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Crystal structures of the regulatory subunit of Thr‐sensitive aspartate kinase from Thermus thermophilus
Author(s) -
Yoshida Ayako,
Tomita Takeo,
Kono Hidetoshi,
Fushinobu Shinya,
Kuzuyama Tomohisa,
Nishiyama Makoto
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2009.07030.x
Subject(s) - thermus thermophilus , protein subunit , kinase , chemistry , biology , crystallography , biochemistry , gene , escherichia coli
Crystal structures of the regulatory subunit of Thr‐sensitive aspartate kinase (AK; EC 2.7.2.4) from Thermus thermophilus (TtAKβ) were determined at 2.15 Å in the Thr‐bound form (TtAKβ‐Thr) and at 2.98 Å in the Thr‐free form (TtAKβ‐free). Although both forms are crystallized as dimers, the contact surface area of the dimer interface in TtAKβ‐free (3200 Å 2 ) is smaller than that of TtAKβ‐Thr (3890 Å 2 ). Sedimentation equilibrium analyzed by ultracentrifugation revealed that TtAKβ is present in equilibrium between a monomer and dimer, and that Thr binding shifts the equilibrium to dimer formation. In the absence of Thr, an outward shift of β‐strands near the Thr‐binding site (site 1) and a concomitant loss of the electron density of the loop region between β3 and β4 near the Thr‐binding site are observed. The mechanism of regulation by Thr is discussed on the basis of the crystal structures. TtAKβ has higher thermostability than the regulatory subunit of Corynebacterium glutamicum AK, with a difference in denaturation temperature ( T m ) of 40 °C. Comparison of the crystal structures of TtAKβ and the regulatory subunit of C. glutamicum AK showed that the well‐packed hydrophobic core and high Pro content in loops contribute to the high thermostability of TtAKβ.