Collins C M, Collier R J
Biochim Biophys Acta. 1985 Apr 5;828(2):138-43. doi: 10.1016/0167-4838(85)90049-4.
We have recorded the near- and far-ultraviolet circular dichroism spectra of diphtheria toxin, Pseudomonas aeruginosa exotoxin A, and derivatives of these toxins. The far-ultraviolet spectra of various forms of diphtheria toxin were virtually identical, implying that no major changes in secondary structure accompany proteolytic nicking or dimerization of toxin, or binding of the endogenous dinucleotide, adenylyl-(3'-5')-uridine 3'-monophosphate (AdoPUrdP). Alpha-helix content was estimated to be 29%, as compared with 8% for fragment A. Near-ultraviolet spectra were identical between nicked and intact diphtheria toxin. A broad negative transition with a minimum at 304 nm was assigned to the intrachain disulfide bridge within the B moiety. Dimeric diphtheria toxin showed perturbations of aromatic residues. Binding of AdoPUrdP to monomeric diphtheria toxin or of adenylyl-(3',5')-uridine (AdoPUrd) to fragment A perturbed one or more tryptophans. The latter results correlate with evidence for involvement of a tryptophan in NAD binding. Native exotoxin A was estimated to have 16% alpha-helix, and the activated form of exotoxin A, 11%. An enzymically active, 31 kDa proteolytic fragment of exotoxin A showed similar alpha-helix content (7%) to that of diphtheria toxin fragment A.
我们记录了白喉毒素、铜绿假单胞菌外毒素A及其毒素衍生物的近紫外和远紫外圆二色光谱。各种形式的白喉毒素的远紫外光谱实际上是相同的，这意味着毒素的蛋白水解切口或二聚化、内源性二核苷酸腺苷酰-（3'-5'）-尿苷3'-单磷酸（AdoPUrdP）的结合都不会伴随二级结构的重大变化。估计α-螺旋含量为29%，而片段A为8%。切口的和完整的白喉毒素的近紫外光谱是相同的。在B部分内的链内二硫键被指定为在304nm处有最小值的宽负跃迁。二聚体白喉毒素显示出芳香族残基的扰动。AdoPUrdP与单体白喉毒素的结合或腺苷酰-（3'，5'）-尿苷（AdoPUrd）与片段A的结合会扰动一个或多个色氨酸。后一结果与色氨酸参与NAD结合的证据相关。天然外毒素A估计有16%的α-螺旋，外毒素A的活化形式有11%。外毒素A的一个具有酶活性的31kDa蛋白水解片段显示出与白喉毒素片段A相似的α-螺旋含量（7%）。
