Role of side-chains in the cooperative β-hairpin folding of the short C-terminal fragment derived from streptococcal protein G
Role of side-chains in the cooperative β-hairpin folding of the short C-terminal fragment derived from streptococcal protein G
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DOI：
10.1021/bi000013p
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发表时间：
2000-05-30
期刊：
影响因子：
2.9
通讯作者：
Munekata, E
中科院分区：
文献类型：
--
作者：
Kobayashi, N;Honda, S;Munekata, E
已知链球菌蛋白G免疫球蛋白结合域的短c端片段在生理条件下形成天然的β -发夹。为了了解短肽的协同折叠，通过分析核磁共振信号的温度依赖性，研究了该片段的8个ala取代突变体的结构稳定性。通过比较得到的热力学参数，我们发现非极性残基Tyr45和Phe52以及极性残基Asp46和Thr49对β -发夹折叠至关重要。结果表明，非极性侧链之间有很强的相互作用，参与了假定的疏水簇，而极性侧链在环周围形成了相当刚性的构象（46-51）。我们还研究了n端片段突变体在不同温度下的复合物形成，以获得它们的热展开曲线，发现残基Asp36和Thr39的突变极大地破坏了复合物的稳定性，而Asp47的取代则略微稳定了复合物。从这些结果中，我们推断疏水簇的形成和环的刚性（46-51）共同稳定了片段的β -发夹结构。这些相互作用形成了稳定的β发夹，可能是整个结构域早期折叠事件中重要的初始结构支架。
A Short C-terminal fragment of immunoglobulin-binding domain of stroptococcal protein G is known to form nativelike beta-hairpin at physiological conditions. To understand the cooperative folding of the short peptide, eight Ala-substituted mutants of the fragment were investigated with respect to their structural stabilities by analyzing temperature dependence of NMR signals. On comparison of the obtained thermodynamic parameters, we found that the nonpolar residues Tyr45 and Phe52 and the polar residues Asp46 and Thr49 are crucial for the beta-hairpin folding. The results suggest a strong interaction between the nonpolar side chains that participates in a putative hydrophobic cluster and that the polar side chains form a fairly rigid conformation around the loop (46-51). We also investigated the complex formation of the mutants with N-terminal fragment at the variety of temperature to get their thermal unfolding profiles and found that the mutations on the residues Asp36 and Thr39 largely destabilized the complexes, while substitution of Asp47 slightly stabilized the complex. From these results, we deduced that both the hydrophobic cluster formation and the rigidity of the loop (46-51) cooperatively stabilize the beta-hairpin structure of the fragment. These interactions which form a stable beta-hairpin may be the initial structural scaffold which is important in the early folding events of the whole domain.