Refine
Year of publication
- 2015 (5) (remove)
Document Type
- Doctoral Thesis (3)
- Article (2)
Has Fulltext
- yes (5)
Is part of the Bibliography
- no (5)
Keywords
- - (2)
- Pneumokokken (2)
- 1-(S)-Phenylethanol (1)
- 1-Phenylethanol (1)
- 1-phenylethanol (1)
- Alkoholdehydrogenasen (1)
- Arginin (1)
- Arxula adeninivorans (1)
- Carboxypeptidase (1)
- Hefe (1)
Institute
- Institut für Mikrobiologie - Abteilung für Genetik & Biochemie (5) (remove)
Publisher
Streptococcus pneumoniae (pneumococci) are lancet-shaped, Gram-positive, alpha-hemolytic, facultative anaerobic human specific commensals of the upper and lower respiratory tract. Pneumococci may convert to pathogenic bacteria and spread to the lungs and blood. In different population groups, such as children, the elderly and immunocompromised individuals, pneumococci can cause local infections such as bronchitis, rhinitis, acute sinusitis, and otitis media as well as life-threatening invasive diseases such as community-acquired pneumonia, sepsis and meningitis. Pneumococci are surrounded by a rigid and complex exoskeleton, the peptidoglycan, also referred to as murein sacculus. The peptidoglycan (PNG) protects the cells from rupture by osmotic pressure and maintains their characteristic shape. The PNG is a heteropolymer made up of glycan strands that are cross-linked by short peptides and during growth the existing murein is continuously hydrolyzed by specific lytic enzymes to enable the insertion of new peptidoglycan. Bacterial cell-wall hydrolases are essential for peptidoglycan turnover and crucial to preserve cell shape. The D,D-carboxypeptidase DacA and L,D-carboxypeptidase DacB of Streptococcus pneumoniae function in a sequential manner. This study determined the crystal structure of the surface-exposed lipoprotein DacB, which differs considerably from the DacA structure. DacB contains a Zn2+ ion in its catalytic center located in the middle of a fully exposed, large groove. Two different conformations with differently arranged active site topology were identified. In addition the critical residues for catalysis and substrate specificity were identified. Deficiency in DacA or DacB resulted in a modified peptidoglycan peptide composition and led to an altered cell shape of the dac-mutants. In contrast, lgt-mutant lacking lipoprotein diacylglyceryl transferase activity required for proper lipoprotein maturation retained L,D-carboxypeptidase activity and showed an intact murein sacculus. Furthermore, this study demonstrated the pathophysiological effects of disordered DacA or DacB activities. Real-time bioimaging of intranasally infected mice indicated a substantially attenuated virulence of dacB- and dacAdacB-mutants pneumococci, while loss of function of DacA had no significant effect. In addition, uptake of these mutants by professional phagocytes was enhanced, while their adherence to lung epithelial cells was decreased. The second part of this study focused on the functional and structure determination of the soluble dimeric pneumococcal lipoprotein PccL. Because of its calycin fold and structural homology with the lipocalin YxeF from Bacillus subtilis, PccL was introduced as the first member of the lipocalin protein family in pneumococci and named “PccL” (Pneumococcal calycin fold containing Lipoprotein). Similar to other lipocalins, the distinct beta-barrel, which is open at one end, is significantly conserved in PccL. Moreover, the application of the in vivo acute pneumonia mouse infection model and the in vitro phagocytosis as well as adherence invasion studies revealed considerable differences in colonization and invasive infection between the wild-type D39 and the pccL-mutant. In conclusion, this study characterized the crucial role of pneumococcal carboxypeptidases DacA and DacB for PGN architecture, bacterial shape and pathogenesis. By applying in vivo and in vitro approaches, a close relationship between PGN metabolism and pathophysiological effects was discovered. In addition, the high resolution structure of DacB has been solved and analyzed and a structure model with a resolution of 2.0 Å is provided. Furthermore, analysis of the PGN composition was applied to indicate the impact of an impaired lipoprotein biogenesis pathway on localization and activity of DacB. The major impact of carboxypeptidases on cell shape and virulence proposes DacB as a promising target for the development of novel drugs or due to its surface exposition also as a promising vaccine candidate. PccL is the first pneumococcal lipocalin-like protein and this study indicated its contribution to pneumococcal virulence. However, the mechanism and the mode of action of PccL are still unknown and have to be deciphered in further studies.
