scholarly journals Anthrose Biosynthetic Operon of Bacillus anthracis

2008 ◽  
Vol 190 (7) ◽  
pp. 2350-2359 ◽  
Author(s):  
Shengli Dong ◽  
Sylvia A. McPherson ◽  
Li Tan ◽  
Olga N. Chesnokova ◽  
Charles L. Turnbough ◽  
...  
Keyword(s):  
Bacillus Anthracis ◽  
Basal Layer ◽  
Side Chain ◽  
Biosynthetic Enzymes ◽  
Multiple Copies

ABSTRACT The exosporium of Bacillus anthracis spores consists of a basal layer and an external hair-like nap. The nap is composed primarily of the glycoprotein BclA, which contains a collagen-like region with multiple copies of a pentasaccharide side chain. This oligosaccharide possesses an unusual terminal sugar called anthrose, followed by three rhamnose residues and a protein-bound N-acetylgalactosamine. Based on the structure of anthrose, we proposed an enzymatic pathway for its biosynthesis. Examination of the B. anthracis genome revealed six contiguous genes that could encode the predicted anthrose biosynthetic enzymes. These genes are transcribed in the same direction and appear to form two operons. We introduced mutations into the B. anthracis chromosome that either delete the promoter of the putative upstream, four-gene operon or delete selected genes in both putative operons. Spores produced by strains carrying mutations in the upstream operon completely lacked or contained much less anthrose, indicating that this operon is required for anthrose biosynthesis. In contrast, inactivation of the downstream, two-gene operon did not alter anthrose content. Additional experiments confirmed the organization of the anthrose operon and indicated that it is transcribed from a σE-specific promoter. Finally, we demonstrated that anthrose biosynthesis is not restricted to B. anthracis as previously suggested.

scholarly journals Identification of the UDP-N-Acetylglucosamine 4-Epimerase Involved in Exosporium Protein Glycosylation in Bacillus anthracis

2009 ◽  
Vol 191 (22) ◽  
pp. 7094-7101 ◽  
Author(s):  
Shengli Dong ◽  
Olga N. Chesnokova ◽  
Charles L. Turnbough ◽  
David G. Pritchard
Keyword(s):  
Escherichia Coli ◽  
Bacillus Anthracis ◽  
Basal Layer ◽  
Amino Sugar ◽  
Protein Glycosylation ◽  
Side Chains ◽  
Protein Backbone ◽  
Gene Encoding ◽  
Multiple Copies ◽  
Late Stages

ABSTRACT Spores of Bacillus anthracis, the causative agent of anthrax, are enclosed by a loosely fitting exosporium composed of a basal layer and an external hair-like nap. The filaments of the nap are formed by trimers of the collagen-like glycoprotein BclA. The side chains of BclA include multiple copies of two linear rhamnose-containing oligosaccharides, a trisaccharide and a pentasaccharide. The pentasaccharide terminates with the unusual deoxyamino sugar anthrose. Both oligosaccharide side chains are linked to the BclA protein backbone through an N-acetylgalactosamine (GalNAc) residue. To identify the gene encoding the epimerase required to produce GalNAc for BclA oligosaccharide biosynthesis, three annotated UDP-glucose 4-epimerase genes of B. anthracis were cloned and expressed in Escherichia coli. The candidate proteins were purified, and their enzymatic activities were assessed. Only two proteins, encoded by the BAS5114 and BAS5304 genes (B. anthracis Sterne designations), exhibited epimerase activity. Both proteins were able to convert UDP-glucose (Glc) to UDP-Gal, but only the BAS5304-encoded protein could convert UDP-GlcNAc to UDP-GalNAc, indicating that BAS5304 was the gene sought. Surprisingly, spores produced by a mutant strain lacking the BAS5304-encoded enzyme still contained normal levels of BclA-attached oligosaccharides. However, monosaccharide analysis of the oligosaccharides revealed that GlcNAc had replaced GalNAc. Thus, while GalNAc appears to be the preferred amino sugar for the linkage of oligosaccharides to the BclA protein backbone, in its absence, GlcNAc can serve as a substitute linker. Finally, we demonstrated that the expression of the BAS5304 gene occurred in a biphasic manner during both the early and late stages of sporulation.

scholarly journals Characterization of the Enzymes Encoded by the Anthrose Biosynthetic Operon of Bacillus anthracis

