable potentiometric sensor (LAPS) system was developed to monitor the metabolic activity of Corynebacterium glutamicum (C. glutamicum ATCC13032) as typical microorganism in fermentation processes. In this context, the number of living cells in suspensions was directly determined utilizing the read-out principle of the LAPS system. The planar sensor surface of the LAPS design allows to fixate 3D-printed multi-chamber structures, which enables differential measurements. In this way, undesirable external influences such as pH variations of the medium and sensor signal drift can be compensated.

Toward a Hybrid Biosensor System for Analysis of Organic and Volatile Fatty Acids in Fermentation Processes

Monitoring of organic acids (OA) and volatile fatty acids (VFA) is crucial for the control of anaerobic digestion. In case of unstable process conditions, an accumulation of these intermediates occurs. In the present work, two different enzyme-based biosensor arrays are combined and presented for facile electrochemical determination of several process-relevant analytes. Each biosensor utilizes a platinum sensor chip (14 × 14 mm2) with five individual working electrodes. The OA biosensor enables simultaneous measurement of ethanol, formate, d- and l-lactate, based on a bi-enzymatic detection principle. The second VFA biosensor provides an amperometric platform for quantification of acetate and propionate, mediated by oxidation of hydrogen peroxide. The cross-sensitivity of both biosensors toward potential interferents, typically present in fermentation samples, was investigated. The potential for practical application in complex media was successfully demonstrated in spiked sludge samples collected from three different biogas plants. Thereby, the results obtained by both of the biosensors were in good agreement to the applied reference measurements by photometry and gas chromatography, respectively. The proposed hybrid biosensor system was also used for long-term monitoring of a lab-scale biogas reactor (0.01 m3) for a period of 2 months. In combination with typically monitored parameters, such as gas quality, pH and FOS/TAC (volatile organic acids/total anorganic carbonate), the amperometric measurements of OA and VFA concentration could enhance the understanding of ongoing fermentation processes.

Development and characterization of a field-effect biosensor for the detection of acetoin

A capacitive electrolyte-insulator-semiconductor (EIS) field-effect biosensor for acetoin detection has been presented for the first time. The EIS sensor consists of a layer structure of Al/p-Si/SiO₂/Ta₂O₅/enzyme acetoin reductase. The enzyme, also referred to as butane-2,3-diol dehydrogenase from B. clausii DSM 8716^T, has been recently characterized. The enzyme catalyzes the (R)-specific reduction of racemic acetoin to (R,R)- and meso-butane-2,3-diol, respectively. Two different enzyme immobilization strategies (cross-linking by using glutaraldehyde and adsorption) have been studied. Typical biosensor parameters such as optimal pH working range, sensitivity, hysteresis, linear concentration range and long-term stability have been examined by means of constant-capacitance (ConCap) mode measurements. Furthermore, preliminary experiments have been successfully carried out for the detection of acetoin in diluted white wine samples.

Application of a Portable Multi-Analyte Biosensor for Organic Acid Determination in Silage

Multi-analyte biosensors may offer the opportunity to perform cost-effective and rapid analysis with reduced sample volume, as compared to electrochemical biosensing of each analyte individually. This work describes the development of an enzyme-based biosensor system for multi-parametric determination of four different organic acids. The biosensor array comprises five working electrodes for simultaneous sensing of ethanol, formate, d-lactate, and l-lactate, and an integrated counter electrode. Storage stability of the biosensor was evaluated under different conditions (stored at +4 °C in buffer solution and dry at −21 °C, +4 °C, and room temperature) over a period of 140 days. After repeated and regular application, the individual sensing electrodes exhibited the best stability when stored at −21 °C. Furthermore, measurements in silage samples (maize and sugarcane silage) were conducted with the portable biosensor system. Comparison with a conventional photometric technique demonstrated successful employment for rapid monitoring of complex media.

Development of a plasmid-based, tunable, tolC-derived expression system for application in Cupriavidus necator H16

Cupriavidus necator H16 gains increasing attention in microbial research and biotechnological application due to its diverse metabolic features. Here we present a tightly controlled gene expression system for C. necator including the pBBR1-vector that contains hybrid promoters originating from C. necator native tolC-promoter in combination with a synthetic tetO-operator. The expression of the reporter gene from these plasmids relies on the addition of the exogenous inducer doxycycline (dc). The novel expression system offers a combination of advantageous features as; (i) high and dose-dependent recombinant protein production, (ii) tight control with a high dynamic range (On/Off ratio), which makes it applicable for harmful pathways or for toxic protein production, (iii) comparable cheap inducer (doxycycline, dc), (iv) effective at low inducer concentration, that makes it useful for large scale application, (v) rapid, diffusion controlled induction, and (vi) the inducer does not interfere within the cell metabolism. As applications of the expression system in C. necator H16, the growth ability on glycerol was enhanced by constitutively expressing the E. coli glpk gene-encoding for glycerol kinase. Likewise, we used the system to overcome the expression toxicity of mevalonate pathway in C. necator H16. With this system, the mevalonate-genes were successfully introduced in the host and the recombinant strains could produce about 200 mg/l mevalonate.

The semiquinone swing in the bifurcating electron transferring flavoprotein/butyryl-CoA dehydrogenase complex from Clostridium difficile

The electron transferring flavoprotein/butyryl-CoA dehydrogenase (EtfAB/Bcd) catalyzes the reduction of one crotonyl-CoA and two ferredoxins by two NADH within a flavin-based electron-bifurcating process. Here we report on the X-ray structure of the Clostridium difficile (EtfAB/Bcd)₄ complex in the dehydrogenase-conducting D-state, α-FAD (bound to domain II of EtfA) and δ-FAD (bound to Bcd) being 8 Å apart. Superimposing Acidaminococcus fermentans EtfAB onto C. difficile EtfAB/Bcd reveals a rotation of domain II of nearly 80°. Further rotation by 10° brings EtfAB into the bifurcating B-state, α-FAD and β-FAD (bound to EtfB) being 14 Å apart. This dual binding mode of domain II, substantiated by mutational studies, resembles findings in non-bifurcating EtfAB/acyl-CoA dehydrogenase complexes. In our proposed mechanism, NADH reduces β-FAD, which bifurcates. One electron goes to ferredoxin and one to α-FAD, which swings over to reduce δ-FAD to the semiquinone. Repetition affords a second reduced ferredoxin and δ-FADH⁻, which reduces crotonyl-CoA.