Die ADHs aus Rhodococcus ruber (RrADH) und Lactobacillus brevis (LbADH) wurden erstmals in der Hefe Arxula adeninivorans (Blastobotrys adeninivorans) hergestellt und zur Synthese von enantiomerenreinen 1-Phenylethanol eingesetzt. Die entsprechenden Gene wurden hierfür mit dem starken konstitutiven TEF1-Promotor und dem PHO5-Terminator flankiert und unter Nutzung der etablierten Xplor2®-Transformations-/Expressionsplattform in der Hefe exprimiert. Die erhaltenen selektierten Transformanden wiesen dabei ADH-Aktivitäten von 21 bzw. 320 U g-1 dcw für die Reduktion von Acetophenon zu 1-Phenylethanol in Schüttelkultur auf. RrADH und LbADH sind für die Reduktion von Acetophenon und Acetophenon-Derivaten, alpha-Ketoestern und aliphatischen Ketonen geeignet. Die RrADH synthetisiert (S)-konfigurierte Alkohole und ist NAD+/NADH-abhängig, während die LbADH die Reduktion von Acetophenon zu 1-(R)-Phenylethanol mithilfe des Cofaktors NADPH katalysiert. Rohextrakt des RrADH produzierenden Hefestamms konnte erfolgreich für die Synthese von enantiomerenreinem 1-(S)-Phenylethanol mit einer Ausbeute von 90 % und einem Enantiomerenüberschuss (ee) von >99 % über Substrat-gekoppelte Regeneration mit Isopropanol eingesetzt werden. Die Erhöhung der Ausbeute auf 100 % gelang durch Enzym-gekoppelte Regenerierung des Cofaktors NADH mit der GDH aus Bacillus megaterium (Bm) für RrADH bzw. NADPH mit der BmGDH und G6PDH aus Bacillus pumilus (Bp) für LbADH katalysierte Reaktionen. ADHs und Cofaktor-regenerierende Enzyme wurden simultan durch die konstitutive Coexpression der entsprechenden Gene in A. adeninivorans für die Synthese von enantiomerenreinem 1-Phenylethanol hergestellt. Die Enzymrohextrakte der RrADH-BmGDH, LbADH-BmGDH und LbADH-BpG6PDH produzierenden Hefestämme katalysieren ohne Ausnahme die Synthese des jeweiligen Enantiomers von 1-Phenylethanol mit ee >99 % und Ausbeuten von 100 % für Substratkonzentrationen bis 40 mM. Nach der Extraktion des 1-Phenylethanols liegt dieses chemisch rein vor, sodass aufwendige Aufarbeitungs- und Reinigungsschritte erspart bleiben. GDH bzw. G6PDH sind hervorragend für die Regeneration von NADH und NADPH bzw. ausschließlich letzterem geeignet. Dabei wurden standardmäßig 40 mol 1-Phenylethanol pro Mol NAD+ oder NADP+ erreicht. Auch intakte Hefezellen der rekombinanten ADH und BmGDH bzw. BpG6PDH synthetisierenden Stämme wurden für die Synthese von 1-(S)- bzw. 1-(R)-Phenylethanol verwendet. Nach Permeabilisierung mit Triton X-100 wiesen sie vergleichbare Aktivitäten zu den entsprechenden Rohextrakten auf. Der RrADH-BmGDH produzierende Stamm synthetisiert 1-(S)-Phenylethanol mit einer Aktivität von 20 U g-1 dcw, während die LbADH-BmGDH und LbADH-BpG6PDH Hefestämme sogar 45,6 und 87,9 U g-1 dcw lieferten. Die Ausbeuten und ee waren im Vergleich zu den Rohextrakten ähnlich. Die Erhöhung der Konzentration des Ausgangsstoffs Acetophenon reduzierte unabhängig von den verwendeten Enzymen die erhaltene Ausbeute. Die katalytische Produktivität der Biokatalysatoren wurde durch ihre Wiederverwendung erhöht. Hierfür wurden permeabilisierte Zellen, die einfach aus der Syntheselösung abzentrifugiert werden können, genutzt. Außerdem konnten der Rohextrakt und die Zellen nach ihrem Einschluss in unlösliches Calciumalginat in Form von kleinen Kügelchen aus der Synthese abfiltriert und wiederverwendet werden. Permeabilisierte Zellen und Immobilisate wurden wiederholt für die Reduktion von Acetophenon zu 1-Phenylethanol eingesetzt, wobei immobilisierter Rohextrakt und Zellen für drei bis maximal sechs Synthesezyklen verwendet werden konnten. Immobilisierte und permeabilisierte Zellen sind wesentlich stabiler. Sie können ohne erhebliche Aktivitätsverluste 14 (LbADH-BpG6PDH), 29 (RrADH-BmGDH) bzw. mehr als 50 Mal (LbADH-BmGDH) wiederholt zur Acetophenon-Reduktion eingesetzt werden. Auf ihrer Grundlage wurde ein erster Reaktor für die semi-kontinuierliche Synthese von 1-(R)-Phenylethanol im Labormaßstab konstruiert und in Betrieb genommen. Es konnten 206 mol 1-(R)-Phenylethanol pro Mol NADP+ und 12,78 g 1-(R)-Phenylethanol mit einem ee von 100 % und einer Raum-Zeit-Ausbeute von 9,74 g L-1 d-1 oder 406 g kg-1 dcw d-1 erhalten werden. Weitere Optimierungen der Hefestämme, Reaktionsbedingungen und Reaktionsführung sind zur Erhöhung der Ausbeute und zum Erreichen vergleichbarer Produktivität mit derzeitigen Syntheseprozessen für 1-Phenylethanol nötig. Der ee ist bereits optimal. Zusammenfassend ist A. adeninivorans ein hervorragender Wirt zur Herstellung von ADHs für die Synthese enantiomerenreiner Alkohole wie 1-(S)- und 1-(R)-Phenylethanol. Nach Extraktion liegt das Produkt rein und mit optimalen ee vor. Durch die in dieser Arbeit gezeigten Untersuchungen können bisher chemische Synthesen durch enzymatische Reaktionen unter Einsatz von ADHs, deren Produktion in A. adeninivorans erfolgte, ersetzt werden, was Kosten und natürlichen Ressourcen spart.
