Use of novel selenomethionine-resistant yeast to produce selenomethionyl protein suitable for structural analysis.

Yeast is widely used to determine the tertiary structure of eukaryotic proteins, because of its ability to undergo post-translational modifications such as glycosylation. A mutant lacking S-adenosylmethionine synthesis has been reported as a suitable host for producing selenomethionine derivatives, which can help solve phase problems in protein crystallography. However, the mutant required external addition of S-adenosylmethionine for cell proliferation. Here, a selenomethionine-resistant Pichia pastoris mutant that showed S-adenosylmethionine autotrophy was isolated. Human lysozyme expressed by the mutant under the control of constitutive promoter contained selenomethionine at 65% occupancy, sufficient for use as a selenomethionine derivative for single-wavelength anomalous dispersion phasing.