The electron-transferring flavoprotein / butyryl-CoA dehydrogenase (EtfAB/Bcd) complex catalyzes the reduction of crotonyl-CoA and ferredoxins by NADH in anaerobic microbes. Here, the authors present the crystal structure of Clostridium difficile EtfAB/Bcd and discuss the bifurcation mechanism for electron flow.

(R,R)-Butane-2,3-diol dehydrogenase from Bacillus clausii DSM 8716T: Cloning and expression of the bdhA-gene, and initial characterization of enzyme

The gene encoding a putative (R,R)-butane-2,3-diol dehydrogenase (bdhA) from Bacillus clausii DSM 8716^T was isolated, sequenced and expressed in Escherichia coli. The amino acid sequence of the encoded protein is only distantly related to previously studied enzymes (identity 33-43%) and exhibited some uncharted peculiarities. An N-terminally StrepII-tagged enzyme variant was purified and initially characterized. The isolated enzyme catalyzed the (R)-specific oxidation of (R,R)- and meso-butane-2,3-diol to (R)- and (S)-acetoin with specific activities of 12U/mg and 23U/mg, respectively. Likewise, racemic acetoin was reduced with a specific activity of up to 115U/mg yielding a mixture of (R,R)- and meso-butane-2,3-diol, while the enzyme reduced butane-2,3-dione (V_max 74U/mg) solely to (R,R)-butane-2,3-diol via (R)-acetoin. For these reactions only activity with the co-substrates NADH/NAD⁺ was observed. The enzyme accepted a selection of vicinal diketones, α-hydroxy ketones and vicinal diols as alternative substrates. Although the physiological function of the enzyme in B. clausii remains elusive, the data presented herein clearly demonstrates that the encoded enzyme is a genuine (R,R)-butane-2,3-diol dehydrogenase with potential for applications in biocatalysis and sensor development.

A flexible toolbox to study protein-assisted metalloenzyme assembly in vitro

A number of metalloenzymes harbor unique cofactors, which are incorporated into the apo-enzymes via protein-assisted maturation. In the case of [NiFe]-hydrogenases, minimally seven maturation factors (HypABCDEF and a specific endopeptidase) are involved, making these enzymes an excellent example for studying metallocenter assembly in general. Here, we describe an innovative toolbox to study maturation involving multiple putative gene products. The two core elements of the system are a modular, combinatorial cloning system and a cell-free maturation system, which is based on recombinant Escherichia coli extracts and/or purified maturases. Taking maturation of the soluble, oxygen-tolerant [NiFe]-hydrogenase (SH) from Cupriavidus necator as an example, the capacities of the toolbox are illustrated. In total 18 genes from C. necator were analyzed, including four SH-structural genes, the SH-dedicated hyp-genes and a second set of hyp-genes putatively involved in maturation of the Actinobacterium-like hydrogenase (AH). The two hyp-sets were either expressed in their entirety from single vectors or split into functional modules, which enabled flexible approaches to investigate limitations, specificities and the capabilities of individual constituents to functionally substitute each other. Affinity-tagged Hyp-Proteins were used in pull-down experiments to demonstrate direct interactions between dedicated or non-related constituents. The dedicated Hyp-set from C. necator exhibited the highest maturation efficiency in vitro. Constituents of non-related maturation machineries were found to interact with and to accomplish partial activation of SH. In contrast to homologues of the Hyp-family, omission of the SH-specific endopeptidase HoxW completely abolished in vitro maturation. We detected stoichiometric imbalances inside the recombinant production system, which point to limitations by the cyanylation complex HypEF and the premature subunit HoxH. Purification of HoxW revealed strong indications for the presence of a putative [4Fe-4S]-cluster, which is unique among this class of maturases. Results are discussed in the context of [NiFe]-hydrogenase maturation, and in light of the capacity of the novel toolbox.

High resolution crystal structure of Clostridium propionicum β-alanyl-CoA:ammonia lyase, a new member of the "hot dog fold" protein superfamily

Clostridium propionicum is the only organism known to ferment β-alanine, a constituent of coenzyme A (CoA) and the phosphopantetheinyl prosthetic group of holo-acyl carrier protein. The first step in the fermentation is a CoA-transfer to β-alanine. Subsequently, the resulting β-alanyl-CoA is deaminated by the enzyme β-alanyl-CoA:ammonia lyase (Acl) to reversibly form ammonia and acrylyl-CoA. We have determined the crystal structure of Acl in its apo-form at a resolution of 0.97 Å as well as in complex with CoA at a resolution of 1.59 Å. The structures reveal that the enyzme belongs to a superfamily of proteins exhibiting a so called "hot dog fold" which is characterized by a five-stranded antiparallel β-sheet with a long α-helix packed against it. The functional unit of all "hot dog fold" proteins is a homodimer containing two equivalent substrate binding sites which are established by the dimer interface. In the case of Acl, three functional dimers combine to a homohexamer strongly resembling the homohexamer formed by YciA-like acyl-CoA thioesterases. Here, we propose an enzymatic mechanism based on the crystal structure of the Acl·CoA complex and molecular docking.

