The adsorption of streptavidin is studied on two surfaces, graphite and titanium dioxide, using accelerated molecular dynamics. Adsorption on graphite leads to strong conformational changes while the protein spreads out over the surface. Interestingly, also adsorption on the highly hydrophilic rutile surface induces considerable spreading of the protein. We pin down the cause for this unfolding to the interaction of the protein with the ordered water layers above the rutile surface. For special orientations, the protein penetrates the ordered water layers and comes into direct contact with the surface where the positively charged amino acids settle in places adjacent to the negatively charged top surface atom layer of rutile. We conclude that for both surface materials studied, streptavidin changes its conformation so strongly that it loses its potential for binding biotin. Our results are in good qualitative agreement with available experimental studies.