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外文期刊>The biochemical journal
>Structural stabilization of protein 4.1R FERM domain upon binding to apo-calmodulin: novel insights into the biological significance of the calcium-independent binding of calmodulin to protein 4.1R
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Structural stabilization of protein 4.1R FERM domain upon binding to apo-calmodulin: novel insights into the biological significance of the calcium-independent binding of calmodulin to protein 4.1R
pIn erythrocytes, 4.1Rsup80/sup (80 kDa isoform of protein 4.1R) binds to the cytoplasmic tail of the transmembrane proteins band 3 and GPC (glycophorin C), and to the membrane-associated protein p55 through the N- (N-terminal), α- (α-helix-rich) and C- (C-terminal) lobes of R30 [N-terminal 30 kDa FERM (4.1/ezrin/radixin/moesin) domain of protein 4.1R] respectively. We have shown previously that R30 binds to CaM (calmodulin) in a Casup2+/sup-independent manner, the equilibrium dissociation constant (iK/isubd/sub) for R30–CaM binding being very similar (in the submicromolar range) in the presence or absence of Casup2+/sup. In the present study, we investigated the consequences of CaM binding on R309s structural stability using resonant mirror detection and FTIR (Fourier-transform IR) spectroscopy. After a 30 min incubation above 40°C, R30 could no longer bind to band 3 or to GPC. In contrast, R30 binding to p55, which could be detected at a temperature as low as 34°C, was maintained up to 44°C in the presence of apo-CaM. Dynamic light scattering measurements indicated that R30, either alone or complexed with apo-CaM, did not aggregate up to 40°C. FTIR spectroscopy revealed that the dramatic variations in the structure of the β-sheet structure of R30 observed at various temperatures were minimized in the presence of apo-CaM. On the basis of iK/isubd/sub values calculated at various temperatures, ΔiC/isubp/sub and ΔiG/i° for R30 binding to apo-CaM were determined as ?10 kJ·Ksup?1/sup·molsup?1/sup and ~?38 kJ·molsup?1/sup at 37°C (310.15 K) respectively. These data support the notion that apo-CaM stabilizes R30 through interaction with its β-strand-rich C-lobe and provide a novel function for CaM, i.e. structural stabilization of 4.1Rsup80/sup./p
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机译：>在红细胞中，4.1R 80 （4.1R的80kDa亚型）与跨膜蛋白条带3和GPC（糖蛋白C）的胞质尾结合，并与膜相关蛋白p55通过R30 [N-末端30kDa FERM（4.1 / ezrin / radixin / moesin）结构域的N-（N-末端），α-（富含α-螺旋）和C-（C-末端）叶蛋白质4.1R]。先前我们已经证明，R30以Ca 2 + 独立的方式与CaM（钙调蛋白）结合，即平衡解离常数（ K d ）在存在或不存在Ca 2 + 时，R30–CaM的结合非常相似（在亚微摩尔范围内）。在本研究中，我们使用共振镜检测和FTIR（傅里叶变换红外）光谱研究了CaM结合对R309s结构稳定性的影响。在40°C以上温育30分钟后，R30不再与3带或GPC结合。相反，在存在apo-CaM的情况下，R30与p55的结合（可在低至34°C的温度下检测到）保持在44°C。动态光散射测量表明，R30单独或与apo-CaM复合时，在最高40°C时不会聚集。 FTIR光谱显示，在存在脱辅基CaM的情况下，在各种温度下观察到的R30的β-折叠结构的剧烈变化都被最小化。根据在各种温度下计算的 K d 值，Δ C p 和Δ G < R 30与载脂蛋白CaM结合的/ i>°确定为？10 kJ·K ？1 ·mol ？1 和〜？38 kJ·mol α。 1 分别在37°C（310.15 K）下。这些数据支持apo-CaM通过与其富含β链的C瓣相互作用来稳定R30的观点，并为CaM提供了一种新颖的功能，即4.1R 80 的结构稳定。
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