An innovative cloning platform enables large-scale production and maturation of an oxygen-tolerant [NiFe]-hydrogenase from Cupriavidus necator in Escherichia coli

Expression of multiple heterologous genes in a dedicated host is a prerequisite for approaches in synthetic biology, spanning from the production of recombinant multiprotein complexes to the transfer of tailor-made metabolic pathways. Such attempts are often exacerbated, due in most cases to a lack of proper directional, robust and readily accessible genetic tools. Here, we introduce an innovative system for cloning and expression of multiple genes in Escherichia coli BL21 (DE3). Using the novel methodology, genes are equipped with individual promoters and terminators and subsequently assembled. The resulting multiple gene cassettes may either be placed in one vector or alternatively distributed among a set of compatible plasmids. We demonstrate the effectiveness of the developed tool by production and maturation of the NAD(+)reducing soluble [NiFe]-hydrogenase (SH) from Cupriavidus necator H16 (formerly Ralstonia eutropha H16) in E. coli BL21Star™ (DE3). The SH (encoded in hoxFUYHI) was successfully matured by co-expression of a dedicated set of auxiliary genes, comprising seven hyp genes (hypC1D1E1A2B2F2X) along with hoxW, which encodes a specific endopeptidase. Deletion of genes involved in SH maturation reduced maturation efficiency substantially. Further addition of hoxN1, encoding a high-affinity nickel permease from C. necator, considerably increased maturation efficiency in E. coli. Carefully balanced growth conditions enabled hydrogenase production at high cell-densities, scoring mg·(Liter culture)(-1) yields of purified functional SH. Specific activities of up to 7.2±1.15 U·mg(-1) were obtained in cell-free extracts, which is in the range of the highest activities ever determined in C. necator extracts. The recombinant enzyme was isolated in equal purity and stability as previously achieved with the native form, yielding ultrapure preparations with anaerobic specific activities of up to 230 U·mg(-1). Owing to the combinatorial power exhibited by the presented cloning platform, the system might represent an important step towards new routes in synthetic biology.

Facile analysis of short-chain fatty acids as 4-nitrophenyl esters in complex anaerobic fermentation samples by high performance liquid chromatography

Short-chain fatty acids are crucial intermediates in the conversion of biomass to methane. Due to the complexity of raw biomass, volatile fatty acids (including n- and branched-chain compounds) as well as arylacetic and arylpropionic acids arise from digestion of carbohydrates, proteins and lipids. The development of a simple extraction procedure in combination with internal standardization and facile 4-nitrophenyl-labelling via oxalylchloride-generated acylchlorides enabled robust separation and quantification of the target compounds in crude biological samples like raw cattle manure and biogas fermenter contents. Detection limits of <100 μM and error rates of less than 4% for the quantification of individual compounds in a concentration range up to 50 mM for non-diluted samples suggest that the novel method might be of general advantage for the routine quantification of short-chain fatty acids in complex biological samples including complex fermentation media.

Comparison of intravenous immunoglobulins for naturally occurring autoantibodies against amyloid-beta

Intravenous immunoglobulins (IVIG) are currently used for therapeutic purposes in autoimmune disorders. Recently, we demonstrated the presence of naturally occurring antibodies against amyloid-beta (nAbs-Abeta) within the pool of IVIG. In this study, we compared different brands of IVIG for nAbs-Abeta and have found differences in the specificity of the nAbs-Abeta towards Abeta(1-40) and Abeta(1-42). We analyzed the influence of a pH-shift over the course of antibody storage using ELISA and investigated antibody dimerization at acidic and neutral pH as well as differences in the IgG subclass distributions among the IVIG using both HPLC and a nephelometric assay. Furthermore, we investigated the epitope region of purified nAbs-Abeta. The differences found in Abeta specificity are not directly proportionate to the binding nature of these antibodies when administered in vivo. This information, however, may serve as a guide when choosing the commercial source of IVIG for therapeutic applications in Alzheimer's disease.

Characterization of (R)-2-hydroxyisocaproate dehydrogenase and a family III coenzyme A transferase involved in reduction of L-leucine to isocaproate by Clostridium difficile

The strictly anaerobic pathogenic bacterium Clostridium difficile occurs in the human gut and is able to thrive from fermentation of leucine. Thereby the amino acid is both oxidized to isovalerate plus CO(2) and reduced to isocaproate. In the reductive branch of this pathway, the dehydration of (R)-2-hydroxyisocaproyl-coenzyme A (CoA) to (E)-2-isocaprenoyl-CoA is probably catalyzed via radical intermediates. The dehydratase requires activation by an ATP-dependent one-electron transfer (J. Kim, D. Darley, and W. Buckel, FEBS J. 272:550-561, 2005). Prior to the dehydration, a dehydrogenase and a CoA transferase are supposed to be involved in the formation of (R)-2-hydroxyisocaproyl-CoA. Deduced amino acid sequences of ldhA and hadA from the genome of C. difficile showed high identities to d-lactate dehydrogenase and family III CoA transferase, respectively. Both putative genes encoding the dehydrogenase and CoA transferase were cloned and overexpressed in Escherichia coli; the recombinant Strep tag II fusion proteins were purified to homogeneity and characterized. The substrate specificity of the monomeric LdhA (36.5 kDa) indicated that 2-oxoisocaproate (K(m) = 68 muM, k(cat) = 31 s(-1)) and NADH were the native substrates. For the reverse reaction, the enzyme accepted (R)- but not (S)-2-hydroxyisocaproate and therefore was named (R)-2-hydroxyisocaproate dehydrogenase. HadA showed CoA transferase activity with (R)-2-hydroxyisocaproyl-CoA as a donor and isocaproate or (E)-2-isocaprenoate as an acceptor. By site-directed mutagenesis, the conserved D171 was identified as an essential catalytic residue probably involved in the formation of a mixed anhydride with the acyl group of the thioester substrate. However, neither hydroxylamine nor sodium borohydride, both of which are inactivators of the CoA transferase, modified this residue. The dehydrogenase and the CoA transferase fit well into the proposed pathway of leucine reduction to isocaproate.

