No abstract

The x-ray crystal structure of recombinant human interferon-gamma has been determined with the use of multiple-isomorphous-replacement techniques. Interferon-gamma, which is dimeric in solution, crystallizes with two dimers related by a noncrystallographic twofold axis in the asymmetric unit. The protein is primarily alpha helical, with six helices in each subunit that comprise approximately 62 percent of the structure; there is no beta sheet. The dimeric structure of human interferon-gamma is stabilized by the intertwining of helices across the subunit interface with multiple intersubunit interactions.

The program RIBBONS 2.0 allows real‐time viewing of solid shaded ribbon models of macromolecules. The primary features of the software are the ability to create a wide variety of styles of ribbon drawings interactively and to toggle between various coloring schemes chosen to reflect assorted geometrical and biochemical properties. Spheres, cylinders, dots, polygons and text are also supported. The auxiliary programs included make RIBBONS 2.0 a powerful tool for visual structural analysis as well as for presentation graphics. The program is currently available only for the Silicon Graphics 4D series of workstations. A port to the Evans & Sutherland ESV workstation employing PEX is under development.

No abstract

We report here the crystal structure of the minimal ligand-binding segment of the Staphylococcus aureus MSCRAMM, clumping factor A. This ®brinogen-binding segment contains two similarly folded domains. The fold observed is a new variant of the immunoglobulin motif that we have called DE-variant or the DEv-IgG fold. This subgroup includes the ligand-binding domain of the collagen-binding S.aureus MSCRAMM CNA, and many other structures previously classi®ed as jelly rolls. Structure predictions suggest that the four ®brinogen-binding S.aureus MSCRAMMs identi®ed so far would also contain the same DEv-IgG fold. A systematic docking search using the C-terminal region of the ®brinogen g-chain as a probe suggested that a hydrophobic pocket formed between the two DEv-IgG domains of the clumping factor as the ligand-binding site. Mutagenic substitution of residues Tyr256, Pro336, Tyr338 and Lys389 in the clumping factor, which are proposed to contact the terminal residues 408 AGDV 411 of the g-chain, resulted in proteins with no or markedly reduced af®nity for ®brinogen.

Crystallographers are increasingly determining structures of protein constructs that include His tags. Many have taken for granted that these tags have little effect on the native structure. This paper surveys and compares crystal structures with and without His tags. It is observed that actual refined tag residues fitted into density occur in less that 10% of the tagged sequences. However, higher resolution crystals are observed when this occurs. It is shown that these purification tags generally have no significant effect on the structure of the native protein. Resolution and R factors are not affected, but the overall B factors are slightly higher. Additional annotation in the PDB format to make tag definition explicit is suggested.

No abstract

The crystal structure of the recombinant 19,000 M(r) binding domain from the Staphylococcus aureus collagen adhesin has been determined at 2 A resolution. The domain fold is a jelly-roll, composed of two antiparallel beta-sheets and two short alpha-helices. Triple-helical collagen model probes were used in a systematic docking search to identify the collagen-binding site. A groove on beta-sheet I exhibited the best surface complementarity to the collagen probes. This site partially overlaps with the peptide sequence previously shown to be critical for collagen binding. Recombinant proteins containing single amino acid mutations designed to disrupt the surface of the putative binding site exhibited significantly lower affinities for collagen. Here we present a structural perspective for the mode of collagen binding by a bacterial surface protein.