A thermally induced phase transition in a viral capsid transforms the hexamers, leaving the pentamers unchanged
A thermally induced phase transition in a viral capsid transforms the hexamers, leaving the pentamers unchanged
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DOI：
10.1016/j.jsb.2006.11.006
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发表时间：
2007-05-01
影响因子：
3
通讯作者：
Steven, Alasdair C.
中科院分区：
文献类型：
--
作者：
Conway, James F.;Cheng, Naiqian;Steven, Alasdair C.
扫描量热法结合低温电子显微镜提供了一个强有力的方法来研究多蛋白质复合物中的层次相互作用。量热法可以检测某些相互作用被破坏的温度，冷冻电镜可以揭示伴随的结构变化。噬菌体HK 97的前衣壳（Prohead 1）是一个直径450埃的外壳，由60个gp 5六聚体和12个gp 5五聚体组成，以二十面体对称组织。Gp 5由N-末端Delta结构域（11 kDa）和gp 5 *（31 kDa）组成：gp 5 * 形成连续的壳，A结构域簇从该壳向内延伸。在中性pH下，Prohead I在53 ° C下表现出吸热转变，焓变为14 kcal/mole（gp 5单体）。我们表明，这种转变是可逆的。为了捕获其结构表达，我们在60 ℃下孵育Prohead I，然后快速冷冻，并通过冷冻-EM观察到比Prohead I大10%的衣壳种类。在11埃分辨率下，可见的变化仅限于gp 5六聚体。它们的三角洲域簇已经消失，可能是无序的，要么是展开的，要么是分散的。gp 5 * 六聚体环变薄和变平，因为它们呈现在扩展中间体1中观察到的构象，这是正常的蛋白水解诱导的成熟途径的过渡状态。我们推断，在环境温度下，六聚体A-结构域抑制它们的gp 5 * 环切换到较低的自由能，EI-I样，状态;高于53度，这种抑制被克服。另一方面，五聚体更稳定地锚定并抵抗这种热扰动。(c)2006年爱思唯尔公司All rights reserved.
Scanning calorimetry combined with cryo-clectron microscopy affords a powerful approach to investigating hierarchical interactions in multi-protein complexes. Calorimetry can detect the temperatures at which certain interactions are disrupted and cryo-EM can reveal the accompanying structural changes. The procapsid of bacteriophage HK97 (Prohead 1) is a 450 angstrom-diameter shell composed of 60 hexamers and 12 pentamers of gp5, organized with icosahedral symmetry. Gp5 consists of the N-terminal Delta-domain (11 kDa) and gp5* (31 kDa): gp5* forms the contiguous shell from which clusters of A-domains extend inwards. At neutral pH, Prohead I exhibits an endothermic transition at 53 degrees C with an enthalpy change of 14 kcal/mole (of gp5 monomer). We show that this transition is reversible. To capture its structural expression, we incubated Prohead I at 60 degrees C followed by rapid freezing and, by cryo-EM, observed a capsid species 10% larger than Prohead I. At 11 angstrom resolution, visible changes are confined to the gp5 hexamers. Their Delta-domain clusters have disappeared and are presumably disordered, either by unfolding or dispersal. The gp5* hexamer rings are thinned and flattened as they assume the conformation observed in Expansion Intermediate 1, a transition state of the normal, proteolysis-induced, maturation pathway. We infer that, at ambient temperatures, the hexamer A-domains restrain their gp5* rings from switching to a lower free energy, EI-I-like, state; above 53 degrees, this restraint is overcome. Pentamers, on the other hand, are more stably anchored and resist this thermal perturbation. (c) 2006 Elsevier Inc. All rights reserved.