Graduate School of Agriculture, Osaka Metropolitan University, 1-1 Gakuen-cho, Naka-ku, Sakai,Osaka 599-8531, Japan.
Department of Food and Nutrition, Tsu City College, 157 Ishinden-Nakano, Tsu, Mie 514-0112, Japan.
J Biochem. 2023 Jun 30;174(1):21-31. doi: 10.1093/jb/mvad016.
Lipocalin-type prostaglandin D synthase (L-PGDS) binds various hydrophobic small molecules. Since we aim to use human L-PGDS as a carrier in a drug delivery system (DDS) for poorly water-soluble drugs, quality control of the protein is indispensable. In this study, we investigated the thermodynamic stability of human L-PGDS under various pH conditions. Differential scanning calorimetry revealed that the thermal unfolding of L-PGDS was an almost-reversible two-state transition between the native and unfolded states over the pH range from 2.5 to 7.4. The linear relationship of ΔH(Tm) to Tm in this pH range gave a heat capacity change (ΔCp) of 4.76 kJ/(K·mol), which was small compared to those commonly found in globular proteins. The temperature-dependent free energy of unfolding, ΔG(T), specified by Tm, ΔH(Tm) and ΔCp, showed a pH dependence with the highest value at pH 7.4 closest to the isoelectric point of 8.3. The small value of Cp resulted in a large value of ΔG(T), which contributed to the stability of the protein. Taken together, these results demonstrated that human L-PGDS is sufficiently thermostable for storage and practical use and can be useful as a delivery vehicle of protein-based DDS.
脂氧素 A4 合酶（L-PGDS）结合各种疏水性小分子。由于我们的目标是将人 L-PGDS 用作水不溶性药物药物递送系统（DDS）的载体，因此对蛋白质进行质量控制是必不可少的。在这项研究中，我们研究了人 L-PGDS 在各种 pH 值条件下的热力学稳定性。差示扫描量热法表明，L-PGDS 的热变性是在 pH 值为 2.5 到 7.4 的范围内，从天然状态到无规卷曲状态的几乎可逆的两态转变。在该 pH 范围内，ΔH（Tm）与 Tm 的线性关系给出了 4.76 kJ/（K·mol）的热容变化（ΔCp），与通常在球状蛋白质中发现的相比很小。由 Tm、ΔH（Tm）和 ΔCp 指定的温度依赖性展开自由能，ΔG（T），在 pH 值为 7.4 时具有依赖性，最接近等电点 8.3。Cp 的小值导致 ΔG（T）的大值，这有助于蛋白质的稳定性。综上所述，这些结果表明人 L-PGDS 具有足够的热稳定性，可用于储存和实际应用，并且可以用作基于蛋白质的 DDS 的递送载体。
