File.open('ppi.v10.homo.sapiens.700.txt', 'w') do |fout|
  File.open('protein.links.detailed.v10.homo.sapiens.txt').each do |line|
    col = line.chomp.split("\t")
    next unless (col[0] = protein2symbol[col[0]]) && (col[1] = protein2symbol[col[1]])
    next unless col.last.to_i >= 700