The influence of regulatory proteins on the physiology and virulence of Streptococcus pneumoniae
(2015)
In conclusion, this work identifies the regulator ArgR2 as activator of the S. pneumoniae TIGR4 arginine deiminase system and arginine-ornithine transporter ArcD, which is needed for uptake of the essential amino acid arginine. Although ArgR2 activates ArcD expression and uptake of arginine is required to maintain pneumococcal fitness, the deficiency of ArgR2 increases TIGR4 virulence under in vivo conditions, suggesting that other factors regulated by ArgR2 counterbalance the reduced uptake of arginine by ArcD. Thus this works illustrates that the physiological homeostasis of pneumococci is complex and that ArgR2 plays a key role in maintaining bacterial fitness. Moreover, Rex was identified as a regulator of housekeeping genes including genes encoding glycolytic enzymes. In vitro studies and gene expression analyses suggested that the regulator Rex does not have an influence on the physiology of S. pneumoniae. However, a co-infection experiment demonstrated that Rex is involved in maintaining pneumococcal fitness and robustness under in vivo conditions.
Invasion of the bacterial pathogen Listeria monocytogenes into human host cells requires specialized surface molecules for attachment and induction of phagocytosis. However, efficient invasion is also dependent on factors with house-keeping functions, such as SecA2-dependent secretion of autolysins for post-divisional segregation of daughter cells. Mutations in this pathway prevent degradation of peptidoglycan cross-walls, so that long cell chains are formed that cannot be phagocytosed. The extreme chaining of such mutants manifests as rough colony phenotype. One rough clone was isolated from a transposon library with a transposon insertion in the uncharacterized lmo0720 gene (lftS) together with a spontaneous point mutation in the secA2 gene. We separated both mutations and demonstrated that this point mutation in the intramolecular regulator 2 domain of SecA2 was sufficient to inactivate the protein. In contrast, lftS deletion did not cause a ΔsecA2-like phenotype. lftS is located in an operon with lftR (lmo0719), encoding a PadR-like transcriptional regulator, and lftR deletion affected growth, invasion and day-light dependent coordination of swarming. Inactivation of lftS partially suppressed these phenotypes, suggesting a functional relationship between LftR and LftS. However, the invasion defect of the ΔlftR mutant was only marginally suppressed by lftS removal. LftR regulates expression of the lmo0979–0980 (lieAB) operon, encoding a putative multidrug resistance transporter and lieAB transcription was strongly upregulated in the absence of LftR. Deletion of lieAB in the ΔlftR background restores wild type-like invasion levels. Hence, we conclude that tight transcriptional repression of the lieAB operon is essential for efficient listerial host cell invasion.
Certain pathogenic bacteria adopt an intracellular lifestyle and proliferate in eukaryotic host cells. The intracellular niche protects the bacteria from cellular and humoral components of the mammalian immune system, and at the same time, allows the bacteria to gain access to otherwise restricted nutrient sources. Yet, intracellular protection and access to nutrients comes with a price, i.e., the bacteria need to overcome cell-autonomous defense mechanisms, such as the bactericidal endocytic pathway. While a few bacteria rupture the early phagosome and escape into the host cytoplasm, most intracellular pathogens form a distinct, degradation-resistant and replication-permissive membranous compartment. Intracellular bacteria that form unique pathogen vacuoles include Legionella, Mycobacterium, Chlamydia, Simkania, and Salmonella species. In order to understand the formation of these pathogen niches on a global scale and in a comprehensive and quantitative manner, an inventory of compartment-associated host factors is required. To this end, the intact pathogen compartments need to be isolated, purified and biochemically characterized. Here, we review recent progress on the isolation and purification of pathogen-modified vacuoles and membranes, as well as their proteomic characterization by mass spectrometry and different validation approaches. These studies provide the basis for further investigations on the specific mechanisms of pathogen-driven compartment formation.