Chains and heterogens:
PDB Chain Sequences:
>1btu_ (-) vvggteaqrnswpsqislqyrsgsswahtcggtlirqnwvmtaahcvdreltfrvvvgeh nlnqnngteqyvgvqkivvhpywntddvaagydiallrlaqsvtlnsyvqlgvlpragti lannspcyitgwgltrtngqlaqtlqqaylptvdyaicssssywgstvknsmvcaggdgv rsgcqgdsggplhclvngqyavhgvtsfvsrlgcnvtrkptvftrvsayiswinnviasn