Protein Engineering, Vol 11, 775-782, Copyright © 1998 by Oxford University Press
A Schulga, F Kurbanov, M Kirpichnikov, I Protasevich, V Lobachov, B Ranjbar, V Chekhov, K Polyakov, Y Engelborghs and A Makarov
Chimeric enzymes were constructed to elucidate the differences in
physicochemical properties of two related bacterial RNases, barnase and
binase. Chimeras (Ba26Bi, Ba73Bi, Ba26Bi73Ba and Bi73Ba) contain six to
thirteen residue substitutions relative to barnase, which are beyond the
active site. The catalytic activity of RNases toward GpU, GpC and poly(I),
as well as conformational distinctions and heat denaturation parameters,
were studied. Thermal denaturation of binase, barnase and chimeric RNases
is a two-state transition. The mutation-induced changes in the free energy
of unfolding of barnase deduced from thermal and urea denaturation nearly
coincide. The kinetic parameters for GpU and GpC demonstrate that the
chimeras fall into two groups: barnase-like and binase-like. This division
is determined by the origin of their C- terminal part (residues 73-110)
which is also responsible for their thermostability at pH 2.4. An inverse
linear dependence was found between kcat for poly(I) and denaturation
temperature of RNases at pH 5.5, which points out that certain lability of
the protein molecule appears to be necessary for efficient polynucleotide
cleavage.
ARTICLES
Comparative study of binase and barnase: experience in chimeric ribonucleases
Centre Bioengineering, Russian Academy of Sciences, Moscow.
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