Crystallization and structure-functional analysis of mutated motor subunits of type I restriction enzyme EcoR124I
Tatsiana Baikova1,2, Mikalai
Lapkouski1, Santosh Panjikar3, Ivana Kuta-Smatanova1,2,
Rudiger Ettrich1,2 and Eva Csefalvay1,2
1Institute of Nanobiology and Structural Biology of ISBE, AS CR, 37333 Nove Hrady, Czech Republic
2University of South Bohemia in České Budějovice, 37333 Nove Hrady, Czech Republic
3EMBL Hamburg Outstation, c/o DESY,
Notkestrasse 85, D22603 Hamburg, Germany
Invasion
of foreign DNA into microorganisms can be prevented by restriction–modification
(R-M) systems. Though Type I R-M enzymes are not
site-specific endonucleases they remain an important area of research mainly
because of their unusual biochemical properties and their unique
mechanisms of DNA translocation and restriction. The crystal structure of the
motor subunit, responsible for translocation and restriction, of the type I
enzyme EcoR124I , resolved at 2.6 A, shows a square-planar arrangement of
globular domains with a prominent cleft that accommodates DNA extending from
the two canonical helicase domains to the endonuclease active site [1].
Unexpectedly, ATP bound in the helicase cleft is also engaged by Lys220 of the
nuclease domain, potentially coupling the nuclease and translocation
activities. To shed light on the coupling mechanism, mutants were designed that
should alter the coupling at this position by influencing DNA cleavage but
leaving the ATPase activity of EcoR124I unaltered. Three-dimensional structural
information is essential to complement experimental data in a way, that lets us
draw conclusions about the molecular mechanism. We discuss mutations of Lys220
to Ala, Arg and Glu, and the successfully solved crystals structures of the
Arg220 and Glu220 mutants, that we determined to 2.74 A (PDB 2w74) and 2.99A
resolution (PDB 2y3t), respectively.
Data
collection of Glu220 crystal was performed on beamline X11 at EMBL/DESY
(Hamburg). Data from 451 images were integrated and scaled with XDS and XSCALE.
The motor subunit Glu220 crystals belong
to space group P21 and unit cell dimensions are a=127.11 A, b=123.11 A,
c=160.11 A, and β=111.48°. The structure was solved by molecular
replacement using Auto-Rickshaw19 and MOLREP programs, and using our previously
solved wild type structure (PDB 2w00) as the search model.
[1] Lapkouski M., Panjikar S., Janscak P., Kuta Smatanova I., Carey J., Ettrich R., Csefalvay E. Nat. Struct. & Mol.Biol, 2009, 16, 94.
We
gratefully acknowledge support from the Ministry of Education, Youth and Sports
of the Czech Republic (MSM6007665808, LC06010), the Academy of Sciences of the
Czech Republic (AVOZ60870520), the Grant Agency of the Czech Republic (Nos.
P207/10/1934), and joint Czech - US National Science Foundation International
Research Cooperation (ME09016 and INT03-09049), Additionally, T.B. was
supported by the University of South Bohemia, grant GAJU 170/2010/P.