Difference in hydration structures between F-actin and myosin subfragment-1 detected by small-angle X-ray and neutron scattering

抄録

Hydration structures around F-actin and myosin subfragment-1 (S1), which play central roles as counterparts in muscle contraction, were investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The radius of gyration of chymotryptic S1 was evaluated to be 41.3±1.1 Å for SAXS, 40.1±3.0 Å for SANS in H₂O, and 37.8±0.8 Å for SANS in D₂O, respectively. The values of the cross-sectional radius of gyration of F-actin were 25.4±0.03 Å for SAXS, 23.4±2.4 Å for SANS in H₂O, and 22.6±0.6 Å for SANS in D₂O, respectively. These differences arise from different contributions of the hydration shell to the scattering curves. Analysis by model calculations showed that the hydration shell of S1 has the average density 10-15% higher than bulk water, being the typical hydration shell. On the other hand, the hydration shell of F-actin has the average density more than 19% higher than bulk water, indicating that F-actin has a denser, unusual hydration structure. The results indicate a difference in the hydration structures around F-actin and S1. The unusual hydration structure around F-actin may have the structural property of so-called “hyper-mobile water” around F-actin.