 |
|
Title
|
|
Structural basis for stabilization of Z-DNA by cobalt hexaammine and magnesium cations.
|
|
|
Authors
|
|
R.V.Gessner,
G.J.Quigley,
A.H.Wang,
G.A.van der Marel,
J.H.van Boom,
A.Rich,
A.Rich.
|
|
|
Ref.
|
|
Biochemistry, 1985,
24,
237-240.
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
In the equilibrium between B-DNA and Z-DNA in poly(dC-dG), the [Co(NH3)6]3+ ion
stabilizes the Z form 4 orders of magnitude more effectively than the Mg2+ ion.
The structural basis of this difference is revealed in Z-DNA crystal structures
of d(CpGpCpGpCpG) stabilized by either Na+/Mg2+ or Na+/Mg2+ plus [Co(NH3)6]3+.
The crystals diffract X-rays to high resolution, and the structures were refined
at 1.25 A. The [Co(NH3)6]3+ ion forms five hydrogen bonds onto the surface of
Z-DNA, bonding to a guanine O6 and N7 as well as to a phosphate group in the ZII
conformation. The Mg2+ ion binds through its hydration shell with up to three
hydrogen bonds to guanine N7 and O6. Higher charge, specific fitting of more
hydrogen bonds, and a more stable complex all contribute to the great
effectiveness of [Co(NH3)6]3+ in stabilizing Z-DNA.
|
|
|
|