Influence of a family 29 carbohydrate binding module on the recombinant production of galactose oxidase in Pichia pastoris

Herein, we report the extracellular expression of carbohydrate active fusion enzymes in Pichia pastoris. Particularly, CBM29-1-2 from Piromyces equi was separately fused to the N- and C-terminus of galactose 6-oxidase (GaO, D-galactose: oxygen 6-oxidoreductase, EC 1.1.13.9, CAZy family AA5) from Fusarium graminearum, generating CBM29-GaO and GaO-CBM29, respectively. P. pastoris was transformed with expression vectors encoding GaO, CBM29-GaO and GaO-CBM29, and the fusion proteins were expressed in both shake-flask and 2L bioreactor systems. Volumetric production yields and specific GaO activity increased when expression was performed in a bioreactor system compared to shake-flask cultivation. This was observed for both CBM29-GaO and GaO-CBM29, and is consistent with previous reports of GaO expression in P. pastoris (Spadiut et al., 2010; Anasontzis et al., 2014) [1,2]. Fusion of CBM29 to the C-terminal of GaO (GaO-CBM29) resulted in a stable uniform protein at the expected calculated size (107 kDa) when analyzed with SDS-PAGE. By comparison, the expression of the N-terminal fusion protein (CBM29-GaO) was low, and two truncated versions of CBM29-GaO were coexpressed with the full-sized protein. Despite differences in protein yield, the specific GaO activity on galactose was not affected by CBM29 fusion to either the N- or C-terminus of the enzyme. A detailed description of the catalytic and physiochemical properties of CBM29-GaO and GaO-CBM29 is available in the parent publication (Mollerup et al., 2015) [3].