Biomacromolecular Neutron Crystallography

The Basic Principles of Neutron Protein Crystallography

Abstract

Hydrogen (H) atoms and proton (H⁺) of biomacromolecules are important for various biological phenomena. H atoms of functional groups such as -OH and -NH₂ make hydrogen bonds to contribute to folding and assembly of biomacromolecules. H⁺ ions are used for chemical reaction, electron transfer, and H⁺ concentration gradient is an energy source in cells.

X-ray crystallography is the most popular technique for structure determination of biomacromolecules, however it is very difficult to determine H atoms and almost impossible to identify H⁺ ions, because X-ray diffracts by electron cloud. On the other hand, neutron scattering length of H, H⁺, and its isotope (deuterium: D and D⁺) are comparable to those of non-hydrogen atoms in biomacromolecules. Therefore, the complementary use of X-ray and neutron crystallography provides detailed structural information of biomacromolecules including H and H⁺. So far, protein has been the main subject of biomacromolecular neutron crystallography; this technique is also called neutron protein crystallography (NPC). In this report, the basic principles of NPC are described.