4-Hydroxyphenylacetate Decarboxylases: Properties of a Novel Subclass of Glycyl Radical Enzyme Systems†

The 4-hydroxyphenylacetate decarboxylases from Clostridium difficile and Clostridium scatologenes, which catalyze the formation of p-cresol, form a distinct group of glycyl radical enzymes (GREs). Cresol formation provides metabolic toxicity, which allows an active suppression of other microbes and may provide growth advantages for the producers in highly competitive environments. The GRE decarboxylases are characterized by a small subunit, which is not similar to any protein of known function in the databases, and provides unique properties that have not been observed in other GREs. Both decarboxylases are functional hetero-octamers (beta(4)gamma(4)), which contain iron-sulfur centers in addition to the glycyl radical prosthetic group. The small subunit is responsible for metal binding and is also involved in the regulation of the enzymes' oligomeric state and activity, which are triggered by reversible serine phosphorylation of the glycyl radical subunits. Biochemical data suggest that the iron-sulfur centers of the decarboxylases could be involved in the radical dissipation of previously activated enzymes in the absence of substrate. The cognate activating enzymes differ from their Pfl and Nrd counterparts in that up to two iron-sulfur centers, in addition to the characteristic SAM cluster, were found. Biochemical data suggested that these [4Fe-4S] centers are involved in the electron transfer to the SAM cluster but do not directly participate in the reductive cleavage of SAM. These data imply a tight regulation of p-cresol formation, which is necessary in order to avoid detrimental effects of the toxic product on the producers.

New glycyl radical enzymes catalysing key metabolic steps in anaerobic bacteria

During the last decade, an increasing number of new enzymes containing glycyl radicals in their active sites have been identified and biochemically characterised. These include benzylsuccinate synthase (Bss), 4-hydroxyphenylacetate decarboxylase (Hpd) and the coenzyme B12-independent glycerol dehydratase (Gdh). These are involved in metabolic pathways as different as anaerobic toluene metabolism, fermentative production of p-cresol and glycerol fermentation. Some features of these newly discovered enzymes are described and compared with those of the previously known glycyl radical enzymes pyruvate formate-lyase (Pfl) and anaerobic ribonucleotide reductase (Nrd). Among the new enzymes, Bss and Hpd share the presence of small subunits, the function of which in the catalytic mechanisms is still enigmatic, and both enzymes contain metal centres in addition to the glycyl radical prosthetic group. The activating enzymes of the novel systems also deviate from the standard type, containing at least one additional Fe-S cluster. Finally, the available whole-genome sequences of an increasing number of strictly or facultative anaerobic bacteria revealed the presence of many more hitherto unknown glycyl radical enzyme (GRE) systems. Recent studies suggest that the particular types of these enzymes represent the ends of different evolutionary lines, which emerged early in evolution and diversified to yield remarkably versatile biocatalysts for chemical reactions that are otherwise difficult to perform in anoxic environments.

Properties and significance of apoFNR as a second form of air-inactivated [4Fe-4S]·FNR of Escherichia coli

The active form of the oxygen sensor fumarate nitrate reductase regulator (FNR) of Escherichia coli contains a [4Fe-4S] cluster which is converted to a [2Fe-2S] cluster after reaction with air, resulting in inactivation of FNR. Reaction of reconstituted [4Fe-4S].FNR with air resulted within 5 min in conversion to apoFNR. The rate was comparable to the rate known for [4Fe-4S].FNR/[2Fe-2S].FNR cluster conversion, suggesting that apoFNR is a product of [2Fe-2S].FNR decomposition and a final form of air-inactivated FNR in vitro. Formation of apoFNR and the redox state of the cysteinyl residues were determined in vitro by alkylation. FNR contains five cysteinyl residues, four of which (Cys20, Cys23, Cys29 and Cys122) ligate the FeS clusters. Alkylated FNR and proteolytic fragments thereof were analyzed by MALDI-TOF. ApoFNR formed by air inactivation of [4Fe-4S].FNR in vitro contained one or two disulfides. Only disulfide pairs Cys16/20 and Cys23/29 were formed; Cys122 was never part of a disulfide. The same type of disulfide was found in apoFNR obtained during isolation of FNR, suggesting that cysteine disulfide formation follows a fixed pattern. ApoFNR, including the form with two disulfides, can be reconstituted to [4Fe-4S].FNR after disulfide reduction. The experiments suggest that apoFNR is a major form of FNR under oxic conditions.

Two beta-alanyl-CoA:ammonia lyases in Clostridium propionicum

The fermentation of beta-alanine by Clostridium propionicum proceeds via activation to the CoA-thiol ester, followed by deamination to acryloyl-CoA, which is also an intermediate in the fermentation of l-alanine. By shifting the organism from the carbon and energy source alpha-alanine to beta-alanine, the enzyme beta-alanyl-CoA:ammonia lyase is induced 300-fold (approximately 30% of the soluble protein). The low basal lyase activity is encoded by the acl1 gene, whereas the almost identical acl2 gene (six amino acid substitutions) is responsible for the high activity after growth on beta-alanine. The deduced beta-alanyl-CoA:ammonia lyase proteins are related to putative beta-aminobutyryl-CoA ammonia lyases involved in lysine fermentation and found in the genomes of several anaerobic bacteria. beta-Alanyl-CoA:ammonia lyase 2 was purified to homogeneity and characterized as a heteropentamer composed of 16 kDa subunits. The apparent K(m) value for acryloyl-CoA was measured as 23 +/- 4 microm, independent of the concentration of the second substrate ammonia; k(cat)/K(m) was calculated as 10(7) m(-1) x s(-1). The apparent K(m) for ammonia was much higher, 70 +/- 5 mm at 150 microm acryloyl-CoA with a much lower k(cat)/K(m) of 4 x 10(3) m(-1) x s(-1). In the reverse reaction, a K(m) of 210 +/- 30 microM was obtained for beta-alanyl-CoA. The elimination of ammonia was inhibited by 70% at 100 mm ammonium chloride. The content of beta-alanyl-CoA:ammonia lyase in beta-alanine grown cells is about 100 times higher than that required to sustain the growth rate of the organism. It is therefore suggested that the enzyme is needed to bind acryloyl-CoA, in order to keep the toxic free form at a very low level. A formula was derived for the calculation of isomerization equilibra between L-alanine/beta-alanine or D-lactate/3-hydroxypropionate.

