STRUCTURE OF A NEW ALKALINE SERINE-PROTEASE (M-PROTEASE) FROM BACILLUS SP KSM-K16

An alkaline serine protease, M-protease, from Bacillus sp, KSM-K16 has been crystallized. Two morphologically different crystal forms were obtained. Crystal data of form 1: space group P2(1)2(1)2(1), a = 47.3, b = 62.5, c = 75.6 Angstrom, V = 2.23 x 10(5) Angstrom(3), Z = 4 and V-m = 2.09 Angstrom(3) Da(-1). Crystal data of form 2: space group P2(1)2(1)2(1), a = 75.82(2), b = 57.79(2), c = 54.19(1)Angstrom, V = 2.29(2) x 10(5) Angstrom(3) Z = 4 and V-m = 2.15 Angstrom(3) Da(-1). The crystal structure df M-protease in form 2 has been solved by molecular replacement using the atomic model of subtilisin Carlsberg (SEC) which is 60% homologous with M-protease, and refined to the crystallographic R factor of 0.189 for 7004 reflections with F-o/sigma(F) > 3 between 7 and 2.4 Angstrom resolution. The final model of M-protease contains 1882 protein atoms, two calcium ions and 44 water molecules. The three-dimensional structure of M-protease is essentially similar to other subtilisins of known structure. The 269 C-alpha positions of M-protease have an r.m.s, difference of 1.06 Angstrom with the corresponding positions of SBC. The crystal data of form 2 are close to those of SBC, though the structure determination of form 2 made it clear that it is not isomorphous to the crystal structure of SBC. The deletions of amino acids occur at the residues 36' and 160'-163' compared with SBC (numerals with primes show the numbering for SBC). The deletion of the four residues (160'-163') may significantly affect the lack of isomorphism between M-protease and SBC.