On 1/22/10 7:42 AM, Lee, Jinhyuk wrote: > I have a question about chi dihedral angle in rsr (restraint) file. > > The following is one of chi1 dihedral angles. > > R 10 22 3 14 4 28 0 1 2 3 4 1.0000 > -3.1416 3.1584 0.3000 0.1072 -1.8388 0.3519 0.5736 > 1.8270 4.1095 4.6770 1.6637 0.1167 0.0925 1.5911 > 4.6125 7.2224 6.4874 3.6210 1.5701 0.8375 1.4232 > 3.3272 6.1649 5.4708 2.8728 1.0891 0.3370 > > I think that the 14th and 15th columns (-3.1416 and 3.1584) > represent the low and high points, respectively.

You are correct.

> Is there any reason of using -3.1416 and 3.1584 not pi and -pi?

While modern Modeller supports both open and closed (non-periodic and periodic) cubic splines, when the chi1 statistics were originally generated it only supported open cubic splines, and so the dihedral restraints are actually non-periodic (they were kludged so that the values at -pi and pi are the same, but the derivatives are likely discontinuous).

The reason the upper value is 3.1584 rather than 3.1416 is simply rounding error; -3.1416 + 21*0.3000. When the statistics were originally collected it was probably felt that specifying a bin size of 0.3 was close enough to 0.29919... radians.

Ben Webb, Modeller Caretaker