Selenomethionine labeling of recombinant proteins

Selenomethionine incorporation is a standard method for determining the phases in protein crystallography by single- or multiwavelength anomalous dispersion. Recombinant expression of selenomethionine-containing protein in non-auxotrophic Pichia pastoris strains yield an incorporation of about 50%. The expression of a mutated variant of Penicillium minioluteum dextranase in P. pastoris is used to illustrate the method utilized to obtain selenomethionyl-substituted protein and to show the phasing power of the acquired anomalous signal. The dextranase structure was solved using the anomalous signal achieved from 50% selenomethionine incorporation.