Structural Characterization of Myoglobin Molecules Adsorbed within Mesoporous Silicas

In the present study, we examined the secondary and tertiary structure of myoglobin (Mb) within folded sheets mesoporous material (FSM)- and Santa Barbara amorphous (SBA)-type mesoporous silicas. The Barrett-Joyner-Halenda pore diameters of SBA-type mesoporous silicas were 39, 70, and 75 angstrom, and that of FSM-type mesoporous silica was 40 angstrom. The secondary and tertiary structures of myoglobin were observed by Fourier transform infrared (FTIR) and small-angle neutron scattering (SANS), respectively. The FTIR and SANS results indicated preservation of the secondary and tertiary structures of myoglobin inside the pores of SBA-type mesoporous silicas. Adsorption of myoglobin within FSM-type mesoporous silica, however, resulted in perturbation of the tertiary structure, accompanied by partial unfolding of the secondary structure. Lower structural stability of myoglobin within the FSM-type mesoporous silica was also confirmed. These findings suggest that the Mb structure is more influenced by the inner pore surface characteristics than by geometrical pore size.