Recycling Corner/Alpha Helix Generator
RIBOZOME - an Alpha Helix Generator script
Creates an alpha helix from a user input string.
Jmol script by Ron Mignery with help from Angel Herráez
Contents
Script for Jmol application
# RIBOZOME - Jmol script by Ron Mignery with help from Angel Herráez
# v1.2 beta 10/23/2013
#
# New in v1.2 beta:
# No longer zaps existing atoms
# Now adds on to existing helix on subsequent runs
# Fixes proline cross-link bug with XXXXPXP
# Localizes variables and globalizes constants
#
# RIBOZOME takes a string message encoding an amino acid (aa) sequence
# and generates a corresponding alpha helix one aa at a time from the
# N terminus to the C terminus rotating the emerging helix as it goes.
#
# The message is a string entered by the user at a prompt.
# It may be typed in or pasted in and be of any length
# If the message is prepended with <C>: (where C is any single letter)
# then the chain is so labeled and separated from existing chains
# if different from the first chain.
#
# The IUPAC/IUBMB 1 letter code is used:
# A=ALAnine B=GLutam?X* C=CYSteine D=ASPartate E=GLUtamate
# F=PHEnylalanine G=GLYcine H=HIStidine I=IsoLEucine K=LYSine
# L=LEUcine M=METhionine N=ASparagiNe O=PYrroLysine*** P=PROline
# Q=GLutamiNe R=ARGinine S=SERine T=THReonine U=SElenoCysteine
# V=VALine W=TRyPtophan X=UNKnown Y=TYRosine Z=ASpar?X**
# *Either GLU or GLN: drawn as GLN with chi3 flipped
# **Either ASP or ASN: drawn as ASN with chi3 flipped
# ***Not supported: drawn as ALA
# The following constant values determine the pitch of the alpha helix
gPHI = -57 # Dihedral angle of N-CA bond (nominally -57)
gPSI = -47 # Dihedral angle of CA-C bond (nominally -47)
gOMEGA = 180 # Dihedral angle of the peptide bond (nominally 180)
gPEPTIDE_ANGLE = 110 # C-N-CA angle (nominally 110)
gPRO_BUMP = -10 # Psi angle change increment to N-3psi when N is Pro
gCHAIN = 'A' # The chain id
# Lookup 3 letter code from 1 letter code
g3from1 = {"A":"ALA", "B":"GLX","C":"CYS", "D":"ASP","E":"GLU", "F":"PHE",
"G":"GLY", "H":"HIS","I":"ILE", "K":"LYS","L":"LEU", "M":"MET",
"N":"GLN", "O":"PYL","P":"PRO", "Q":"GLN","R":"ARG", "S":"SER",
"T":"THR", "U":"SEC","V":"VAL", "W":"TRP","X":"UNK", "Y":"TYR", "Z":"ASX"}
# Generate PDB atom record
function genAtom(e, aa, i, xyz) {
gA = format("ATOM %5d %4s %3s ", gN, e, aa )
gA += format("%s%4d %8.3f", gCHAIN, i, xyz[1] )
gA += format("%8.3f%8.3f\n", xyz[2], xyz[3] )
gn++
return gA
};
# Generate a PDB amino acid record set
function genAA(i, aa) { # Writes globals gA and gN
# From constructed AAs
var N0 = [0.0, 0.0, 0.0]
var CA = [ 0.200, 1.174, 0.911 ]
var C = [ -1.110, 1.668, 1.425 ]
var O = [ -1.320, 1.693, 2.62 ]
var CB = [ 1.062, 2.1950, 0.230 ]
var G1 = [ 2.359, 1.607, -0.344]
var G2 = [ 1.363, 3.336, 1.157 ]
var D1 = [ 3.222, 2.656, -1.048 ]
var D2 = [ 3.143, 0.904, 0.725 ]
var E1 = [ 3.645, 3.749, -0.167 ]
var E2 = [ 2.491, 3.234, -2.249 ]
var Z = [ 4.470, 4.717, -0.885 ]
var H1 = [ 4.450, 6.006, -0.220 ]
var H2 = [5.833, 4.228, -0.984 ]
var Gp = [ 2.008, 1.24, -0.46 ]
var Dp = [1.022, 0.213, -1.031 ]
var Gfy = [ 2.368, 1.471, -0.0152 ]
var D1fy = [ 3.346, 1.524, 0.921 ]
var D2fy = [ 2.493, 0.516, -1.151 ]
var E1fy = [ 4.513, 0.615, 0.8244 ]
var E2fy = [ 3.528, -0.336, -1.206 ]
var Zfy = [ 4.588, -0.285, -0.168 ]
var Hfy = [ 5.738, -1.245, -0.233 ]
var Ghw = [ 2.406, 1.626, -0.134 ]
