Three‐dimensional structure of fungal proteinase K reveals similarity to bacterial subtilisin

The three‐dimensional structure of the fungal serine protease proteinase K has been determined at 3.3 A resolution by single crystal X‐ray diffraction analysis. The enzyme crystallizes in the tetragonal space group P4(3)2(1)2 with cell constants a = b = 68.3 A, c = 108.5 A. The asymmetric unit consists of one monomer of 27 000 daltons mol. wt., approximately 50% higher than the so far assumed value of 18 500 daltons. The main chain fold of proteinase K shows a high degree of tertiary homology with the corresponding bacterial subtilisin BPN’. Proteinase K is the second enzyme in this family of serine proteases to be studied by X‐ray diffraction, thus confirming the existence of two unrelated families of serine proteases in pro‐and eukaryotes.