Subunit composition of the glycyl radical enzyme p-hydroxyphenylacetate decarboxylase

p-Hydroxyphenylacetate decarboxylase from Clostridium difficile catalyses the decarboxylation of p-hydroxyphenylacetate to yield the cytotoxic compound p-cresol. The three genes encoding two subunits of the glycyl-radical enzyme and the activating enzyme have been cloned and expressed in Escherichia coli. The recombinant enzymes were used to reconstitute a catalytically functional system in vitro. In contrast with the decarboxylase purified from C. difficile, which was an almost inactive homo-dimeric protein (beta(2)), the recombinant enzyme was a hetero-octameric (beta(4)gamma(4)), catalytically competent complex, which was activated using endogenous activating enzyme from C. difficile or recombinant activating enzyme to a specific activity of 7 U.mg(-1). Preliminary results suggest that phosphorylation of the small subunit is responsible for the change of the oligomeric state. These data point to an essential function of the small subunit of the decarboxylase and may indicate unique regulatory properties of the system.

Stereochemistry of hydrogen removal from the ‘unactivated’ C-3 position of 4-hydroxybutyryl-CoA catalysed by 4-hydroxybutyryl-CoA dehydratase

(R)- and (S)-gamma-[3-(2)H(1)]butyrolactones have been synthesised from (R)- and (S)-glycidol, respectively, and used to demonstrate that it is the pro-(S) hydrogen atom that is stereospecifically abstracted from C-3 of 4-hydroxybutyryl-CoA by 4-hydroxybutyryl-CoA dehydratase, and that this atom is not returned to C-4.

Acryloyl-CoA reductase from Clostridium propionicum. An enzyme complex of propionyl-CoA dehydrogenase and electron-transferring flavoprotein

Acryloyl-CoA reductase from Clostridium propionicum catalyses the irreversible NADH-dependent formation of propionyl-CoA from acryloyl-CoA. Purification yielded a heterohexadecameric yellow-greenish enzyme complex [(alpha2betagamma)4; molecular mass 600 +/- 50 kDa] composed of a propionyl-CoA dehydrogenase (alpha2, 2 x 40 kDa) and an electron-transferring flavoprotein (ETF; beta, 38 kDa; gamma, 29 kDa). A flavin content (90% FAD and 10% FMN) of 2.4 mol per alpha2betagamma subcomplex (149 kDa) was determined. A substrate alternative to acryloyl-CoA (Km = 2 +/- 1 microm; kcat = 4.5 s-1 at 100 microm NADH) is 3-buten-2-one (methyl vinyl ketone; Km = 1800 microm; kcat = 29 s-1 at 300 microm NADH). The enzyme complex exhibits acyl-CoA dehydrogenase activity with propionyl-CoA (Km = 50 microm; kcat = 2.0 s-1) or butyryl-CoA (Km = 100 microm; kcat = 3.5 s-1) as electron donor and 200 microm ferricenium hexafluorophosphate as acceptor. The enzyme also catalysed the oxidation of NADH by iodonitrosotetrazolium chloride (diaphorase activity) or by air, which led to the formation of H2O2 (NADH oxidase activity). The N-terminus of the dimeric propionyl-CoA dehydrogenase subunit is similar to those of butyryl-CoA dehydrogenases from several clostridia and related anaerobes (up to 55% sequence identity). The N-termini of the beta and gamma subunits share 40% and 35% sequence identities with those of the A and B subunits of the ETF from Megasphaera elsdenii, respectively, and up to 60% with those of putative ETFs from other anaerobes. Acryloyl-CoA reductase from C. propionicum has been characterized as a soluble enzyme, with kinetic properties perfectly adapted to the requirements of the organism. The enzyme appears not to be involved in anaerobic respiration with NADH or reduced ferredoxin as electron donors. There is no relationship to the trans-2-enoyl-CoA reductases from various organisms or the recently described acryloyl-CoA reductase activity of propionyl-CoA synthase from Chloroflexus aurantiacus.

A two [4Fe-4S]-cluster-containing ferredoxin as an alternative electron donor for 2-hydroxyglutaryl-CoA dehydratase from Acidaminococcus fermentans

The key step in the fermentation of glutamate by Acidaminococcus fermentans is a reversible syn-elimination of water from ( R)-2-hydroxyglutaryl-CoA to ( E)-glutaconyl-CoA catalyzed by 2-hydroxyglutaryl-CoA dehydratase, a two-component enzyme system. The actual dehydration is mediated by component D, which contains 1.0 [4Fe-4S](2+) cluster, 1.0 reduced riboflavin-5'-phosphate and about 0.1 molybdenum (VI) per heterodimer. The enzyme has to be activated by the extremely oxygen-sensitive [4Fe-4S](1+/2+)-cluster-containing homodimeric component A, which generates Mo(V) by an ATP/Mg(2+)-induced one-electron transfer. Previous experiments established that the hydroquinone state of a flavodoxin (m=14.6 kDa) isolated from A. fermentans served as one-electron donor of component A, whereby the blue semiquinone is formed. Here we describe the isolation and characterization of an alternative electron donor from the same organism, a two [4Fe-4S](1+/2+)-cluster-containing ferredoxin (m=5.6 kDa) closely related to that from Clostridium acidiurici. The protein was purified to homogeneity and almost completely sequenced; the magnetically interacting [4Fe-4S] clusters were characterized by EPR and Mössbauer spectroscopy. The redox potentials of the ferredoxin were determined as -405 mV and -340 mV. Growth experiments with A. fermentans in the presence of different iron concentrations in the medium (7-45 microM) showed that flavodoxin is the dominant electron donor protein under iron-limiting conditions. Its concentration continuously decreased from 3.5 micromol/g protein at 7 microM Fe to 0.02 micromol/g at 45 microM Fe. In contrast, the concentration of ferredoxin increased stepwise from about 0.2 micromol/g at 7-13 microM Fe to 1.1+/-0.1 micromol/g at 17-45 microM Fe.

