Eck M J, Beutler B, Kuo G, Merryweather J P, Sprang S R
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235-9050.
J Biol Chem. 1988 Sep 15;263(26):12816-9.
Crystals of tumor necrosis factor (TNF) have been obtained in two forms. Rhombohedral crystals grow in 1.8 to 2.0 M ammonium sulfite, pH 7.8 at 21 degrees C, and tetragonal crystals grow in 2.6 M magnesium sulfate, pH 5.5 at 25 degrees C. Analysis of TNF by isoelectric focusing under native and denaturing conditions indicates that TNF molecules exist as trimers in solution. The rhombohedral cachectin crystals belong to space group R3 and have unit cell constants a = b = c = 47.65 A and alpha = beta = gamma = 88.1 degrees. Density determinations and the space group indicate that the unit cell contains one 51,000-dalton trimer. These crystals are stable in the x-ray beam and diffract to at least 1.85 A but are apparently twinned by merohedry. The tetragonal crystals are space group P4(3)2(1)2 or its enantiomorph P4(1)2(1)2 and have unit cell constants a = b = 95.08, c = 117.49. The asymmetric unit contains one trimer; the crystals are stable in the x-ray beam and diffract to beyond 3 A.
肿瘤坏死因子（TNF）晶体有两种形式。菱面体晶体在1.8至2.0M亚硫酸铵、pH7.8、21℃条件下生长，四方晶体在2.6M硫酸镁、pH5.5、25℃条件下生长。在天然和变性条件下通过等电聚焦对TNF进行分析表明，TNF分子在溶液中以三聚体形式存在。菱面体恶病质素晶体属于空间群R3，晶胞常数a = b = c = 47.65 Å，α = β = γ = 88.1°。密度测定和空间群表明晶胞包含一个51,000道尔顿的三聚体。这些晶体在X射线束中稳定，衍射至至少1.85 Å，但显然存在孪晶现象。四方晶体属于空间群P4(3)2(1)2或其对映体P4(1)2(1)2，晶胞常数a = b = 95.08，c = 117.49。不对称单元包含一个三聚体；晶体在X射线束中稳定，衍射至3 Å以上。
