Katayama Hidekazu, Mita Masatoshi
Department of Bioengineering, School of Engineering, Tokai University, 4-1-1, Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan.
Department of Biochemistry, Showa University School of Medicine, 1-5-8, Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
Gen Comp Endocrinol. 2023 Apr 1;334:114226. doi: 10.1016/j.ygcen.2023.114226. Epub 2023 Jan 31.
A relaxin-like gonad-stimulating peptide (RGP) in starfish was the first identified invertebrate gonadotropin, consisting of A- and B-chain. Recently, an RGP ortholog (Asc-RGP) from Astropecten scoparius in the order Paxillosida was found to harbor an amidation signal (Gly-Arg) at the C-terminus of the B-chain (Mita et al., 2020a). Two cleavage sites were also predicted within the signal peptide of the Asc-RGP precursor. Thus, four kinds of analogs (Asc-RGP-NH(S), Asc-RGP-GR(S), Asc-RGP- NH(L), Asc-RGP-GR(L) were hypothesized as natural Asc-RGPs. To identify the natural Asc-RGP, an extract of radial nerve cords from A. scoparius was analyzed using reverse-phase high-performance liquid chromatography and MALDI-TOF-mass spectrometry. The molecular weight of Asc-RGP was 4585.3, and those of A- and B-chains were 2511.8 and 2079.8, respectively. This strongly suggests that natural RGP in A. scoparius is Asc-RGP-NH(S). Asc-RGP-NH(S) stimulated 1-methyladenine and cyclic AMP production in isolated ovarian follicle cells of A. scoparius. On the other hand, the concentrations of four synthetic Asc-RGP analogs required for the induction of spawning in 50% of ovarian fragments were almost the same. The size and C-terminal amidation of the B-chain might not be important for spawning-inducing activity. C-terminally amidated RGPs in the B-chain were also observed in other species of starfish belonging to the order Paxillosida, particularly the family Astropectinidae, but not the family Luidiidae.
海星中的一种类松弛素促性腺刺激肽（RGP）是首个被鉴定出的无脊椎动物促性腺激素，由A链和B链组成。最近，在栉海星目中的日本 Astropecten scoparius 中发现了一种RGP直系同源物（Asc-RGP），其B链的C末端含有一个酰胺化信号（Gly-Arg）（Mita等人，2020a）。在Asc-RGP前体的信号肽内还预测到了两个切割位点。因此，推测有四种类似物（Asc-RGP-NH(S)、Asc-RGP-GR(S)、Asc-RGP-NH(L)、Asc-RGP-GR(L)）为天然的Asc-RGPs。为了鉴定天然的Asc-RGP，使用反相高效液相色谱和基质辅助激光解吸电离飞行时间质谱对日本 Astropecten scoparius 的放射神经索提取物进行了分析。Asc-RGP的分子量为4585.3，A链和B链的分子量分别为2511.8和2079.8。这有力地表明，日本 Astropecten scoparius 中的天然RGP是Asc-RGP-NH(S)。Asc-RGP-NH(S)刺激了日本 Astropecten scoparius 分离的卵巢卵泡细胞中1-甲基腺嘌呤和环磷酸腺苷的产生。另一方面，诱导50%的卵巢碎片产卵所需的四种合成Asc-RGP类似物的浓度几乎相同。B链的大小和C末端酰胺化可能对产卵诱导活性并不重要。在属于栉海星目的其他海星物种中，特别是 Astropectinidae 科，但在 Luidiidae 科中未观察到B链C末端酰胺化的RGPs。
