The crystal structures at 2.2-A resolution of hydroxyethylene-based inhibitors bound to human immunodeficiency virus type 1 protease show that the inhibitors are present in two distinct orientations

As part of a structure-based drug design program directed against enzyme targets in the human immunodeficiency virus (HIV), we have determined the three-dimensional structures of the HIV type 1 protease complexed with two hydroxyethylene-based inhibitors. The inhibitors (SKF 107457 and SKF 108738) are hexapeptide substrate analogues with the scissile bond being replaced by a hydroxyethylene isostere. The structures were determined using x-ray diffraction data to 2.2 A measured at the Cornell High Energy Synchrotron Source on hexagonal crystals of each of the complexes. The structures have been extensively refined using a reciprocal space least-squares method to conventional crystallographic R factors of 0.186 and 0.159, respectively. The protein structure differs from that in the unliganded state of the enzyme and is most similar to that of the structure of the other reported (Jaskolski, M., Tomasselli, A. G., Sawyer, T. K., Staples, D. G., Heinrikson, R. L., Schneider, J., Kent, S. B. H., and Wlodawer, A. (1990) Biochemistry 29, 5889-5907) hydroxyethylene-based inhibitor complex. Unlike in that structure, however, the inhibitors are observed, in the present crystal structures, in two equally abundant orientations that are a consequence of the homodimeric nature of the enzyme coupled with the asymmetric structures of the inhibitors. Although the differences between the two inhibitors used in the present study are confined to the P1' site, the van der Waals interactions made by the inhibitor atoms with the amino acid residues in the protein differ throughout the structures of the inhibitors.

The three-dimensional structure of recombinant bovine chymosin at 2.3 A resolution

The crystal structure of recombinant bovine chymosin (EC 3.4.23.4; renin), which was cloned and expressed in Escherichia coli, has been determined using X-ray data extending to 2.3 A resolution. The crystals of the enzyme used in this study belong to the space group I222 with unit cell dimensions alpha = 72.7 A, b = 80.3 A, and c = 114.8 A. The structure was solved by the molecular replacement method and was refined by a restrained least-squares procedure. The crystallographic R factor is 0.165 and the deviation of bond distances from ideality is 0.020 A. The resulting model includes all 323 amino acid residues, as well as 297 water molecules. The enzyme has an irregular shape with approximate maximum dimensions of 40 x 50 x 65 A. The secondary structure consists primarily of parallel and antiparallel beta-strands with a few short alpha-helices. The enzyme can be subdivided into N- and C-terminal domains which are separated by a deep cleft containing the active aspartate residues Asp-34 and Asp-216. The amino acid residues and waters at the active site form an extensive hydrogen-bonded network which maintains the pseudo 2-fold symmetry of the entire structure. A comparison of recombinant chymosin with other acid proteinases reveals the high degree of structural similarity with other members of this family of proteins as well as the subtle differences which make chymosin unique. In particular, Tyr-77 of the flap region of chymosin does not hydrogen bond to Trp-42 but protrudes out in the P1 pocket forming hydrophobic interactions with Phe-119 and Leu-32. This may have important implications concerning the mechanism of substrate binding and substrate specificity.

A preliminary crystallographic study of recombinant human interleukin 1 beta

Recombinant human interleukin 1 beta which is expressed in Escherichia coli has been crystallized by the method of vapor diffusion using ammonium sulfate as the precipitant. The space group is P4(1) or P4(3) with a = b = 55.0 A and c = 77.1 A and one molecule in the asymmetric unit. The crystals diffract to beyond 2.4 A and are suitable for a three-dimensional x-ray structure determination.

Crystallization and preliminary x-ray diffraction studies of subtilisin GX from Bacillus sp. GX6644

Subtilisin GX, a serine protease from Bacillus species GX6644, has been crystallized by the vapor diffusion method using ammonium sulfate as the precipitant. The space group is P212121 with a = 38.4 A, b = 70.3 A, c = 73.5 A, and one molecule in the asymmetric unit. The crystals diffract to beyond 2.0-A resolution and are suitable for a high resolution three-dimensional structure determination. All x-ray data used in the preliminary crystallographic study were collected with an electronic area detector.