Relaxation Optimized SAIL Method for Studying Structures and Dynamics
of Proteins and Protein Complexes
Masatsune Kainosho
Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachioji, Tokyo, 192-0397 Japan;
& Structural Biology Research Center, Graduate School of Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya, 464-8601 Japan
ABSTRACT
The Stereo-Array Isotope Labeling (SAIL) method has been successfully applied for structure
determinations of proteins as large as 50 kDa, which are unamenable to conventional NMR
methods.1) Unfortunately, the high cost of preparing a protein exclusively composed of SAIL
amino acids by utilizing the cell-free protein expression system has hampered the
dissemination of this sophisticated labeling method throughout the NMR community.
However, there are various applications of the SAIL method besides structure determinations,
for which proteins labeled with selected types of SAIL amino acids should be sufficient.
This type of approach, denoted as the selective SAIL method, is economically feasible and
also practical, since cell-free protein expression is not required for preparing the NMR
samples. In integrated structural biology research, the major role of NMR spectroscopy has
shifted from structure determinations to elucidations of the dynamics and interactions of
biologically interesting protein complexes.
In view of this recent trend in biological NMR spectroscopy, we describe our results over the
past few years with the selective SAIL method, utilizing redesigned SAIL amino acids in
order to implement improved relaxation properties. The new types of SAIL amino acids,
designated as relaxation optimized SAIL amino acids, allow us to observe NMR signals for
all atoms in the amino acid side-chains, including the aromatic ring, methylene, and methine
groups, even for proteins as large as 80 kDa. The relaxation optimized SAIL approach will fill
the gap between the methyl only approach and the conventional NMR methods, and thus
facilitate various investigations of protein dynamics with wider amplitudes and time-scale
ranges for protein complexes. Some of our recent results along this line will be presented.
1)
Kainosho M, Torizawa T, Iwashita Y, Terauchi T, Ono A M, Güntert P (2006), Nature, 440: 52-57.