Mayr E M, Jaenicke R, Glockshuber R
Institut für Biophysik und Physikalische Biochemie, Universität Regensburg, Germany.
J Mol Biol. 1997 Jun 6;269(2):260-9. doi: 10.1006/jmbi.1997.1033.
gammaB-crystallin from vertebrate eye lens is an all beta-sheet two-domain protein with a high degree of intrachain symmetry. Its N and C-terminal domains show high levels of sequence similarity and structural identity. In natural gammaB-crystallin, the domains fold independently. The recombinantly expressed isolated domains are stable monomeric proteins, which do not associate spontaneously to form a gammaB-like dimer. In contrast to their identical folding topology, the two domains obviously follow different folding mechanisms. While the two-state model is valid for the C-terminal domain, the folding behaviour of the N-terminal domain is more complex. The stability of the C-terminal domain is strongly dependent on pH. At pH 2, the C-terminal domain in its isolated form is significantly less stable than within the gammaB-molecule. In contrast, the isolated N-terminal domain does not differ in its stability from the N-terminal domain in wild-type gammaB-crystallin. The strongly decreased stability of the C-terminal domain at acid pH allowed a dissection of the intrinsic stabilities of the domains and their interactions in gammaB-crystallin. At pH 2, domain interactions contribute -16 kJ/mol to the overall stability of gammaB-crystallin.
脊椎动物眼晶状体中的γB-晶状体蛋白是一种全β折叠的双结构域蛋白，具有高度的链内对称性。其N端和C端结构域显示出高度的序列相似性和结构一致性。在天然γB-晶状体蛋白中，这些结构域独立折叠。重组表达的分离结构域是稳定的单体蛋白，不会自发缔合形成γB样二聚体。与其相同的折叠拓扑结构相反，这两个结构域显然遵循不同的折叠机制。虽然两态模型适用于C端结构域，但N端结构域的折叠行为更为复杂。C端结构域的稳定性强烈依赖于pH值。在pH 2时，分离形式的C端结构域比在γB分子内的稳定性明显更低。相比之下，分离的N端结构域与野生型γB-晶状体蛋白中的N端结构域在稳定性上没有差异。酸性pH下C端结构域稳定性的大幅下降使得能够剖析γB-晶状体蛋白中各结构域的内在稳定性及其相互作用。在pH 2时，结构域间相互作用对γB-晶状体蛋白的整体稳定性贡献为-16 kJ/mol。
