Philo John S, Yang Tzung-Horng, LaBarre Michael
Alliance Protein Laboratories, 3957 Corte Cancion, Thousand Oaks, CA 91360, USA.
Biophys Chem. 2004 Mar 1;108(1-3):77-87. doi: 10.1016/j.bpc.2003.10.010.
The state of oligomerization of macrophage migration inhibitory factor (MIF, also known as glycosylation inhibiting factor, GIF) in solution has been variously reported as monomer, dimer, trimer, or mixtures of all three. Several crystal structures show MIF to be a trimer. Sedimentation velocity shows a recombinant human MIF sample is quite homogeneous, with 98% as a species with s(20,w)=3.07 S and D(20,w)=8.29 x 10(-7) cm(2)/s. Using the partial specific volume calculated from the amino acid composition these values imply a mass of 33.56 kDa, well above that of dimer, but also 9% below the trimer mass of 37.035 kDa. Sedimentation equilibrium data at loading concentrations from 0.01 to 1 mg/ml show unequivocally that the self-association is extremely tight. However, the apparent mass is 33.53 kDa [95% confidence 33.25-33.82], again 9% below that expected for 100% trimer. To examine the possibility this protein has an unusual partial specific volume, sedimentation equilibrium was also done in H(2)O/D(2)O mixtures, giving 0.765+/-0.017 ml/g rather than the calculated 0.735 ml/g. With this revised partial specific volume, the equilibrium and velocity data each give M=37.9+/-2.8 kDa, fully consistent with a strongly-associated trimeric quaternary structure.
巨噬细胞迁移抑制因子（MIF，也称为糖基化抑制因子，GIF）在溶液中的寡聚化状态有多种报道，分别为单体、二聚体、三聚体或这三种形式的混合物。几个晶体结构显示MIF为三聚体。沉降速度表明重组人MIF样品相当均一，98%为s(20,w)=3.07 S和D(20,w)=8.29×10(-7) cm(2)/s的一种形式。根据氨基酸组成计算出的偏比容，这些值意味着质量为33.56 kDa，远高于二聚体的质量，但也比三聚体质量37.035 kDa低9%。在0.01至1 mg/ml的加载浓度下的沉降平衡数据明确显示自缔合非常紧密。然而，表观质量为33.53 kDa [95%置信区间为33.25 - 33.82]，同样比100%三聚体预期的质量低9%。为了研究这种蛋白质是否具有异常的偏比容，还在H(2)O/D(2)O混合物中进行了沉降平衡实验，得到的结果是0.765±0.017 ml/g，而不是计算出的0.735 ml/g。采用这个修正后的偏比容，平衡和速度数据各自给出M = 37.9±2.8 kDa，与强缔合的三聚体四级结构完全一致。
