Methanol, as an alternative biorefinery feedstock, has advantages of abundant sources, low price, and high degree of reduction. Therefore, it is of great socio-economic significance to develop methanol-based biological manufacturing industry. However, methanol bioconversion is limited by unfavorable kinetics of methanol oxidation and accumulation of highly toxic intermediate formaldehyde. 

Recently, a research group led by Prof. ZHENG Ping and Prof. SUN Jibin at the Tianjin Institute of Industrial Biotechnology (TIB) of the Chinese Academy of Sciences rationally designed and constructed fusion proteins of ribulose monophosphate pathway enzymes. The fusion engineering strategy enhanced methanol bioconversion to fructose 6-phosphate (F6P), an important metabolic intermediate. 

NAD-dependent methanol dehydrogenase (Mdh), 3-hexulose-6-phosphate synthase (Hps) and 6-phospho-3-hexuloisomerase (Phi) from different sources were evaluated for their catalytic activities. The candidates with the highest activity were then used to construct difunctional fusion proteins (Mdh-Hps and Hps-Phi) and trifunctional fusion proteins (Mdh-Hps-Phi) with flexible linkers.

Effects of linker length on the catalytic efficiency of fusion proteins were also investigated. The best fusion protein showed 4.8-fold improvement in methanol oxidation efficiency and 30% improvement in F6P formation efficiency.

Furthermore, dynamic light scattering and transmission electron microscope analyses suggested that fusion engineering brought changes in polymerization states of proteins, which may consequently affect the catalytic characteristics.

Their study, published in ChemBioChem, demonstrates that fusion engineering is a promising strategy for solving formaldehyde toxicity and enhancing methanol bioconversion rate. 

This work was supported by the National Natural Science Foundation of China, the Key Research Program of Chinese Academy of Sciences, the International Partnership Program of Chinese Academy of Sciences, the Special Program of Talents Development for Excellent Youth Scholars in Tianjin, and the first Special Support Plan for Talents Development and High-level Innovation and Entrepreneurship Team of the Tianjin Municipal City. 

Fusion engineering strategy for enhancing methanol bioconversion to F6P. (Image by TIB)