ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Pb2+ specifically cleaves yeast tRNAPhe in orthorhombic crystals at phosphates P18 and P60 in the dihydrouridine (D) and pseudouridine (T) loops, respectively. Although there are three major lead binding sites in the tRNA, it appears that both cleavages are affected by the same lead ion. The P18 site is apparently the same site that is hydrolyzed by Pb2+ in solutions of the tRNA and is the major cleavage site in crystals. It is shown from P32 labeling studies with polynucleotide kinase that the products of Pb2+ cleavage have the 5′-hydroxyls on G18 and C60, and consequently the 3′ phosphates are on D17 and U59. The OH- in the first coordination sphere of the hydroxo complex Pb(OH)+ either directly or through a water molecule abstracts the proton of the 2′-OH of D17. This promotes a nucleophilic attack by 2′-O- on P18 with subsequent cleavage of the P—O5′ ester bond to generate the major Pb2+ cleavage product pG18-A76. The anchoring of the Pb2+ by the T-loop and D-loop residues seemingly provide the right environment for the generation of the hydroxo complex required for the hydrolysis. Additionally the strain of the phosphodiester conformation at P18 enhances the cleavage at that site. The Pb2+-catalyzed cleavage of tRNA exemplifies a mechanism used not only for the hydrolysis of transfer RNA but one potentially used by other RNA-catalyzed reaction utilizing metal ion cofactors.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560260736
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