Biochemical characterisation and genetic analysis of aureocin A53, a new, atypical bacteriocin from Staphylococcus aureus

Aureocin A53 is produced by Staphylococcus aureus A53. It is encoded on a 10.4 kb plasmid, pRJ9, and is active against Listeria monocytogenes. Aureocin A53 is a highly cationic 51-residue peptide containing ten lysine and five tryptophan residues. Aureocin A53 was purified to homogeneity by hydrophobic-interaction, cation-exchange, and reverse-phase chromatography. MALDI-TOF mass spectrometry yielded a molecular mass of 6012.5 Da, which was 28 Da higher than predicted from the structural gene sequence of the bacteriocin. The mass increment resulted from an N-formylmethionine residue, indicating that the aureocin A53 is synthesised and secreted without a typical bacteriocin leader sequence or sec-dependent signal peptide. The structural identity of aureocin A53 was verified by Edman sequencing after de-blocking with cyanogen bromide and extensive mass spectrometry analysis of enzymatically and laser-generated fragments. The complete sequence of pRJ9 was determined and none of the open reading frames identified in the vicinity of the structural gene aucA showed similarity to genes that are typically found in bacteriocin gene clusters. Thus, neither a dedicated protease or transporter, nor modifying enzymes and regulatory elements seemed to be involved in the production of aureocin A53. Further unique features that distinguish aureocin A53 from other peptide bacteriocins include remarkable protease stability and a defined, rigid structure in aqueous solution.

Propionate CoA-transferase from Clostridium propionicum. Cloning of gene and identification of glutamate 324 at the active site

Propionate CoA-transferase from Clostridium propionicum has been purified and the gene encoding the enzyme has been cloned and sequenced. The enzyme was rapidly and irreversibly inactivated by sodium borohydride or hydroxylamine in the presence of propionyl-CoA. The reduction of the thiol ester between a catalytic site glutamate and CoA with borohydride and the cleavage by hydroxylamine were used to introduce a site-specific label, which was followed by MALDI-TOF-MS. This allowed the identification of glutamate 324 at the active site. Propionate CoA-transferase and similar proteins deduced from the genomes of Escherichia coli, Staphylococcus aureus, Bacillus halodurans and Aeropyrum pernix are proposed to form a novel subclass of CoA-transferases. Secondary structure element predictions were generated and compared to known crystal structures in the databases. A high degree of structural similarity was observed between the arrangement of secondary structure elements in these proteins and glutaconate CoA-transferase from Acidaminococcus fermentans.

p-Hydroxyphenylacetate decarboxylase from Clostridium difficile. A novel glycyl radical enzyme catalysing the formation of p-cresol

The human pathogenic bacterium Clostridium difficile is a versatile organism concerning its ability to ferment amino acids. The formation of p-cresol as the main fermentation product of tyrosine by C. difficile is unique among clostridial species. The enzyme responsible for p-cresol formation is p-hydroxyphenylacetate decarboxylase. The enzyme was purified from C. difficile strain DMSZ 1296(T) and initially characterized. The N-terminal amino-acid sequence was 100% identical to an open reading frame in the unfinished genome of C. difficile strain 630. The ORF encoded a protein of the same size as the purified decarboxylase and was very similar to pyruvate formate-lyase-like proteins from Escherichia coli and Archaeoglobus fulgidus. The enzyme decarboxylated p-hydroxyphenylacetate (K(m) = 2.8 mM) and 3,4-dihydroxyphenylacetate (K(m) = 0.5 mM). It was competitively inhibited by the substrate analogues p-hydroxyphenylacetylamide and p-hydroxymandelate with K(i) values of 0.7 mM and 0.48 mM, respectively. The protein was readily and irreversibly inactivated by molecular oxygen. Although the purified enzyme was active in the presence of sodium sulfide, there are some indications for an as yet unidentified low molecular mass cofactor that is required for catalytic activity in vivo. Based on the identification of p-hydroxyphenylacetate decarboxylase as a novel glycyl radical enzyme and the substrate specificity of the enzyme, a catalytic mechanism involving ketyl radicals as intermediates is proposed.

The biosynthesis of methylated amino acids in the active site region of methyl-coenzyme M reductase

The global production of the greenhouse gas methane by methanogenic archaea reaches 1 billion tons per annum. The final reaction releasing methane is catalyzed by the enzyme methyl-coenzyme M reductase. The crystal structure of methyl-coenzyme M reductase from Methanobacterium thermoautotrophicum revealed the presence of five modified amino acids within the alpha-subunit and near the active site region. Four of these modifications were C-, N-, and S-methylations, two of which, 2-(S)-methylglutamine and 5-(S)-methylarginine, have never been encountered before. We have now confirmed these modifications by mass spectrometry of chymotryptic peptides. With methyl-coenzyme M reductase purified from cells grown in the presence of L-[methyl-D(3)]methionine, it was shown that the methyl groups of the modified amino acids are derived from the methyl group of methionine rather than from methyl-coenzyme M, an intermediate in methane formation. The D(3) labeling pattern was found to be qualitatively and quantitatively the same as in the two methyl groups of the methanogenic coenzyme F(430), which are known to be introduced via S-adenosylmethionine. From the results, it is concluded that the methyl groups of the modified amino acids in methyl-coenzyme M reductase are biosynthetically introduced by an S-adenosylmethionine-dependent post-translational modification. A mechanism for the methylation of glutamine at C-2 and of arginine at C-5 is discussed.

