Letno poročilo 2005

SLIKA 3:
Vpogled med dve G-kvartetni ravnini, ki sestavljata
G-kvadrupleksno strukturo (na levi). V sredi{~u
vsakega G-kvarteta so prostorsko blizu {tirje O6
karbonilni kisikovi atomi (na levi sliki ozna~eni z
rde~imi kroglicami), katerih nevezni elektronski pari
sodelujejo pri koordinaciji kationov, ki so nujno
potrebni za nastanek G-kvadrupleksne strukture. V
konkretnem primeru je amonijev ion koordiniran z
osmimi O6 karbonilnimi kisikovimi atomi, ki pripadajo
dvema G.kvartetoma. Kationi znotraj tak{nih struktur
ne mirujejo, ampak se izmenjujejo preko odprtin v
G-kvartetnih ravninah. Slika je del {tudije, kjer so P.
[ket, M. ^rnugelj in J. Plavec pokazali, da se znotraj
dimernega G-kvadrupleksa, ki ga tvori oligo-
nukleotidno zaporedje bogato z gvanini d(G 3 T 4 G 4 ),
nahajata dve vezavni mesti za katione. V nadaljevanju
so uspeli dokazati obliko G-kvadrupleksa d(G T G ) ,
3 4 4 2
ki vsebuje K + in 15 + NH ion in predstavlja vmesno
4
stanje v prehodu iz dvo-15 + + NH v dvo-K obliko.
4
Korelacijski signali v ROESY spektru med amonijevimi
ioni in imino protoni gvaninov, ki je prikazan na desni
so dali informacijo o polo`aju amonijevega iona
znotraj te strukture. Rezultati te {tudije so bili
objavljeni v ~lanku z naslovom “Identification of mixed
di-cation forms of G-quadruplex in solution” v reviji
Nucleic Acids Res. (2005, 33, 3691-3697).
Nacionalni center za NMR spektroskopijo visoke lo~ljivosti - lokacija KI
National Centre for High Resolution NMR Spectroscopy - Location NIC
FIGURE 3:
Detailed view into the structure of a G-quadruplex
showing two G-quartet planes (on the left side). There
are four O6 carbonyl oxygen atoms (marked as red
balls) in the middle of each G-quartet, which are involved
in coordination with cations that are essential
for the formation of G-quadruplex structures. Ammonium
ion in the figure is coordinated with eight
O6 carbonyl oxygen atoms belonging to two neighbouring
G-quartet planes. Cations found inside Gquadruplex
structures are undergoing fast and complex
motion through the opening in each G-quartet
plane. Figure is a part of a study in which P. [ket, M.
^rnugelj and J. Plavec have shown that dimeric Gquadruplex
structure adopted by guanine rich se-
quence d(G 3 T 4 G 4 ) exhibits two cation binding sites.
Furthermore, they experimentally demonstrated the
existence of the mixed form of d(G T G ) containing
3 4 4 2
one K + and one 15 + NH ion inside the G-quadruplex
4
core that represents intermediate in the conversion
of di-15 + + NH into di-K form. Cross-peaks in ROESY
4
spectrum between ammonium ions and neighbour-
ing guanine imino protons shown on the right were
used to localize ammonium ions inside the mixed dication
structure. The results of the study were published
in the manuscript entitled “Identification of
mixed di-cation forms of G-quadruplex in solution”
in Nucleic Acids Res. (2005, 33, 3691-3697).
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