In order to better understand the process of cell entry for non-enveloped viruses, we have solved the crystal structures of five poliovirus mutants which can infect cells expressing mutant poliovirus receptors. Four of these structures have been solved from frozen crystals using cryocrystallographic data collection methods. The mutations have a range of structural consequences, from small local perturbations to significant loop rearrangements. All of the mutant viruses are more labile to conversion to an apparent cell entry intermediate, suggesting that these mutant viruses could compensate for the suboptimal receptors by lowering the thermal energy required to undergo the receptor-mediated conformational change.