var D1hw = [3.498, 1.936, 0.675]
var D2hw = [ 2.713, 0.901, -1.211 ]
var E1hw = [ 4.160, 0.518, -1.178 ]
var E2hw = [ 4.622, 1.160, 0.0816 ]
var E3hw = [ 3.789, 2.523, 1.944 ]
var Z2hw = [ 5.973, 1.177, 0.689 ]
var Z3hw = [ 5.014, 2.550, 2.503 ]
var H2hw = [ 6.153, 1.846, 1.844 ]
#N1 = [ 2.069, -2.122, -0.554]
# Build PDB atom records common to all AAs
a3 = g3from1[aa]
if (a3 = "") {
a3 = "UNK"
}
print format("+ %s%d/%d", a3, i, gSeq.count + gResno)
gA = genAtom(" N ", a3, i, N0)
gA += genAtom(" CA ", a3, i, CA)
gA += genAtom(" C ", a3, i, C)
gA += genAtom(" O ", a3, i, O)
if ((aa != 'G') && (aa != 'X')) {
gA += genAtom(" CB ", a3, i, CB)
}
# Now add AA specific atom records
switch (aa) {
case 'A' :
break;
case 'B' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" CD ", a3, i, D1)
gA += genAtom(" OE1", a3, i, E2) # GLN with Es switched
gA += genAtom(" NE2", a3, i, E1)
break;
case 'C' :
gA += genAtom(" SG ", a3, i, G2)
break;
case 'D' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" OD1", a3, i, D1)
gA += genAtom(" OD2", a3, i, D2)
break;
case 'E' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" CD ", a3, i, D1)
gA += genAtom(" OE1", a3, i, E1)
gA += genAtom(" OE2", a3, i, E2)
break;
case 'F' :
gA += genAtom(" CG ", a3, i, Gfy)
gA += genAtom(" CD1", a3, i, D1fy)
gA += genAtom(" CD2", a3, i, D2fy)
gA += genAtom(" CE1", a3, i, E1fy)
gA += genAtom(" CE2", a3, i, E2fy)
gA += genAtom(" CZ ", a3, i, Zfy)
break;
case 'G' :
break;
case 'H' :
gA += genAtom(" CG ", a3, i, Ghw)
gA += genAtom(" ND1", a3, i, D1hw)
gA += genAtom(" CD2", a3, i, D2hw)
gA += genAtom(" CE1", a3, i, E2hw)
gA += genAtom(" NE2", a3, i, E1hw)
break;
case 'I' :
gA += genAtom(" CG1", a3, i, G1)
gA += genAtom(" CG2", a3, i, G2)
gA += genAtom(" CD1", a3, i, D1)
break;
case 'K' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" CD ", a3, i, D1)
gA += genAtom(" CE ", a3, i, E1)
gA += genAtom(" NZ ", a3, i, Z)
break;
case 'L' :
gA += genAtom(" CG1", a3, i, G1)
gA += genAtom(" CD1", a3, i, D1)
gA += genAtom(" CD2", a3, i, D2)
break;
case 'M' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" SD ", a3, i, D1)
gA += genAtom(" CE ", a3, i, E1)
break;
case 'N' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" OD1", a3, i, D1)
gA += genAtom(" ND2", a3, i, D2)
break;
case 'P' :
gA += genAtom(" CG ", a3, i, GP)
gA += genAtom(" CD ", a3, i, DP)
break;
case 'Q' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" CD ", a3, i, D1)
gA += genAtom(" OE1", a3, i, E1)
gA += genAtom(" NE2", a3, i, E2)
break;
case 'R' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" CD ", a3, i, D1)
gA += genAtom(" NE ", a3, i, E1)
gA += genAtom(" CZ ", a3, i, Z)
gA += genAtom(" NH1", a3, i, H1)
gA += genAtom(" NH2", a3, i, H2)
break;
case 'S' :
gA += genAtom(" OG ", a3, i, G1)
break;
case 'T' :
gA += genAtom(" OG1", a3, i, G1)
gA += genAtom(" CG2", a3, i, G2)
break;
case 'U' :
gA += genAtom("SeG ", a3, i, G1)
break;
case 'V' :
gA += genAtom(" CG1", a3, i, G1)
gA += genAtom(" CG2", a3, i, G2)
break;
case 'W' :
gA += genAtom(" CG ", a3, i, Ghw)
gA += genAtom(" CD1", a3, i, D1hw)
gA += genAtom(" CD2", a3, i, D2hw)
gA += genAtom(" CE2", a3, i, E2hw)
gA += genAtom(" NE1", a3, i, E1hw)
gA += genAtom(" CE3", a3, i, E3hw)
gA += genAtom(" CZ2", a3, i, Z2hw)
gA += genAtom(" CZ3", a3, i, Z3hw)
gA += genAtom(" CH2", a3, i, H2hw)
break;
case 'X' :
gA += genAtom(" Xx ", a3, i, CB)
