Molybdenum disulfide (MoS2), a new type of transition metal dichalcogenides nanomaterial, has attracted significant attention lately in the biomedical industry, with many promising applications such as photothermal-triggered drug delivery agent for cancer. Accompanied with these promising applications are the growing concerns about their potential biocompatibility. Here, we use all-atom molecular dynamics simulations to investigate the interaction of a MoS2 nanotube with YAP65 WW domain, a mostly antiparallel β-sheet model protein widely used in molecular simulations. We find that YAP65 loses most of its secondary and tertiary structures within a few hundred nanoseconds after adsorbing onto the MoS2 nanotube surface, indicating that the MoS2 nanotube displays significant structural damage to YAP65. The strong dispersion interactions, especially from those "signature" aromatic residues (Tyr28 and Trp39), help drive YAP65 adsorption onto the nanotube surface, which thus breaks the native beta strand hydrogen bond network and subsequently destroys the secondary and tertiary structures. These findings might shed new light onto the potential nanotoxicity of MoS2 nanomaterial and its underlying molecular mechanism. (Figure Presented).