Transferrin binding protein B and Transferrin binding protein A 2 expand the transferrin recognition range of Histophilus somni

Anastassia K. Pogoutse; Trevor F. Moraes

Next, we asked whether H. somni selectively uses bovine transferrin for growth, or whether its 133 binding of ovine transferrin leads to iron uptake from both of these iron sources. We measured 134 growth in the presence of bovine, ovine, caprine, and human transferrins at various 135 concentrations, as well as in buffer alone ( Figure 1C We wondered if the relatively low levels of growth on ovine and caprine transferrin at 25 µM 145 was due to a lower number of transferrin receptors being expressed at the cell surface under more 146 stringent conditions. This low expression may be due to the sudden shift between an iron-replete 147 and iron-starving environment. To address this, we performed another experiment where we 148 "pre-starved" the cells by growing them under iron-limiting conditions that were not as stringent 149 as those used in the previous experiment (see Methods) . In this case, following the pre-starvation 150 step, cells showed growth in the presence of bovine, ovine, and caprine transferrins at 25 µM 151 when compared to growth on human transferrin or buffer alone ( Figure 1D ). 152