Department of Biochemistry, Aligarh Muslim University, Aligarh, Uttar Pradesh, India.
Biopolymers. 2010 Aug;93(8):708-17. doi: 10.1002/bip.21451.
Thiol proteinase inhibitors are crucial to proper functioning of all living tissues consequent to their cathepsin regulatory and myriad important biologic properties. Equilibrium denaturation of dimeric goat pancreas thiol proteinase inhibitor (PTPI), a cystatin superfamily variant has been studied by monitoring changes in the protein's spectroscopic and functional characteristics. Denaturation of PTPI in guanidine hydrochloride and urea resulted in altered intrinsic fluorescence emission spectrum, diminished negative circular dichroism, and loss of its papain inhibitory potential. Native like spectroscopic properties and inhibitory activity are only partially restored when denaturant is diluted from guanidine hydrochloride unfolded samples demonstrating that process is partially reversible. Coincidence of transition curves and dependence of transition midpoint (3.2M) on protein concentration in guanidine hydrochloride-induced denaturation are consistent with a two-state model involving a native like dimer and denatured monomer. On the contrary, urea-induced unfolding of PTPI is a multiphasic process with indiscernible intermediates. The studies demonstrate that functional conformation and stability are governed by both ionic and hydrophobic interactions.
硫醇蛋白酶抑制剂对所有活组织的正常功能都至关重要，这是由于它们对组织蛋白酶的调节作用和众多重要的生物学特性。通过监测蛋白质光谱和功能特性的变化，研究了二聚体山羊胰腺硫醇蛋白酶抑制剂（PTPI），即半胱氨酸蛋白酶抑制剂超家族变体的平衡变性。盐酸胍和脲导致 PTPI 的变性会改变其内在荧光发射光谱，降低负圆二色性，并丧失其木瓜蛋白酶抑制潜力。当从盐酸胍展开的样品中稀释变性剂时，只有部分恢复了类似天然的光谱特性和抑制活性，这表明该过程部分是可逆的。在盐酸胍诱导的变性中，转变曲线的重合和转变中点（3.2M）对蛋白质浓度的依赖性与涉及类似天然的二聚体和变性单体的两态模型一致。相反，PTPI 被脲诱导的展开是一个多相过程，其中没有可识别的中间体。这些研究表明，功能构象和稳定性受离子和疏水相互作用的控制。
