Structural features of mammalian gonadotropins
Structural features of mammalian gonadotropins
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DOI：
10.1016/s0303-7207(96)03945-7
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发表时间：
1996-12-20
影响因子：
4.1
通讯作者：
Moore, WT
中科院分区：
文献类型：
--
作者：
Bousfield, GR;Butnev, VY;Moore, WT
有两种动物容易获得垂体和胎盘促性腺激素：人类和马。人类促性腺激素比马促性腺激素具有更好的特征。然而，后者非常有趣，因为它们为源自人类和其他哺乳动物促性腺激素研究的一些一般结构功能原理提供了例外。例如，单独的基因编码 hLH β 和 hCG β 亚基，而单个基因编码 eLH β 和 eCG β。因此，eCG 和 eLH 的不同之处仅在于它们的寡糖部分，并且 eLH 是唯一具有 O-糖基化 C 末端延伸的 LH，此前认为该延伸仅限于绒毛膜促性腺激素。涉及 eLH beta 和 hCG beta 的截短实验表明 C 末端延伸对受体结合没有影响。然而，三种 eCG 形式中最大的一种（仅 O-糖基化程度不同）对 LH 和 FSH 受体的亲和力降低。这一结果表明，在检查 eLH 和 eCG 之间的糖基化差异时，需要考虑 O-糖基化的影响，从而导致 eCG 受体结合亲和力比 eLH 低 10 倍。使用肽-N-聚糖酶消化天然马 α 亚基制剂选择性去除后，评估了 α Asn(56) N 连接寡糖对 eLH 和 eCG 不同生物活性的贡献。在 eLH、eFSH 和 eCG 的 α Asn(56) 上观察到激素特异性糖基化模式。 α Asn(56) 寡糖的去除增加了亚基缔合率、缔合程度和受体结合活性。一些未关联的α亚基寡糖被鉴定出，它们可能干扰亚基关联，因为它们在未关联的亚基寡糖图谱中比在总寡糖图谱中更丰富。这在 eCG α 的情况下最为引人注目，其中两个小峰成为在与 eLH β 和 eFSH β 关联后在不相关的 eCG α 部分中可检测到的主要寡糖峰。混合激素 eLH α 与 oLH β 和 pLH β 相关的生物活性被发现大于 oLH 和 pLH 的生物活性，这为 β 亚基决定异二聚体效力的一般规则提供了一个有趣的例外。 eLH β-嵌合羊/马 α 亚基的 LH 受体结合活性表明，马 α 亚基 N 末端结构域可能是造成这种效应的原因。马 FSH 比人、羊和猪 FSH 制剂具有更高的 FSH 受体结合活性。这可能是由两个因素造成的。首先，如上所述，马α亚基的存在促进受体结合。其次，eFSH β 决定簇环的整体 -2 电荷比其他物种中观察到的 -3 负电荷要小，这是由于第 88 位存在 Asn 残基而不是 Asp。这显然有利于与 FSH 受体的结合。版权所有 (C) 1996 Elsevier Science Ireland Ltd.
There are two species for which both pituitary and placental gonadotropins are readily available, humans and horses. The human gonadotropins are better characterized than equine gonadotropins. Nevertheless, the latter are very interesting because they provide exceptions to some of the general structure-function principles derived from studies on human and other mammalian gonadotropins. For example, separate genes encode the hLH beta and hCG beta subunits while a single gene encodes eLH beta and eCG beta. Thus, eCG and eLH differ only in their oligosaccharide moieties and eLH is the only LH that possesses the O-glycosylated C-terminal extension previously believed to be restricted to chorionic gonadotropins. Truncation experiments involving eLH beta and hCG beta have suggested the C-terminal extension has no effect on receptor binding. However, the largest of three eCG forms which differ only in the extent of O-glycosylation possessed reduced affinity for LH and FSH receptors. This result suggested that effects of O-glycosylation need to be considered when examining the glycosylation differences between eLH and eCG responsible for the 10-fold lower eCG receptor binding affinity compared with that of eLH. Contribution of alpha Asn(56) N-linked oligosaccharides to the different biological activities of eLH and eCG has been evaluated following selective removal using peptide-N-glycanase digestion of native equine alpha-subunit preparations. Hormone-specific patterns of glycosylation were observed on alpha Asn(56) of eLH, eFSH, and eCG. Removal of alpha Asn(56) oligosaccharides increased the rate of subunit association, the extent of association, and receptor binding activity. Some unassociated alpha-subunit oligosaccharides were identified which may interfere with subunit association because they were more abundant in unassociated subunit oligosaccharide maps than in a total oligosaccharide map. This was most striking in the case of eCG alpha in which two minor peaks became the major oligosaccharide peaks detectable in the unassociated eCG alpha fraction following association with eLH beta and eFSH beta. The biological activities exhibited by hybrid hormones, eLH alpha reassociated with oLH beta and pLH beta, found to be greater than those of oLH and pLH provided an interesting exception to the general rule that the beta-subunit determines the potency of the heterodimer. LH receptor binding activities of eLH beta-chimeric ovine/equine alpha-subunits suggested that the equine alpha-subunit N-terminal domain may be responsible for this effect. Equine FSH has higher FSH receptor binding activity than human, ovine, and porcine FSH preparations. This probably results from two factors. First, the presence of the equine a-subunit promotes receptor binding as noted above. Second, the overall -2 charge of the eFSH beta determinant loop, which is less negative that the -3 observed in other species, results from the presence of an Asn residue at position 88 instead of Asp. This apparently facilitates binding to the FSH receptor. Copyright (C) 1996 Elsevier Science Ireland Ltd.