How to read the "SEQRES" section from a PDB file, using R I'm using R and its Rpdb package to work with PDB files. I use the read.pdb function but, nevertheless, I couldn't find the argument which will allow me to view the SEQRES section and the full amino-acid sequence of the protein.

For example, I want to find which amino-acid is in the 17th position of the sequence and I want to extract it from the 'SRQRES' section in the PDB file (the original length of the sequence was reduced for the sake of the example):

SEQRES   1 A  390  GLU PRO GLU TRP THR TYR PRO ARG LEU SER CYS GLN GLY          
SEQRES   2 A  390  SER THR PHE GLN LYS ALA LEU LEU ILE SER PRO HIS ARG          
SEQRES   3 A  390  PHE GLY GLU ALA ARG GLY ASN SER ALA PRO LEU ILE ILE          
SEQRES   4 A  390  ARG GLU PRO PHE ILE ALA CYS GLY PRO LYS GLU CYS LYS          
SEQRES   5 A  390  HIS PHE ALA LEU THR HIS TYR ALA ALA GLN PRO GLY GLY          
SEQRES   6 A  390  TYR TYR ASN GLY THR ARG GLU ASP ARG ASN LYS LEU ARG          
SEQRES   7 A  390  HIS LEU ILE SER VAL LYS LEU GLY LYS ILE PRO THR VAL          
SEQRES   8 A  390  GLU ASN SER ILE PHE HIS MET ALA ALA TRP SER GLY SER          
SEQRES   9 A  390  ALA CYS HIS ASP GLY ARG GLU TRP THR TYR ILE GLY VAL          
SEQRES  10 A  390  ASP GLY PRO ASP SER ASN ALA LEU ILE LYS ILE LYS TYR          


...   

The original file can be found here 1a4g.pdb.

Any ideas on how to accomplish that?
I have not used Rpdb but I have used, and would recommend, bio3d.

To read the PDB file 1A4G:

library(bio3d)
pdb1a4g &lt;- read.pdb("1a4g")


To get the SEQRES information, there are two options. Get it from the pdb object directly:

seq1a4g &lt;- pdb1a4g$seqres


Or call pdbseq:

seq1a4g &lt;- pdbseq(pdb1a4g)


Using the second method, the 17th position (note this is not the same as the 17th position of the original protein sequence):

seq1a4g[17]
 92 
"Q"