Effective techniques to prepare iodine derivatives for I-SAD phasing by vaporizing iodine labelling (VIL) and hydrogen peroxide VIL (HYPER-VIL)

RIKEN Advanced Development and Supporting Center Biomolecular Characterization Team* PharmAxess, Inc., Japan**
○Hideyuki Miyatake* Tomokazu Hasegawa** Akihito Yamano**

One of the most dominant factors for successful SAD phasing, especially in laboratories, seems to greatly depend on whether we can extract large enough anomalous effects from collected data. Iodine atoms diffract softer X-rays with larger anomalous effects (Δf''=6.8e- for Cu-Kα, Δf''=12.1e- for Cr-Kα), which are comparable to those of conventional heavy atoms such as Pt and Hg. Thus, if we could effectively incorporate iodine atoms into the target native crystals, this will greatly increase the chances of successful phasing by I-SAD using softer X-rays. That because we developed two effective techniques to prepare iodine derivatives, termed as vaporizing iodine labeling (VIL) and hydrogen peroxide VIL (HYPER-VIL), where vapor diffusion of iodine and hydrogen peroxide plays a key role. By the proposed techniques, we can sometimes prepare iodine derivatives with highly occupied binding sites at the ortho-positions of tyrosine residues, which contributes sufficient phasing power for structure determination. Details and limitations of the VIL and HYPER-VIL will be discussed.

Reference: Miyatake, H., Hasegawa, T. & Yamano, A. (2006). Acta Cryst. D62, 280-289.