"ADP sulfurylase" from Thiobacillus denitrificans is an adenylylsulfate:phosphate adenylyltransferase and belongs to a new family of nucleotidyltransferases

During AMP-dependent sulfite oxidation by some sulfur bacteria, the liberation of sulfate from adenosine-5'-phosphosulfate (APS) is catalyzed by APS:phosphate adenylyltransferase (APAT). Here we report the first biochemical and genetic characterization of APAT. We isolated this enzyme from the chemolithoautotroph Thiobacillus denitrificans and cloned the corresponding gene. The enzyme is homodimeric with 41,387-Da subunits and exhibits a specific activity of 2100 micromol min(-1) mg(-1). The K(m) values are K(m(APS)) = 300 microM and K(m(P(i))) = 12 mM. Catalysis occurs by a ping-pong mechanism with a covalently bound AMP as reaction intermediate. The arsenolysis of APS, but not of ADP, CDP, GDP, UDP, or IDP, is also catalyzed, indicating a specific and unidirectional function. The former enzyme name ADP-sulfurylase implies that the reverse reaction is catalyzed; therefore, this name should not be used any longer. Histidine modification of APAT results in complete inactivation that can be suppressed by substrate addition. APAT is highly similar to galactose-1-phosphate uridylyltransferase and also related to Ap(4)A phosphorylase. Active site residues of galactose-1-phosphate uridylyltransferase are conserved in APAT and Ap(4)A phosphorylase, suggesting a histidine as the nucleotide-binding residue in all three enzymes, which together form a new family of nucleotidyltransferases.

Oxygen exchange between acetate and the catalytic glutamate residue in glutaconate CoA-transferase from Acidaminococcus fermentans. Implications for the mechanism of CoA-ester hydrolysis

The exchange of oxygen atoms between acetate, glutaryl-CoA, and the catalytic glutamate residue in glutaconate CoA-transferase from Acidaminococcus fermentans was analyzed using [(18)O(2)]acetate together with matrix-assisted laser desorption/ionization time of flight mass spectrometry of an appropriate undecapeptide. The exchange reaction was shown to be site-specific, reversible, and required both glutaryl-CoA and [(18)O(2)]acetate. The observed exchange is in agreement with the formation of a mixed anhydride intermediate between the enzyme and acetate. In contrast, with a mutant enzyme, which was converted to a thiol ester hydrolyase by replacement of the catalytic glutamate residue by aspartate, no (18)O uptake from H(2)(18)O into the carboxylate was detectable. This result is in accord with a mechanism in which the carboxylate of aspartate acts as a general base in activating a water molecule for hydrolysis of the thiol ester intermediate. This mechanism is further supported by the finding of a significant hydrolyase activity of the wild-type enzyme using acetyl-CoA as substrate, whereas glutaryl-CoA is not hydrolyzed. The small acetate molecule in the substrate binding pocket may activate a water molecule for hydrolysis of the nearby enzyme-CoA thiol ester.

Basidiolipids from Agaricus are novel immune adjuvants

The primary aim of the present study was to compare the immune adjuvanticity of two different groups of glycolipids, i.e., the newly discovered basidiolipids from Basidiomycete mushrooms (Bl-1, Bl-2, Bl-3, and Bl-4), and saponin fractions from Quillaja saponaria. The basidiolipids, though with differential effectiveness of the Bl-components, stimulated the expression of serum immune globulins in mice that recognized co-injected antigens, bovine serum albumin (BSA) or a keyhole-limpet hemocyanin-ganglioside Gfpt1 conjugate (KLH-Gfpt1), respectively. The immune adjuvanticity of the basidiolipids was comparable to that of acidic (QAS2, QAS5, QAS10), and novel neutral (QNS1, QNS2, QNS3) saponin compounds isolated and purified from Quillaja saponaria bark bulk material. Basidiolipids, as well as, the Q. saponin fractions were only marginally antigenic. MPL-A, by contrast, a comparable immune adjuvant, stimulated the expression of specific antibodies that recognized this glycophospholipid. Different from the Q. saponins with restricted toxicity, the basidiolipids displayed no toxic or hemolytic properties.

Novel glycoinositolphosphosphingolipids, basidiolipids, from Agaricus

From the edible mushroom, the basidiomycetes Agaricus bisporus and Agaricus campestris, a novel carbohydrate-homologous series of four glyco-inositol-phospho-sphingolipids, designated basidiolipids, was isolated and the constituents purified. The chemical structures of the basidiolipids were elucidated to be: Manpbeta1-2inositol1-phospho-ceramide, Galpalpha-6[Fucpalpha-2]Galpbeta-6Manpbeta-2i nositol1-phospho-ceramide, Galpalpha-6Galpalpha-6[Fucpalpha-2]Galpbeta- 6Manpbeta-2inositol1-phospho-ceramide and Galpalpha-6Galpalpha-6Galpalpha-6[Fucpalpha-2] Galpbeta-6Manpbeta-2ino sitol1-phospho-ceramide. All four glycolipids contained a ceramide which was composed of phytosphingosine and predominantly alpha-hydroxy-behenic and alpha-hydroxy-lignoceric acid.

A novel protein modification generating an aldehyde group in sulfatases: its role in catalysis and disease

In multiple sulfatase deficiency, a rare human lysosomal storage disorder, all known sulfatases are synthesized as catalytically poorly active polypeptides. Analysis of the latter has shown that they lack a protein modification that was detected in all members of the sulfatase family. This novel protein modification generates a 2-amino-3-oxopropanoic acid (C alpha-formylglycine) residue by oxidation of the thiol group of a cysteine that is conserved among all eukaryotic sulfatases. The oxidation occurs in the endoplasmic reticulum at a stage when the nascent polypeptide is not yet folded. The aldehyde is part of the catalytic site and is likely to act as an aldehyde hydrate. One of the geminal hydroxyl groups accepts the sulfate during sulfate ester cleavage leading to the formation of a covalently sulfated enzyme intermediate. The other hydroxyl is required for the subsequent elimination of the sulfate and regeneration of the aldehyde group. In some prokaryotic members of the sulfatase gene family, the DNA sequence predicts a serine residue, and not a cysteine. Analysis of one of these prokaryotic sulfatases, however, revealed the presence of the C alpha-formylglycine indicating that the aldehyde group is essential for all members of the sulfatase family and that it can be generated from either cysteine or serine.

