Effects of salt concentration on association of the amyloid protofilaments of hen egg white lysozyme studied by time-resolved neutron scattering

Fujiwara, Satoru; Matsumoto, Fumiko*; Yonezawa, Yasushige*

The kinetic process of the fibril formation of hen egg white lysozyme (HEWL) in 90% ethanol in various salt concentrations has been investigated with time-resolved neutron scattering. It was shown that by addition of NaCl in a range between 0.3 mM and 1.0 mM, gelation occurred, and this gelation proceed through a two-step process; the lateral association of the protofilaments formed by HEWL, followed by the cross-linking of these fibrils formed. Both the structures of the fibrils and the rate of the gelation depended on NaCl concentration. Above 2 mM NaCl, precipitation occurred because of the formation of amorphous aggregates. Sensitivity of the aggregated structures to salt concentration suggests that electrostatic interaction plays an essential role in the formation of these structures. The structural diversity both in the fibrils and the aggregated structures of the fibrils can be interpreted in terms of the difference in the degree of the electrostatic shielding at different salt concentrations.