Gonadotropin and subunit conformation.
Gonadotropin and subunit conformation.
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促性腺激素和亚基构象。
DOI：
10.1016/0003-9861(75)90083-1
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发表时间：
1975
影响因子：
3.9
通讯作者：
D. Puett
中科院分区：
文献类型：
--
作者：
L. Holladay;D. Puett
圆二色性光谱已获得和解决的促性腺激素，羊垂体促黄体激素和人绒毛膜（尿）促性腺激素，它们的亚基和糖肽。250 nm以上的促性腺激素椭圆率大部分可归因于二硫化物发色团，尽管酪氨酰和苯丙氨酰残基也有明显的贡献。在两种不同的亚基中，β亚基对促性腺激素的近紫外圆二色性光谱的贡献最大。从0-0酪氨酰条带的位置，即，286-287 nm，可以确定促性腺激素的至少一些酪氨酰残基位于疏水环境中。在232.5nm处有一个正圆二色性极值，它存在于黄体生成素中，而不存在于绒毛膜促性腺激素中，可归因于α亚基，可能是黄体生成素中酪氨酸21和/或30的结果。通过从每种促性腺激素的分子椭圆率中减去各个亚基的分子椭圆率之和而产生，表明当促性腺激素解离时，二硫键和酪氨酰残基的局部环境会发生改变。两个α-亚基和两个β-亚基之间的圆二色性差异光谱表明，主要的贡献来自-酪氨酰残基，推测是由酪氨酰取代引起的。黄体生成素和绒毛膜促性腺激素的极值分别出现在210 nm和207.5 nm处。每个极值可以通过两个负分辨带来描述，一个在215 nm处，另一个在207和208.5 nm之间。215 nm分辨带归属于β-折叠片构象的肽发色团，没有α-螺旋性的证据。较低波长的分辨带被认为具有来自葡糖胺、半乳糖胺和唾液酸的N-乙酰基的显著贡献，特别是因为通过用链霉蛋白酶消化S-羧甲基衍生物从每种促性腺激素制备的糖肽级分，在207 nm处有一个负的圆二色性极值，两种促性腺激素的β-结构的程度估计约为28%而分离的亚基含有较少的β-结构，例如，α-和β-亚基分别约为21%和13%。亚基β-结构的总和（针对每个亚基的相应分子量校正）约为17%。这是基本上小于天然激素，从而表明显着的构象变化发生在促性腺激素解离的生物活性亚基。此外，促性腺激素β结构的一部分可能来自分子间氢键，涉及亚基之间的折叠片排列。
Circular dichroic spectra have been obtained and resolved for the gonadotropins, ovine pituitary luteinizing hormone and human chorionic (urinary) gonadotropin, their subunits and glycopeptides. Much of the gonadotropin ellipticity above 250 nm can be attributed to the disulfide chromophore, although there are discernible contributions from tyrosyl and phenylalanyl residues as well. Of the two dissimilar subunits, the β-subunit makes the greatest contribution to the near-ultraviolet circular dichroic spectrum of the gonadotropins. From the position of the 0-0 tyrosyl band, i.e., 286–287 nm, one can ascertain that at least some of the tyrosyl residues of the gonadotropins are located in a hydrophobic environment. A positive circular dichroic extremum at 232.5 nm, present in luteinizing hormone but not in chorionic gonadotropin, can be ascribed to the α-subunit and probably results from tyrosines 21 and/or 30 in luteinizing hormone.An analysis of the circular dichroic difference spectrum above 230 nm, generated by subtracting the sum of the molecular ellipticities of the respective subunits from the molecular ellipticities of each gonadotropin, indicates that the local environment of disulfides and of tyrosyl residues is altered when gonadotropins dissociate. Circular dichroic difference spectra between the two α-subunits and between the two β-subunits indicated major contributions from- tyrosyl residues, presumably arising from tyrosyl substitutions.Between 200 and 230 nm, both gonadotropins exhibit negative circular dichroic extrema. The extremum occurs at 210 nm for luteinizing hormone and at 207.5 nm for chorionic gonadotropin. Each extremum can be described by two negative resolved bands, one at 215 nm and the other between 207 and 208.5 nm. The 215-nm resolved band is assigned to the peptide chromophore in a β-pleated sheet conformation and there is no evidence of α-helicity. The lower-wavelength resolved band is believed to have a significant contribution from theN-acetyl groups of glucosamine, galactosamine, and sialic acid, particularly since the glycopeptide fractions, prepared from each gonadotropin by digestion of theS-carboxymethyl derivatives with Pronase, exhibited a negative circular dichroic extremum at about 207 nm.The extent of β-structure in both gonadotropins is estimated to be about 28% whereas the separated subunits contain less β-structure, e.g., about 21 and 13% for the α- and β-subunits, respectively. The sum of the subunit β-structure, corrected for the respective molecular weight of each subunit, is about 17%. This is substantially less than that of the native hormone, thus indicating that significant conformational changes occur during gonadotropin dissociation to the biologically inactive subunits. Also, part of the gonadotropin β-structure may arise from intermolecular hydrogen bonding involving a pleated sheet arrangement between the subunits.