The Large Subunit of Leishmania Topoisomerase I Functions as the ‘molecular steer’ in Type IB Topoisomerase
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The Large Subunit of Leishmania Topoisomerase I Functions as
the ‘molecular steer’ in Type IB Topoisomerase
Bose Dasgupta, Somdeb
Khalkho, Neeta V M
Majumder, Hemanta K.
Infectious Diseases and Immunology
Kinetoplastid topoisomerase IB is an unusual
bisubunit enzyme where reconstitution of the large
(LdTOPIL or L) and small (LdTOPIS or S) subunits
shows functional activity. It is yet to be deciphered
whether one subunit or both navigate the heterodimer
to its cellular DNA targets. Tethering a specific
DNA-binding protein to topoisomerase I alters its
site specificity. The chimeric constructs UMSBP–
LdTOPIL/S or U–L/S (fusion of UMSBP to the Nterminus
of L and reconstituted with S) and LdTOPIL/
UMSBP–LdTOPIS or L/U–S (fusion of UMSBP to the
N-terminus of S and reconstituted with L) exhibit relaxation
activity.Only U–L/S shows altered site specificity
and enhanced DNA-binding affinity for the universal
minicircle sequence (UMS) containing substrate. This
proves that L alone serves as the ‘molecular steer’ for
this heterodimer. Reconstituted U–L/S also induces
cleavage close to UMS and causes minicircle linearization.
The differential properties of the reconstituted
chimeras U–L/S and L/U–S reveal the structural and
functional asymmetry between the heterodimer.
Therefore this study helps in a better understanding of
the mechanistic details underlying topoisomerization
by this bi-subunit enzyme.
Bose Dasgupta, Somdeb and Ganguly, Agneyo and Das, BB and Roy, Amit and Khalkho, Neeta V M and Majumder, Hemanta K. (2008) The Large Subunit of Leishmania Topoisomerase I Functions as the ‘molecular steer’ in Type IB Topoisomerase. Molecular Microbiology, 67 (1). pp. 31-46.