Hu X, Rodgers K R, Mukerji I, Spiro T G
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
Biochemistry. 1999 Mar 23;38(12):3462-7. doi: 10.1021/bi982513c.
On the basis of static and time-resolved resonance Raman spectroscopy of HbA and of a mutant, HbK (Dalpha99N), a specific reaction coordinate is proposed for the allosteric transition in human hemoglobin. The heme is held between proximal (F) and distal (E) helices, whose orientation is responsive to forces generated by ligation and deligation. The E and F helices are in turn tethered via H-bonds to the A and H helices. These outer helices follow the E-F motion, thereby repositioning the N- and C-termini, which form the intersubunit salt bridges in the T quaternary structure. When the T state interface is weakened by Asp --> Asn substitution at a quaternary H-bond (HbK), the Fe-His bond is relaxed and becomes responsive to allosteric effectors. The same E-F motion is observed in HbK, but the A-H following motion is delayed, relative to HbA, as is the Asn H-bond formation.
基于成人血红蛋白A（HbA）及其突变体HbK（Dα99N）的静态和时间分辨共振拉曼光谱，提出了人类血红蛋白变构转变的特定反应坐标。血红素位于近端（F）和远端（E）螺旋之间，其取向对由配体结合和去结合产生的力有响应。E螺旋和F螺旋又通过氢键与A螺旋和H螺旋相连。这些外部螺旋跟随E-F运动，从而重新定位N端和C端，它们在T四级结构中形成亚基间盐桥。当在四级氢键处由天冬氨酸（Asp）替换为天冬酰胺（Asn）（HbK）而削弱T态界面时，铁-组氨酸键松弛并变得对变构效应剂有响应。在HbK中观察到相同的E-F运动，但相对于HbA，随后的A-H运动延迟，天冬酰胺氢键形成也延迟。
