Why there are multiple versions of a protein sequence in PDB FASTA downloaded file?

Question

[jafarzadeh91]

Sorry if the question is banal, I search but didn't find an explanation.Recently I downloaded 4HHB Protein sequence from PDB but actually the file contains four sequences with names 4HHB:A, 4HHB:B, 4HHB:C, 4HHB:D. It is like the below:

>4HHB:A|PDBID|CHAIN|SEQUENCE
A sequence....
>4HHB:B|PDBID|CHAIN|SEQUENCE
A sequence...
>4HHB:C|PDBID|CHAIN|SEQUENCE
A sequence...
>4HHB:D|PDBID|CHAIN|SEQUENCE
A sequence...

I would be appreciate if provide me with a resource or explain me what are those four sequences exactly and what is the difference between them?

Answer 1

[GenoMax]

Data in PDB is represented in asymmetric units which are put together to make the biological assemblies. There is a nice tutorial here: http://pdb101.rcsb.org/learn/guide-to-understanding-pdb-data/biological-assemblies

In the protein you are referring to there are a total of 4 chains (so the 4 sequences) but they represent 2 sequence unique identities (A/C are identical, as are B/D). http://www.rcsb.org/pdb/explore/remediatedSequence.do?params.chainEntityStrategyStr=first&structureId=4HHB

[jafarzadeh91]

Thanks a lot.

Answer 2

[roy.granit]

Each of these represent a different peptide chain that together compose the entire protein. e.g 4HHB:A = chain #1. This protein has a total of four different chains

[jafarzadeh91]

Thank you a lot roy.