2010 ◽  
Vol 192 (19) ◽  
pp. 5053-5062 ◽  
Author(s):  
Shengli Dong ◽  
Sylvia A. McPherson ◽  
Yun Wang ◽  
Mei Li ◽  
Pengfei Wang ◽  
...  
Keyword(s):  
Bacillus Anthracis ◽  
Biosynthetic Pathway ◽  
Basal Layer ◽  
Side Chain ◽  
Side Chains ◽  
Aminotransferase Activity ◽  
Acyltransferase Activity ◽  
Hydratase Activity ◽  
Etiological Agents

ABSTRACT Bacillus anthracis spores, the etiological agents of anthrax, possess a loosely fitting outer layer called the exosporium that is composed of a basal layer and an external hairlike nap. The filaments of the nap are formed by trimers of the collagenlike glycoprotein BclA. Multiple pentasaccharide and trisaccharide side chains are O linked to BclA. The nonreducing terminal residue of the pentasaccharide side chain is the unusual sugar anthrose. A plausible biosynthetic pathway for anthrose biosynthesis has been proposed, and an antABCD operon encoding four putative anthrose biosynthetic enzymes has been identified. In this study, we genetically and biochemically characterized the activities of these enzymes. We also used mutant B. anthracis strains to determine the effects on BclA glycosylation of individually inactivating the genes of the anthrose operon. The inactivation of antA resulted in the appearance of BclA pentasaccharides containing anthrose analogs possessing shorter side chains linked to the amino group of the sugar. The inactivation of antB resulted in BclA being replaced with only trisaccharides, suggesting that the enzyme encoded by the gene is a dTDP-β-l-rhamnose α-1,3-l-rhamnosyl transferase that attaches the fourth residue of the pentasaccharide side chain. The inactivation of antC and antD resulted in the disappearance of BclA pentasaccharides and the appearance of a tetrasaccharide lacking anthrose. These phenotypes are entirely consistent with the proposed roles for the antABCD-encoded enzymes in anthrose biosynthesis. Purified AntA was then shown to exhibit β-methylcrotonyl-coenzyme A (CoA) hydratase activity, as we predicted. Similarly, we confirmed that purified AntC had aminotransferase activity and that purified AntD displayed N-acyltransferase activity.

scholarly journals An Unusual Mechanism of Isopeptide Bond Formation Attaches the Collagenlike Glycoprotein BclA to the Exosporium of Bacillus anthracis

mBio ◽  
2011 ◽  
Vol 2 (3) ◽  
Author(s):  
Li Tan ◽  
Mei Li ◽  
Charles L. Turnbough
Keyword(s):  
Bacillus Anthracis ◽  
Bond Formation ◽  
Basal Layer ◽  
Side Chain ◽  
Cross Linking ◽  
Amino Group ◽  
Content Type ◽  
Isopeptide Bond ◽  
Isopeptide Bonds

ABSTRACTThe outermost exosporium layer of spores ofBacillus anthracis, the causative agent of anthrax, is comprised of a basal layer and an external hairlike nap. The nap includes filaments composed of trimers of the collagenlike glycoprotein BclA. Essentially all BclA trimers are tightly attached to the spore in a process requiring the basal layer protein BxpB (also called ExsFA). Both BclA and BxpB are incorporated into stable, high-molecular-mass complexes, suggesting that BclA is attached directly to BxpB. The 38-residue amino-terminal domain of BclA, which is normally proteolytically cleaved between residues 19 and 20, is necessary and sufficient for basal layer attachment. In this study, we demonstrate that BclA attachment occurs through the formation of isopeptide bonds between the free amino group of BclA residue A20 and a side chain carboxyl group of an acidic residue of BxpB. Ten of the 13 acidic residues of BxpB can participate in isopeptide bond formation, and at least three BclA polypeptide chains can be attached to a single molecule of BxpB. We also demonstrate that similar cross-linking occursin vitrobetween purified recombinant BclA and BxpB, indicating that the reaction is spontaneous. The mechanism of BclA attachment, specifically, the formation of a reactive amino group by proteolytic cleavage and the promiscuous selection of side chain carboxyl groups of internal acidic residues, appears to be different from other known mechanisms for protein cross-linking through isopeptide bonds. Analogous mechanisms appear to be involved in the cross-linking of other spore proteins and could be found in unrelated organisms.IMPORTANCEIsopeptide bonds are protein modifications found throughout nature in which amide linkages are formed between functional groups of two amino acids, with at least one of the functional groups provided by an amino acid side chain. Isopeptide bonds generate cross-links within and between proteins that are necessary for proper protein structure and function. In this study, we discovered that BclA, the dominant structural protein of the external nap ofBacillus anthracisspores, is attached to the underlying exosporium basal layer protein BxpB via isopeptide bonds formed through a mechanism fundamentally different from previously described mechanisms of isopeptide bond formation. The most unusual features of this mechanism are the generation of a reactive amino group by proteolytic cleavage and promiscuous selection of acidic side chains. This mechanism, which apparently relies only on short peptide sequences in protein substrates, could be a general mechanismin vivoand adapted for protein cross-linkingin vitro.

