function S = pickSequence(pdbFileName)

% PICKSEQUENCE   Extract sequence from PDB file.
%   seq = pickSequence(pdbFilename, ATOM) reads data from a pdb text
%   file, and extracts the amino acid sequence.
%
%   For documentation of the PDB file format, see
%   http://www.rcsb.org/pdb/docs/format/pdbguide2.2/guide2.2_frame.html

% Define amino acid 3-letter and 1-letter codes
codes_3let = strvcat('ALA', 'ARG', 'ASN', 'ASP', 'CYS', 'GLN', 'GLU', ...
		     'GLY', 'HIS', 'ILE', 'LEU', 'LYS', 'MET', 'PHE', ...
		     'PRO', 'SER', 'THR', 'TRP', 'TYR', 'VAL');
codes_1let = 'ARNDCQEGHILKMFPSTWYVU';

% Read lines until SEQRES is encountered
fid = fopen(pdbFileName);
L = fgetl(fid);
while (~strcmp(L(1:6), 'SEQRES'))
  L = fgetl(fid);
end

% Extract the amino acids
seqnum = 0;
while (strcmp(L(1:6), 'SEQRES'))   % Keep reading SEQRES records
  residues = sscanf(L(20:70), '%3s', [3, inf])';
  for i = 1:length(residues)
    res_index = strmatch(residues(i,:), codes_3let, 'exact');
    if (~isempty(res_index))
      seqnum = seqnum+1;
      seq(seqnum) = codes_1let(res_index);
    end
  end

  L = fgetl(fid);	  % Read the next line
end
fclose(fid);

S = seq(1:seqnum);