Activated Ribonucleotides
Undergo a Sugar Pucker Switch
upon Binding to a Single-Stranded RNA Template
- Publication date
- Publisher
Abstract
Template-directed polymerization of chemically activated
ribonucleotide
monomers, such as nucleotide 5′-phosphorimidazolides, has been
studied as a model for nonenzymatic RNA replication during the origin
of life. Kinetic studies of the polymerization of various nucleotide
monomers on oligonucleotide templates have suggested that the A-form
(C3′-<i>endo</i> sugar pucker) conformation is optimal
for both monomers and templates for efficient copying. However, RNA
monomers are predominantly in the C2′-<i>endo</i> conformation when free in solution, except for cytidine, which is
approximately equally distributed between the C2′-<i>endo</i> and C3′-<i>endo</i> conformations. We hypothesized
that ribonucleotides undergo a switch in sugar pucker upon binding
to an A-type template and that this conformational switch allows or
enhances subsequent polymerization. We used transferred nuclear Overhauser
effect spectroscopy (TrNOESY), which can be used for specific detection
of the bound conformation of small-molecule ligands with relatively
weak affinity to receptors, to study the interactions between nucleotide
5′-phosphorimidazolides and single-stranded oligonucleotide
templates. We found that the sugar pucker of activated ribonucleotides
switches from C2′-<i>endo</i> in the free state to
C3′-<i>endo</i> upon binding to an RNA template.
This switch occurs only on RNA and not on DNA templates. Furthermore,
activated 2′-deoxyribonucleotides maintain a C2′-<i>endo</i> sugar pucker in both the free and template-bound states.
Our results provide a structural explanation for the observations
that activated ribonucleotides are superior to activated deoxyribonucleotides
and that RNA templates are superior to DNA templates in template-directed
nonenzymatic primer-extension reactions