scholarly journals The ExsY Protein Is Required for Complete Formation of the Exosporium of Bacillus anthracis

2006 ◽  
Vol 188 (21) ◽  
pp. 7440-7448 ◽  
Author(s):  
Jeremy A. Boydston ◽  
Ling Yue ◽  
John F. Kearney ◽  
Charles L. Turnbough
Keyword(s):  
Bacillus Anthracis ◽  
Solid Medium ◽  
Basal Layer ◽  
Wild Type ◽  
Nucleoside Hydrolase ◽  
Spore Resistance ◽  
Normal Hair ◽  
Spore Outgrowth ◽  
Microscopic Inspection ◽  
Complete Formation

ABSTRACT The outermost layer of the Bacillus anthracis spore is the exosporium, which is composed of a paracrystalline basal layer and an external hair-like nap. The filaments of the nap are formed by a collagen-like glycoprotein called BclA, while the basal layer contains several different proteins. One of the putative basal layer proteins is ExsY. In this study, we constructed a ΔexsY mutant of B. anthracis, which is devoid of ExsY, and examined the assembly of the exosporium on spores produced by this strain. Our results show that exosporium assembly on ΔexsY spores is aberrant, with assembly arrested after the formation of a cap-like fragment that covers one end of the forespore—always the end near the middle of the mother cell. The cap contains a normal hair-like nap but an irregular basal layer. The cap is retained on spores prepared on solid medium, even after spore purification, but it is lost from spores prepared in liquid medium. Microscopic inspection of ΔexsY spores prepared on solid medium revealed a fragile sac-like sublayer of the exosporium basal layer, to which caps were attached. Examination of purified ΔexsY spores devoid of exosporium showed that they lacked detectable levels of BclA and the basal layer proteins BxpB, BxpC, CotY, and inosine-uridine-preferring nucleoside hydrolase; however, these spores retained half the amount of alanine racemase presumed to be associated with the exosporium of wild-type spores. The ΔexsY mutation did not affect spore production and germination efficiencies or spore resistance but did influence the course of spore outgrowth.

scholarly journals Crystal Structure of Bacillus anthracis Dihydrofolate Reductase with the Dihydrophthalazine-Based Trimethoprim Derivative RAB1 Provides a Structural Explanation of Potency and Selectivity

2009 ◽  
Vol 53 (7) ◽  
pp. 3065-3073 ◽  
Author(s):  
Christina R. Bourne ◽  
Richard A. Bunce ◽  
Philip C. Bourne ◽  
K. Darrell Berlin ◽  
Esther W. Barrow ◽  
...  
Keyword(s):  
Bacillus Anthracis ◽  
Dihydrofolate Reductase ◽  
Active Site ◽  
Inhibitory Concentration ◽  
Side Chain ◽  
Natural Substrate ◽  
X Ray Diffraction ◽  
Structural Explanation ◽  
X Ray ◽  
Hydrophobic Anchor

ABSTRACT Bacillus anthracis possesses an innate resistance to the antibiotic trimethoprim due to poor binding to dihydrofolate reductase (DHFR); currently, there are no commercial antibacterials that target this enzyme in B. anthracis. We have previously reported a series of dihydrophthalazine-based trimethoprim derivatives that are inhibitors for this target. In the present work, we have synthesized one compound (RAB1) displaying favorable 50% inhibitory concentration (54 nM) and MIC (≤12.8 μg/ml) values. RAB1 was cocrystallized with the B. anthracis DHFR in the space group P212121, and X-ray diffraction data were collected to a 2.3-Å resolution. Binding of RAB1 causes a conformational change of the side chain of Arg58 and Met37 to accommodate the dihydrophthalazine moiety. Unlike the natural substrate or trimethoprim, the dihydrophthalazine group provides a large hydrophobic anchor that embeds within the DHFR active site and accounts for its selective inhibitory activity against B. anthracis.

