Lin S L, Stern E A, Kalb A J, Zhang Y
Department of Physics, University of Washington, Seattle 98195.
Biochemistry. 1991 Mar 5;30(9):2323-32. doi: 10.1021/bi00223a006.
We report details on measurements by the X-ray absorption fine structure (XAFS) technique of the conformational changes around the transition metal binding site (S1) of the protein concanavalin A induced by crystallization when that site is occupied by Zn. A change from hexa- to tetracoordination occurs at the S1 site on crystallization when the calcium-binding site (S2) is occupied by a calcium atom. When the S2 site is unoccupied, the Zn is pentacoordinated both in solution and in the crystal. The average distance to the coordination shell increases with coordination number as expected. Conformational changes are detected up to 4.5 A from the Zn, the limit of sensitivity of the XAFS technique. When the Zn is hexacoordinated, the ligands around the Zn, as determined by XAFS, are consistent with the crystal structure determination results of five oxygens and one nitrogen. The atom that is released in the tetracoordinated Zn. decreases to five is an oxygen atom, and, in addition, the nitrogen is released in the tetracoordinated Zn. Thus, when S2 is emptied, the protein gains a ligand about the Zn site in the crystal and loses one in solution. These results provide direct evidence that the protein conformation can be altered by the intermolecular forces of crystallization.
我们报告了有关通过X射线吸收精细结构（XAFS）技术测量的详细信息，该测量针对的是当伴刀豆球蛋白A的过渡金属结合位点（S1）被锌占据时，由结晶诱导的该蛋白围绕该位点的构象变化。当钙结合位点（S2）被一个钙原子占据时，在结晶过程中S1位点会发生从六配位到四配位的变化。当S2位点未被占据时，锌在溶液和晶体中均为五配位。到配位层的平均距离如预期的那样随着配位数的增加而增大。在距锌4.5埃处检测到构象变化，这是XAFS技术的灵敏度极限。当锌为六配位时，通过XAFS确定的锌周围的配体与五个氧原子和一个氮原子的晶体结构测定结果一致。在四配位锌中减少到五个的释放原子是一个氧原子，此外，在四配位锌中氮也会释放。因此，当S2为空时，该蛋白在晶体中锌位点周围获得一个配体，而在溶液中失去一个配体。这些结果提供了直接证据，证明蛋白质构象可被结晶的分子间力改变。
