# Copyright (c) 2002-08 Peter Guntert. All rights reserved.
## 7MACROS: ssbond - CYANA macro
##
## Parameters: <parameters>
##
## Creates the standard upper and three lower limit distance restraints
## (Williamson et al., 1985) to enforce disulfide bonds between pairs R1-R2,
## R3-R4 etc. of cystine residues. These residues must be of the type "CYSS".
## For a disulfide bridge between residues i and j, three upper limits and
## three lower limits are generated:
## [6]

var info echo i j res res1 res2

syntax *

if (nparam.eq.0) return
info:=none; echo:=off
do i 1 nparam
  res='$p$i'
  j=index(res(2:),'-')+1
  if (j.lt.2) error "Illegal residue number pair \"$res\"."
  res1=$res(1:j-1); res2=$res(j+1:)
  if (rnam(irnum(res1)).ne.'CYSS' .or. rnam(irnum(res2)).ne.'CYSS') \
    error "Non-CYSS residue in disulfide bond."
  distance make "SG $res1" "SG $res2" lol=2.0 upl=2.1
  distance make "SG $res1" "CB $res2" lol=3.0 upl=3.1
  distance make "CB $res1" "SG $res2" lol=3.0 upl=3.1
end do
unset info
print "    Restraints for $nparam disulphide bridges added."