Date

2011

Author

Boy, Erdem

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Pyrococcus furiosus extracellular α-amylase is a hyperthermostable glucosyl hydrolyzing enzyme which shows unique biochemical properties that may have impact on improving starch hydrolysis process; however, it is insignificantly expressed in its native archaeal host. In this study, it was aimed to express the P. furiosus extracellular alpha-amylase (PFA) in Pichia pastoris, which is a well-recognized overexpression host used in production of heterologous proteins. In this context, first, P. furiosus was grown under anaerobic conditions in capped bottles for t= 12 h at T=90°C and then its genomic DNA was isolated. PFA coding cDNA frame was amplified using two specifically designed oligonucleotides and cloned into pPICZαA expression vector. Then wild type P. pastoris X-33 cells were transfected with pPICZαA::PFA construct. In shake flask production medium, existence of recombinant PFA activity was tested and biochemical characterization of the recombinant product was done. This was the first time PFA is expressed in an eukaryotic host. Optimum working temperature and pH of the rPFA were found to be 95 °C and within the range of 4.5-6.5, respectively. rPFA is independent to metal ions and inhibition by production medium of P. pastoris was observed, in presence of divalent metal ions. Although Saccharomyces cerevisiae α-factor secretion signal was fused to the N terminal of rPFA, minute amount of extracellular secretion was detected but the majority of the enzymatic activity remained in the intracellular medium. The best producer strain was selected by measuring α-amylase activity in cell extracts by DNS method. Effects of pH on cell growth and recombinant protein production were determined by shake flask experiments and maximum of 4800 U/l rPFA was detected with 7.30 g/l wet cell density in pH=6 buffered medium. In order to achieve higher rPFA production, two bioreactor experiments were designed at two different pH operation conditions, namely pH=4 and pH=5, in a working volume of 1 L. The dissolved oxygen tension was kept over 20% and predetermined exponential methanol feeding strategy was employed in order to fix specific cell growth rate, µ, at 0.03 h-1. At pH=4 operation, maximum of 73,400 U/l α-amylase activity was detected at the t=27 h of production phase when the wet cell density was 209 g/l.

Subject Keywords

Biotechnology.

URI

http://etd.lib.metu.edu.tr/upload/12613922/index.pdf
https://hdl.handle.net/11511/20793

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Graduate School of Natural and Applied Sciences, Thesis