Re: [modeller_usage] Question about chi dihedral angle cubic spline restraint
To: "Lee, Jinhyuk" <>
Subject: Re: [modeller_usage] Question about chi dihedral angle cubic spline restraint
From: Modeller Caretaker <>
Date: Fri, 22 Jan 2010 13:09:25 -0800
Cc:
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.