| 1. |
- Zumarraga, Miren, et al.
(författare)
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Altering the laccase functionality by in vivo assembly of mutant libraries with different mutational spectra
- 2008
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Ingår i: Proteins. - : Wiley. - 0887-3585. ; 71:1, s. 250-260
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Tidskriftsartikel (refereegranskat)abstract
- The generation of diversity for directed protein evolution experiments shows an important bottleneck in the in vitro random mutagenesis protocols. Most Of them are biased towards specific changes that eventually confer a predicted and conservative mutational spectrum, limiting the exploration of the vast protein space. The current work describes a simple methodology to in vivo recombine mutant libraries with different nucleotide bias created by in vitro methods. This in vivo assembly was based on the accurate physiology of Saccharomyces cerevisiae, which as host, provided its high homologous recombination frequency to shuffle the libraries in a nonmutagenic way. The fungal thermophilic laccase from Myceliophthora thermophila expressed in S. cerevisiae was submitted to this protocol under the selective pressure of high concentrations of organic solvents. Mutant 2E9 with similar to 3-fold better kinetics than parent type showed two consecutive amino acid changes (G614D -GGC/GAC- and E615K -GAG/AAG-) because of the in vivo shuffling of the mutant libraries. Both mutations are located in the C-terminal tail that is specifically processed at the Golgi during the maturation of the protein by the Kex2 protease. Notoriously, the oxygen consumption at the T2/T3 trinuclear copper cluster was altered and the catalytic copper at the T1 site was perturbed showing differences in its redox potential and geometry. The change in the isoelectric point of C-terminal extension upon mutations seems to affect the folding of the protein at the posttranslational processing steps providing new insights in the significance of the C-terminal tail for the functionality of the ascomycete laccases.
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| 2. |
- Zumarraga, Miren, et al.
(författare)
-
Combinatorial saturation mutagenesis of the Myceliophthora thermophila laccase T2 mutant : the connection between the C-terminal plug and the conserved 509VSG511 tripeptide
- 2008
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Ingår i: Combinatorial chemistry & high throughput screening. - : Bentham Science Publishers Ltd.. - 1386-2073 .- 1875-5402. ; 11:10, s. 807-816
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Tidskriftsartikel (refereegranskat)abstract
- A mutant laccase from the Ascomycete Myceliophthora thermophila has been submitted to iterative cycles of combinatorial satn. mutagenesis through in vivo overlap extension in Saccharomyces cerevisiae. Over 180,000 clones were explored, among which the S510G mutant revealed a direct interaction between the conserved 509VSG511 tripeptide, located in the neighborhood of the T1 site, and the C-terminal plug. The KmO2 value of the mutant increased 1.5-fold, and the electron transfer pathway between the reducing substrate and the T1 copper ion was altered, improving the catalytic efficiency towards non-phenolic and phenolic substrates by about 3- and 8-fold. Although the geometry at the T1 site was perturbed by the mutation, paradoxically the laccase redox potential was not significantly altered. Together, the results obtained in this study suggest that the 509VSG511 tripeptide may play a hitherto unrecognized role in regulating the traffic of oxygen through the C-terminal plug, the latter blocking access to the T2/T3 copper cluster in the native enzyme.
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