Blocking S-adenosylmethionine synthesis in yeast allows selenomethionine incorporation and multiwavelength anomalous dispersion phasing.

Saccharomyces cerevisiae is an ideal host from which to obtain high levels of posttranslationally modified eukaryotic proteins for x-ray crystallography. However, extensive replacement of methionine by selenomethionine for anomalous dispersion phasing has proven intractable in yeast. We report a general method to incorporate selenomethionine into proteins expressed in yeast based ...
on manipulation of the appropriate metabolic pathways. sam1(-) sam2(-) mutants, in which the conversion of methionine to S-adenosylmethionine is blocked, exhibit reduced selenomethionine toxicity compared with wild-type yeast, increased production of protein during growth in selenomethionine, and efficient replacement of methionine by selenomethionine, based on quantitative mass spectrometry and x-ray crystallography. The structure of yeast tryptophanyl-tRNA synthetase was solved to 1.8 A by using multiwavelength anomalous dispersion phasing with protein that was expressed and purified from the sam1(-) sam2(-) strain grown in selenomethionine. Six of eight selenium residues were located in the structure.
Mesh Terms:
Crystallography, X-Ray, S-Adenosylmethionine, Saccharomyces cerevisiae, Selenomethionine, Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
Proc. Natl. Acad. Sci. U.S.A.
Date: Apr. 17, 2007
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