thermomethanolica BCC16875 was relatively lower than that reported from P. pastoris (Promdonkoy et al., 2009). This is unlikely to be due to proteolytic degradation of the recombinant protein produced from the new yeast strain because
extracellular protease activity was not detected (data not shown). Intriguingly, rPHY expressed from the two promoters showed different mobility patterns in SDS-PAGE. rPHY produced from AOX1 showed a major molecular mass (MW) of c. 66 kDa, although a small variation of sizes still occurred. On the other hand, rPHY produced from the GAP promoter showed a higher and more heterogeneous MW (Fig. 1a). After PNGaseF digestion to eliminate the N-linked glycan moiety, rPHY expressed in P. thermomethanolica
BCC16875 from the two different expression conditions exhibited the same SDS-PAGE mobility of 51 kDa (Fig. 1b). We infer from this result that N-linked oligosaccharides were learn more assembled on rPHY to different extents depending on the expression promoter used. The efficiency of P. thermomethanolica BCC16875 for producing heterologous proteins was also tested for expression of xylanase, a fungal non-glycosylated protein. It was found that xylanase was efficiently produced as secreted protein with similar mobility in SDS-PAGE to that produced in P. pastoris (Ruanglek et al., 2007). The levels of constitutive expression of phytase and xylanase from both P. thermomethanolica BCC16875 and P. pastoris KM71 were comparable (0.2–0.5 mg mL−1). From the phytase amino acid sequence, eight potential find more N-glycosylation sites were predicted (Promdonkoy et al., 2009). Glycosylation patterns of rPHY produced from both promoters were analyzed and compared.
rPHY glycosylation mainly consisted of Man8GlcNAc2 to Man12GlcNAc2, as shown in peaks detected at 20–30 min retention time. However, for constitutively expressed rPHY, larger sized N-glycan fractions (> Man15GlcNAc2) were observed after 30 min, consistent with high molecular weight glycosylated rPHY expressed from the GAP promoter as detected by SDS-PAGE (Fig. 2a and b). The N-glycans from both rPHY were then digested with α-1,2-mannosidase. Large oligosaccharide structures were partially converted to Man5GlcNAc and Man6GlcNAc, suggesting that click here the outer chain oligosaccharides contained α-1,2 mannose linkages (data not shown). Digestion with jack bean mannosidase converted most of N-glycans produced from GAP to Man1GlcNAc2, although small fractions of Man4-7 and larger N-glycans remained (Fig. 2c). After digesting with β-mannosidase, the peak corresponding to Man1GlcNAc2 was converted to give a peak corresponding to GlcNAc, indicating the presence of 1,4-β-linked core oligosaccharides, as found in all eukaryotes. No further conversion of other remaining N-glycans was observed, suggesting that no additional β-inkage was present in the oligosaccharides (Fig. 2c).