2p6z
From Proteopedia
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Enzymatic and Structural Characterisation of Amphinase, a Novel Cytotoxic Ribonuclease from Rana pipiens Oocytes
Overview
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 k(cat)/K(M) with hypersensitive, fluorogenic substrates are 10(4) and 10(2)-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 B(1) or, B(2) 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 A resolution, respectively) reveal that the N terminus is unlikely to play a catalytic, role (but an unusual alpha2-beta1 loop may do so) and the B(2) 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.
About this Structure
2P6Z is a Protein complex structure of sequences from Rana pipiens with and as ligands. Full crystallographic information is available from OCA.
Reference
Enzymatic and structural characterisation of Amphinase, a novel cytotoxic ribonuclease from Rana pipiens oocytes., Singh UP, Ardelt W, Saxena SK, Holloway DE, Vidunas E, Lee HS, Saxena A, Shogen K, Acharya KR, J Mol Biol. 2007 Aug 3;371(1):93-111. Epub 2007 May 10. PMID:17560606
Page seeded by OCA on Wed Jan 23 13:57:15 2008