break;
case 'Y' :
gA += genAtom(" CG ", a3, i, Gfy)
gA += genAtom(" CD1", a3, i, D1fy)
gA += genAtom(" CD2", a3, i, D2fy)
gA += genAtom(" CE1", a3, i, E1fy)
gA += genAtom(" CE2", a3, i, E2fy)
gA += genAtom(" CZ ", a3, i, Zfy)
gA += genAtom(" OH ", a3, i, Hfy)
break;
case 'Z' :
gA += genAtom(" CG ", a3, i, G1)
gA += genAtom(" OD1", a3, i, D2) # ASN with Ds switched
gA += genAtom(" ND2", a3, i, D1)
break;
default :
break;
}
return gA
};
# Generate an alpha helix
function genAlpha(gSeq) {
gN = all.count + 1 # global new N atom index
# Find last linkable N if any
gResno = 0 # global pre-existing AA count
var pn = 1 # previous gN
for (var i = all.count-1; i > 0; i--) {
# If found
if (distance({atomno=i}, {0,0,0}) < 0.1) {
pn = i
# If new chain, separate from existing chain
if ({atomno=i}.chain != gCHAIN) {
select all
translateselected {2.069, -2.122, -0.554 } #N1
}
else {
gResno = {atomno=i}.resno
}
break;
}
}
# For each aa
set appendnew false
var nn = gN # new N
for (var i = 1; i <= gSeq.count; i++) {
# Move polypeptide C to bond distance from new AA N
select all
fix none
translateselected {2.069, -2.122, -0.554 } #N1
# Gen AA
gA = "data \"append aa\"\n" # global PDB atom record
gA += genAA(i + gResno, gSeq[i]); # gN is updated in subroutine
gA += "end \"append aa\""
script inline @{gA}
# If PRO ahead
var pb = 0
if ((gSeq.count - i) >= 2) {
if (gSeq[i + 2] == 'P') {
pb = gPRO_BUMP
}
}
# If not first AA
if (nn > 1) {
# Gen axis on new N perpendicular to the plane
# containing atoms nn, pn+2 and nn+1
var v1={atomno = @{pn+2}}.xyz - {atomno = nn}.xyz
var v2={atomno = @{nn+1}}.xyz - {atomno = nn}.xyz
var axis = cross(v1, v2)
# Center on atom previous C
axis += {atomno = @{pn+2}}.xyz
# Rotate the polypeptide N on the new AA C to tetrahedral (nominally 110)
select atomno < nn
fix atomno >= nn
rotateselected @axis {atomno = nn} @{gPEPTIDE_ANGLE - 69.3}
# Make omega dihedral = gOMEGA (nominally 180)
rotateselected {atomno=@{pn+2}} {atomno=nn} @{gOMEGA - 147.4}
# Make the new phi dihedral = gPHI (nominally -57)
rotateselected {atomno = nn} {atomno = @{nn+1}} @{gPHI - 8.7}
# Make the old psi dihedral = gPSI (nominally -47)
select atomno < @{pn+2} && atomno != @{pn+3}
rotateselected {atomno=@{pn+1}} {atomno=@{pn+2}} @{gPSI + 33.4 + pb}
}
# Step new and previous N
pn = nn
nn = gN
# Make the peptide bond
connect
}
# Clean up
connect ([UNK].CA) ([UNK].Xx and within(group, _1))
select all
fix none
print format("%d atoms generated", gN)
}
echo Generating Alpha Helix
# Get the sequence from the user
gSeq = prompt("Enter AA sequence (1 char coded)", "")%9999%0
if (gSeq.count > 0) {
if (gSeq[2] == ':') {
gCHAIN = gSeq[1]
gSeq[1] = ' '
gSeq[2] = ' '
gSeq = gSeq%0
}
print format ("Sequence=%s phi=%d psi=%d", gSeq, gPHI, gPSI)
print format ("chain=%s peptide angle=%d pro bump=%d", gCHAIN, gPEPTIDE_ANGLE, gPRO_BUMP)
genAlpha(gSeq)
}
In a webpage
The main script is a small adaptation of the one above. Sequence input has been moved to the webpage. In addition, the helix parameters (which are fixed in the original script) may be changed in the page by a user. The model is generated and displayed in a Jmol object in the page (JmolApplet or JSmol HTML5 object).
The JSmol variant is not working yet. We need debugging the script, something in it fails to run properly in JSmol and no good helix is formed.
See it in action