Crystal structure of human arylsulfatase A: the aldehyde function and the metal ion at the active site suggest a novel mechanism for sulfate ester hydrolysis

Human lysosomal arylsulfatase A (ASA) is a prototype member of the sulfatase family. These enzymes require the posttranslational oxidation of the -CH2SH group of a conserved cysteine to an aldehyde, yielding a formylglycine. Without this modification sulfatases are catalytically inactive, as revealed by a lysosomal storage disorder known as multiple sulfatase deficiency. The 2.1 A resolution X-ray crystal structure shows an ASA homooctamer composed of a tetramer of dimers, (alpha 2)4. The alpha/beta fold of the monomer has significant structural analogy to another hydrolytic enzyme, the alkaline phosphatase, and superposition of these two structures shows that the active centers are located in largely identical positions. The functionally essential formylglycine is located in a positively charged pocket and acts as ligand to an octahedrally coordinated metal ion interpreted as Mg2+. The electron density at the formylglycine suggests the presence of a 2-fold disordered aldehyde group with the possible contribution of an aldehyde hydrate, -CH(OH)2, with gem-hydroxyl groups. In the proposed catalytic mechanism, the aldehyde accepts a water molecule to form a hydrate. One of the two hydroxyl groups hydrolyzes the substrate sulfate ester via a transesterification step, resulting in a covalent intermediate. The second hydroxyl serves to eliminate sulfate under inversion of configuration through C-O cleavage and reformation of the aldehyde. This study provides the structural basis for understanding a novel mechanism of ester hydrolysis and explains the functional importance of the unusually modified amino acid.

Sulfatases, trapping of the sulfated enzyme intermediate by substituting the active site formylglycine

Sulfatases contain an active site formylglycine residue that is generated by post-translational modification. Crystal structures of two lysosomal sulfatases revealed significant similarity to the catalytic site of alkaline phosphatase containing a serine at the position of formylglycine. To elucidate the catalytic mechanism of sulfate ester hydrolysis, the formylglycine of arylsulfatases A and B was substituted by serine. These mutants upon incubation with substrate were covalently sulfated at the introduced serine. This sulfated enzyme intermediate was stable at pH 5. At alkaline pH it was slowly hydrolyzed. These characteristics are analogous to that of alkaline phosphatase which forms a phosphoserine intermediate that is stable at pH 5, but is hydrolyzed at alkaline pH. In wild-type sulfatases the hydroxyl needed for formation of the sulfated enzyme intermediate is provided by the aldehyde hydrate of the formylglycine. The second, non-esterified hydroxyl of the aldehyde hydrate is essential for rapid desulfation of the enzyme at acidic pH, which most likely occurs by elimination. The lack of this second hydroxyl in the serine mutants explains the trapping of the sulfated enzyme intermediate. Thus, in acting as a geminal diol the formylglycine residue allows for efficient ester hydrolysis in an acidic milieu.

Arylsulfatase from Klebsiella pneumoniae carries a formylglycine generated from a serine

Eukaryotic sulfatases share an unusual posttranslational protein modification, which converts a cysteine into alpha-formylglycine. The alpha-formylglycine is essential for the catalytic activity. Klebsiella pneumoniae expresses an inducible arylsulfatase for which the DNA predicts a serine at the position occupied by the alpha-formylglycine residue in eukaryotic sulfatases. Structural analysis showed that the majority of the arylsulfatase polypeptides from K. pneumoniae carries the alpha-formylglycine, whereas the remaining arylsulfatase polypeptides contain the predicted serine residue. This demonstrates the evolutionary conservation between prokaryotes and eukaryotes of this novel protein modification that so far has been found only in sulfatases. alpha-Formylglycine in Klebsiella is generated from a serine and not from a cysteine as in eukaryotes.

The evolutionary conservation of a novel protein modification, the conversion of cysteine to serinesemialdehyde in arylsulfatase from Volvox carteri

A novel post-translational protein modification has recently been described in two human sulfatases, by which a cysteine is replaced by a serinesemialdehyde (2-amino-3-oxopropionic acid) residue [Schmidt, B., Selmer, T., Ingendoh, A. & von Figura, K. (1995) Cell 82, 271-278]. This cysteine is conserved among all known eukaryotic sulfatases. Here we report the presence of this modification in arylsulfatase from the green alga Volvox carteri. The evolutionary conservation of this novel protein modification between sulfatases of V. carteri and man lends further support to the assumption that this modification is required for the catalytic activity of sulfatases and may be present in all sulfatases of eukaryotic origin.

A novel amino acid modification in sulfatases that is defective in multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is a lysosomal storage disorder characterized by a decreased activity of all known sulfatases. The deficiency of sulfatases was proposed to result from the lack of a co- or posttranslational modification that is common to all sulfatases and required for their catalytic activity. Structural analysis of two catalytically active sulfatases revealed that a cysteine residue that is predicted from the cDNA sequence and conserved among all known sulfatases is replaced by a 2-amino-3-oxopropionic acid residue, while in sulfatases derived from MSD cells, this cysteine residue is retained. It is proposed that the co- or posttranslational conversion of a cysteine to 2-amino-3-oxopropionic acid is required for generating catalytically active sulfatases and that deficiency of this protein modification is the cause of MSD.

Glycosylation and phosphorylation of arylsulfatase A

The glycosylation and phosphorylation of the lysosomal enzyme arylsulfatase A was analyzed by a combination of metabolic labeling, tryptic fragmentation, mass spectrometry, and radiosequencing. The results demonstrate that all three potential N-glycosylation sites at Asn residues 158, 184, and 350 are utilized in arylsufatase A and carry high mannose or hybride type oligosaccharides. Phosphorylation of mannose residues is restricted to oligosaccharides at the first and third N-glycosylation site (Asn-158 and Asn-350). Both are phosphorylated with comparable efficiency. An earlier study had shown that a mutant arylsulfatase A containing only the second N-glycosylation site at Asn-184 folds correctly and is phosphorylated (Gieselmann, V., Schmidt, B., and von Figura, K. (1992) J. Biol. Chem. 267, 13262-13266). The lack of phosphorylation at Asn-184 in wild type arylsulfatase A therefore indicates that in vivo the presence of oligosaccharides can interfere with phosphorylation of other sites or that phosphorylation occurs in an ordered manner whereby phosphorylation of one site can affect the phosphorylation of another site.