Abstract: S-adenosylmethionine synthetase(MAT)catalyzes the synthesis of S-adenosylmethionine(SAM)from L-methionine and ATP in all living organisms. SAM is an important biochemical molecule participating in a variety of biochemical reactions, and has attracted much interest in clinical research because of its potential to cure many diseases, such as depression, liver disease, and osteoarthritis. Accordingly, to develop a simple and effective way to enzymatically synthesize and produce SAM, the MAT gene(sam2)from Streptomyces spectabilis was expressed successfully under the control of the AOX1 promoter in the recombinant yeast Pichia pastoris KM71. Introduction of a spacer peptide(G-Spacer: NTTEEGEPK)after the α-factor, creating a G-spacer of the N-terminal extension of the MAT(GM), greatly increased the MAT spectivity activity of GM to 158% and concomitantly improved the secretion level of the GM by 92%. In contrast, the MAT activity of the recombinant GM with C-terminal His-tag(GMH)was decreased by 13% as compared to that with the GM. Conclusively, the G-Spacer seem to be of crucial importance in determining the secretion efficiency and activity of MAT in P. pastoris. The C-terminal region of the MAT might also be important to the active protein structure.

Key words: S-adenosylmethionine synthetase, Secretory expression, Pichia pastor, is, Spacer peptide, Heterologous expression