scholarly journals Orientation within the Exosporium and Structural Stability of the Collagen-Like Glycoprotein BclA of Bacillus anthracis

2005 ◽  
Vol 187 (15) ◽  
pp. 5310-5317 ◽  
Author(s):  
Jeremy A. Boydston ◽  
Ping Chen ◽  
Christopher T. Steichen ◽  
Charles L. Turnbough
Keyword(s):  
Electron Microscopy ◽  
Escherichia Coli ◽  
Monoclonal Antibodies ◽  
Bacillus Anthracis ◽  
Triple Helix ◽  
Thermal Denaturation ◽  
Sodium Dodecyl ◽  
Basal Layer ◽  
Structural Data ◽  
Immunogold Electron Microscopy

ABSTRACT Bacillus anthracis spores, which cause anthrax, are enclosed by an exosporium consisting of a basal layer and an external hair-like nap. The filaments of the nap are composed of BclA, a glycoprotein containing distinct N-terminal (NTD) and C-terminal (CTD) domains separated by an extended collagen-like central region. In this study, we used immunogold electron microscopy to show that the CTD of BclA forms the distal end of each filament of the hair-like nap, indicating that the NTD is attached to the basal layer. Ten randomly chosen anti-BclA monoclonal antibodies, raised against spores or exosporium, reacted with the CTD, consistent with its exterior location. We showed that recombinant BclA (rBclA), encoded by the B. anthracis Sterne strain and synthesized in Escherichia coli, forms a collagen-like triple helix as judged by collagenase sensitivity and circular dichroism spectroscopy. In contrast, native BclA in spores was resistant to collagenase digestion. Thermal denaturation studies showed that the collagen-like region of rBclA exhibited a melting temperature (T m ) of 37°C, like mammalian collagen. However, rBclA trimers exhibited T m values of 84°C and 95°C in buffer with and without sodium dodecyl sulfate, respectively. CTD trimers exhibited the same T m values, indicating that the high temperature and detergent resistances of rBclA were due to strong CTD interactions. We observed that CTD trimers are resistant to many proteases and readily form large crystalline sheets. Structural data indicate that the CTD is composed of multiple beta strands. Taken together, our results suggest that BclA and particularly its CTD form a rugged shield around the spore.

scholarly journals Immunogens related to the synthetic tetrasaccharide side chain of the Bacillus anthracis exosporium

2007 ◽  
Vol 15 (12) ◽  
pp. 4283-4310 ◽  
Author(s):  
Rina Saksena ◽  
Roberto Adamo ◽  
Pavol Kováč
Keyword(s):  
Bacillus Anthracis ◽  
Side Chain

scholarly journals Sortase C-Mediated Anchoring of BasI to the Cell Wall Envelope of Bacillus anthracis

2007 ◽  
Vol 189 (17) ◽  
pp. 6425-6436 ◽  
Author(s):  
Luciano A. Marraffini ◽  
Olaf Schneewind
Keyword(s):  
Cell Wall ◽  
Bacillus Anthracis ◽  
Active Site ◽  
Diaminopimelic Acid ◽  
Side Chain ◽  
Carboxyl Group ◽  
Amino Group ◽  
Active Site Cysteine ◽  
New Hosts ◽  
Host Death

ABSTRACT Vegetative forms of Bacillus anthracis replicate in tissues of an infected host and precipitate lethal anthrax disease. Upon host death, bacilli form dormant spores that contaminate the environment, thereby gaining entry into new hosts where spores germinate and once again replicate as vegetative forms. We show here that sortase C, an enzyme that is required for the formation of infectious spores, anchors BasI polypeptide to the envelope of predivisional sporulating bacilli. BasI anchoring to the cell wall requires the active site cysteine of sortase C and an LPNTA motif sorting signal at the C-terminal end of the BasI precursor. The LPNTA motif of BasI is cleaved between the threonine (T) and the alanine (A) residue; the C-terminal carboxyl group of threonine is subsequently amide linked to the side chain amino group of diaminopimelic acid within the wall peptides of B. anthracis peptidoglycan.

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