生物谷報(bào)道：最近科學(xué)家在一種豹蛙（Rana pipiens）的卵細(xì)胞內(nèi)發(fā)現(xiàn)的一種分子或許能提供第一種治療腦癌的藥物,。
豹蛙 Rana pipiens
該分子被稱為Amphinase,，它能識(shí)別腫瘤細(xì)胞表面的多糖，然后結(jié)合到其上,，并且入侵到腫瘤細(xì)胞內(nèi)部使RNA失去活性,，最終導(dǎo)致腫瘤死亡。在發(fā)表于Journal of Molecular Biology上的文章中,，來自英國(guó)Bath大學(xué)和美國(guó)Alfacell公司的科學(xué)家描述了對(duì)于這一分子進(jìn)行的首次完全的結(jié)構(gòu)和化學(xué)性質(zhì)分析的結(jié)果,。
盡管可能被用于多種形式的腫瘤，但是Amphinase最有希望治療的是腦癌,，目前針對(duì)腦癌只能進(jìn)行復(fù)雜的手術(shù)以及化療,。科學(xué)家從北部豹蛙的卵母細(xì)胞中分離出了這種核糖核酸酶,。核糖核酸酶在生物體內(nèi)普遍存在,，它們負(fù)責(zé)整理那些自由飄浮的RNA鏈，通過結(jié)合到分子上從而將其切割成小的片斷,。
在細(xì)胞中RNA起著關(guān)鍵作用的部位,，核糖核酸酶被抑制分子所阻礙。但是由于Amphinase是一種兩棲動(dòng)物的核糖核酸酶,，因此它們可以躲開哺乳動(dòng)物的抑制分子,，然后進(jìn)攻癌癥細(xì)胞。
在治療中,，這些分子將可能被注射到需要的區(qū)域,。由于只和腫瘤細(xì)胞表面的多糖進(jìn)行結(jié)合，因此這類分子對(duì)于其它細(xì)胞不會(huì)產(chǎn)生副作用,。這已經(jīng)是Alfacell公司從該種青蛙體內(nèi)分離出的第二種抗癌核糖核酸酶了,。另一種目前處于惡性間皮瘤臨床試驗(yàn)的最后階段,，這是一種罕見且致命的肺癌，而針對(duì)其它實(shí)體癌癥的臨床試驗(yàn)處于第二,、三階段之間,。（援引教育部科技發(fā)展中心）
原始出處:
Enzymatic and Structural Characterisation of Amphinase, a Novel Cytotoxic Ribonuclease from Rana pipiens Oocytes
Umesh P. Singh1, †, Wojciech Ardelt2, †, Shailendra K. Saxena2, †, Daniel E. Holloway1, †, Eugene Vidunas2, 2, Hung-Suen Lee2, Abha Saxena2, Kuslima Shogen2, , and K. Ravi Acharya1, ,
1Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
2Alfacell Corporation, Bloomfield, NJ 07003, USA
Received 21 March 2007; revised 26 April 2007; accepted 29 April 2007. Edited by M. Guss. Available online 10 May 2007.
Abstract
Besides Onconase (ONC) and its V11/N20/R103-variant, oocytes of the Northern Leopard frog (Rana pipiens) contain another homologue of ribonuclease A, which we named Amphinase (Amph). Four variants (Amph-1–4) were isolated and sequenced, each 114 amino acid residues in length and N-glycosylated at two positions. Sequence identities (a) among the variants and (b) versus ONC are 86.8–99.1% and 38.2–40.0%, respectively. When compared with other amphibian ribonucleases, a typical pattern of cysteine residues is evident but the N-terminal pyroglutamate residue is replaced by a six-residue extension. Amph variants have relatively weak ribonucleolytic activity that is insensitive to human ribonuclease inhibitor protein (RI). Values of kcat/KM with hypersensitive fluorogenic substrates are 104 and 102-fold lower than the maximum values exhibited by ribonuclease A and ONC, respectively, and there is little cytosine/uracil or adenine/guanine discrimination at the B1 or B2 subsites, respectively. Amph variants have cytotoxic activity toward A-253 carcinoma cells that requires intact ribonucleolytic activity. The glycan component has little or no influence over single-stranded RNA cleavage, RI evasion or cytotoxicity. The crystal structures of natural and recombinant Amph-2 (determined at 1.8 and 1.9 Å resolution, respectively) reveal that the N terminus is unlikely to play a catalytic role (but an unusual α2–β1 loop may do so) and the B2 subsite is rudimentary. At the active site, structural features that may contribute to the enzyme's low ribonucleolytic activity are the fixture of Lys14 in an obstructive position, the accompanying ejection of Lys42, and a lack of constraints on the conformations of Lys42 and His107.
Keywords: Amphinase; cytotoxic RNase; X-ray crystallography; enzyme efficiency; substrate specificity
Abbreviations: Amph, Amphinase; Amph-1–4, Amphinases-1–4; CpA, cytidylyl-3′,5′-adenosine; DTT, dithiothreitol; 6-FAM-dArC(dA)2-6-TAMRA and rCA, 6-carboxyfluorescein-dArC(dA)2-6-carboxytetrarhodamine; 6-FAM-dArU(dA)2-6-TAMRA and rUA, 6-carboxyfluorescein-dArU(dA)2-6-carboxytetrarhodamine; 6-FAM-dArUdGdA-6-TAMRA and rUG, 6-carboxyfluorescein-dArUdGdA-6-carboxytetrarhodamine; MTT, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide; ONC, Onconase; PEG, poly(ethylene glycol); PNGase F, peptide-N4-(N-acetyl-β-glucosaminyl)asparagine amidase from Elizabethkingia (Chryseobacterium/Flavobacterium) meningsepticum; rAmph-2, recombinant Amphinase-2; RC-RNase, Rana catesbeiana ribonuclease; RC-RNase-6, Rana catesbeiana ribonuclease-6; RI, ribonuclease inhibitor protein; RNase A, bovine pancreatic ribonuclease A; rRNA, ribosomal RNA; TFA, trifluoroacetic acid; TPCK, N-p-tosyl-L-phenylalanine chloromethyl ketone; UpA, uridylyl-3′,5′-adenosine
Corresponding authors.
† U.P.S., W.A., S.K.S. and D.E.H. contributed equally to this work.
2 Present address: E. Vidunas, Wyeth Pharmaceuticals, Pearl River, NY 10965, USA.
