Mechanical unfolding of the fourth domain of Distyostelium discoideum filamin (DDFLN4) was studied in detail using the C(alpha)-Go model. We show that unfolding pathways of this protein depend on the pulling speed. The agreement between theoretical and experimental results on the sequencing of unfolding events is achieved at low loading rates. The unfolding free energy landscape is also constructed using dependencies of unfolding forces on pulling speeds.