A simplified amplified-fragment length polymorphism (AFLP) method was used to genotype Pichia pastoris strains obtained by transformation of P. pastoris strain GS115 with a single integration vector. A total of 14 transformants and 3 control strains were analyzed, which generated 16 different band patterns. A clonal variation was obtained after the transformation process due to genetic differences generated during the transformation event of the host strain. Furthermore, the cluster analysis showed that the transformants with lesser genetic differences with respect to the P. pastoris host strain are the recombinant strains with the highest level of recombinant protein production.
A simple protocol for easy PCR screening of P. pastoris transformants is described. In short, the P. pastoris cells are lysed with very small amount of the enzyme Zymolase and the crude cell lysate is directly used in PCR. This protocol needs no tube transfer steps and also obliviates the requirement of freezing the samples at -80°C before PCR screening. Because of a single step screenig, both overall and actual hands on time are considerably reduced.
Cyclic AMP dependent protein kinase (PKA) from Pichia pastoris yeast cells was found to be activated by either cAMP or cGMP. Analogs of cAMP such as 8-chloro-cAMP and 8-bromo-cAMP were as potent as cAMP in PKA activation while N6, 2'- O-dibutyryl-cAMP did not stimulate the enzyme activity. It was shown that protamine sulfate was almost equally phosphorylated in the presence of 1-2 X 10-6 M cAMP or cGMP while other substrates such as Kemptide, ribosomal protein S6 were phosphorylated to a lower extent in the presence of cGMP. It was demonstrated that pyruvate kinase is a substrate of PKA which co-purified with the P. pastoris enzyme. Moreover, pyruvate kinase was phosphorylated by PKA in the presence of cAMP and cGMP to comparable levels.
Pichia pastoris secretes few native proteins. However, the more than 1 g 1-1 of extracellularly expressed mannan interfered with the purification of our extracellularly expressed, non-glycosylated recombinant protein. Concanavalin A-agarose removed more than 95% of the unwanted mannan as monitored by phenol reaction. A 13C-based NMR assay confirmed this improvement. Concanavalin A-agarose can assist the purification of extracellular expressed, non-glycosylated proteins from yeasts.
Cry4Aa 678 amino acids fragment (60 kDa) was cloned into Escherichia coli. After induction with IPTG the 60 kDa Cry4Aa fragment was purified by Ni chromatography, separated by SDS PAGE and identified by mass spectrometry (MS/MS). The 60 kDa Cry4Aa fragment exhibited high toxicity towards Ae. aegypti larvae. The earlier results [1] show that Pichia pastoris yeast cells expressing tmfA (synthetic gene coding for the Trypsin Modulating Oostatic Factor of Ae. aegypti) together with E. coli cells expressing Bti toxin genes (cry4Aa, cry11Aa, cyt1Aa and p20) are synergistic. Therefore, P. pastoris, which synthesizes high amounts of heterologous proteins was genetically engineered to produce TMOF and Cry4Aa. Codon-optimized synthetic genes, cry4Aa-tmfA, gst-cry4Aa-tmfA, tmfA and gfptmfA that were expressed by P. pastoris and fed to Ae. aegypti larvae caused 90% mortality. GST (glutathione-S-transferase) enhanced the activity of Cry4Aa-TMOF and protected it from heat denaturation and GFP (Green Fluorescent Protein)- TMOF allowed us to follow yeast cells consumption by individual larva using fluorescent microscopy. This report shows for the first time that 60 kDa Cry4Aa and TMOF expressed together in P. pastoris are highly toxic to Ae. aegypti larvae.
It was found that wild type yeast Pichia pastoris can tolerate vanadate concentration as high as 25 mM in the growth medium. Moreover, four vanadate-resistant P. pastoris strains designated JC100/1, JC100/3, JC100/9 and JC100/15 exhibiting tolerance up to 150 mM vanadate were selected. Growth of P. pastoris was correlated with vanadate to vanadyl reduction and its accumulation in the growth medium. In two selected strains, JC100/9 and JC100/15, protein kinase A activity was much higher in comparison to the wild type strain even without vanadate addition to the growth medium. Moreover, in the presence of vanadate, protein kinase A activity was significantly increased in the wild type and the vanadate-resistant JC100/1 and JC100/3 strains. It was also found that phosphorylation of a 40 kDa protein associated with ribosomes occured in all vanadate-resistant strains from the logarithmic, while in the wild type strain from the stationary growth phase. From the presented results it can be concluded that a protein kinase A signalling pathway(s) might be involved in the mechanism of P. pastoris vanadate resistance. The results also indicate a possible role of the 40 kDa protein in protection of P. pastoris against vanadate toxicity.