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- Svedendahl, Maria
(författare)
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Exploring Conjugate Addition Activity in Pseudozyma antarctica Lipase B
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multifunctional enzymes have alternative functions or activities, known as “moonlighting” or “promiscuous”, which are often hidden behind a native enzyme activity and therefore only visible under special environmental conditions. In this thesis, the active-site of Pseudozyma (formerly Candida) antarctica lipase B was explored for a promiscuous conjugate addition activity. Pseudozyma antarctica lipase B is a lipase industrially used for hydrolysis or transacylation reactions. This enzyme contains a catalytic triad, Ser105-His224-Asp187, where a nucleophilic attack from Ser105 on carboxylic acid/ester substrates cause the formation of an acyl enzyme. For conjugate addition activity in Pseudozyma antarctica lipase B, replacement of Ser105 was assumed necessary to prevent competing hemiacetal formation. However, experiments revealed conjugate addition activity in both wild-type enzyme and the Ser105Ala variant. Enzyme-catalyzed conjugate additions were performed by adding sec-amine, thiols or 1,3-dicarbonyl compounds to various α,β-unsaturated carbonyl compounds in both water or organic solvent. The reactions followed Michaelis-Menten kinetics and the native ping pong bi bi reaction mechanism of Pseudozyma antarctica lipase B for hydrolysis/transacylation was rerouted to a novel ordered bi uni reaction mechanism for conjugate addition (Paper I, II, III). The lipase hydrolysis activity was suppressed more than 1000 times by the replacement of the nucleophilic Ser105 to Ala (Paper III).
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| 2. |
- Norberg, Oscar, 1982-
(författare)
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Photochemical Ligation Techniques for Carbohydrate Biosensors and Protein Interaction Studies
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the development of surface ligation techniques for the preparation of carbohydrate biosensors. Several methodologies were developed based on efficient photochemical insertion reactions which quickly functionalize polymeric materials, with either carbohydrates or functional groups such as alkynes or alkenes. The alkyne/alkene surfaces were then treated with carbohydrate azides or thiols and reacted under chemoselective Cu-catalyzed azide-alkyne cycloaddition (CuAAC) or photo-radical thiol-ene/yne click chemistry, thus creating a range of carbohydrate biosensor surfaces under ambient conditions. The methodologies were evaluated by quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) flow through instrumentations with recurring injections of a range of lectins, allowing for real-time analysis of the surface interactions. The developed methods were proven robust and versatile, and the generated carbohydrate biosensors showed high specificities and good capacities for lectin binding. The methods were then used to investigate how varying the glycan linker length and/or a sulfur-linkage affect the subsequent protein binding. The survey was further explored by investigating the impact of sulfur in glycosidic linkages on protein binding, through competition assays with various O/S-linked disaccharides in solution interactions with lectins.
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| 3. |
- Pei, Zhichao, 1965-
(författare)
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Carbohydrate Synthesis and Study of Carbohydrate-Lectin Interactions Using QCM Biosensors and Microarray Technologies
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Interactions between carbohydrates and proteins are increasingly being recognized as crucial in many biological processes, such as cellular adhesion and communication. In order to investigate the interactions of carbohydrates and proteins, the development of efficient analytic technologies, as well as novel strategies for the synthesis of carbohydrates, have to be explored. To date, several methods have been exploited to analyze interactions of carbohydrates and proteins, for example, biosensors, nuclear magnetic resonance (NMR); enzyme-linked immunosorbent assays (ELISA), X-ray crystallography and array technologies. This thesis describes the development of novel strategies for the synthesis of carbohydrates, as well as new efficient strategies to Quartz Crystal Microbalance- (QCM-) biosensors and carbohydrate microarrays technologies. These methodologies have been used to probe carbohydrate-lectin-interactions for a range of plant and animal lectins.
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