Page 80 - Annual Report_21-22

Reversible B-to Z-DNA transition assisted by lanthanum chloride in (CG)n and (GC)n repeats

The transition from right-handed to left-handed DNA is that B-Z transition is reversible in short repeat sequences.
not only acting as the controlling factor for switching gene Thermal melting and annealing behaviour of B-DNA are
expression but also has equal importance in designing reversible while the thermal melting of LaCl -induced
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nanomechanical devices. The (CG) and (GC) repeat Z-DNA is irreversible which suggest a stronger binding
n
n
sequences are well known model molecules to study of LaCl to the phosphate backbone of Z-DNA. This was
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B-Z transition in the a presence of higher concentration further supported by the Isothermal titration calorimetric
of monovalent cations. In this communication, we report study. Molecular dynamics (MD) simulation of d(CG) .
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a cyclic transition in (CG) DNA using the millimolar d(CG) in the presence of LaCl indicates that both GC and
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3
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concentration of trivalent lanthanide salt LaCl . The CG base steps predominantly sample intermediate/ZI/BIII
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controlled and reversible transition was seen in (CG) and conformations rather than the BI/BII conformations (less
12,
(GC) DNA employing CD spectroscopy. While LaCl failed than 1.7%). This, along with the preference for -syn/high-
3
12
to induce B-Z transition in shorter oligonucleotides such anti glycosyl conformations by the G’s further support the
as (CG) and (GC) , a smooth B-Z transition was recorded experimental results. MD simulation also reveals that La
3+
3
3
for (CG) , (CG) 12 and (GC) 12 sequences. Interestingly, interacts with the DNA via the minor groove. Thus, LaCl 3

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the phenomenon was reversible (Z-B transition) with can easily be adopted as aninducerofleft-handed DNA in

the addition of EDTA. Particularly, two rounds of cyclic other short oligonucleotides sequences to understand the
transition (B-Z-B-Z-B) have been noticed in (CG) DNA in molecular mechanism of B-Z transition.
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the presence of LaCl and EDTA which strongly suggest
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78 ANNUAL REPORT 2021-22