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Number of Chains (Asymmetric Unit)

Search for structures based on the number of chains in the asymmetric unit.

The asymmetric unit is the smallest portion of a crystal structure to which symmetry operations can be applied in order to generate the complete unit cell (the smallest repeating unit of a crystal). This concept applies to structures determined by X-ray crystallography and is not relevant to structures determined by NMR.

Chains are the individual polymers (macromolecules) contained in a PDB structure. A structure may contain multiple identical chains. Hence, this search option queries for the total number of polymers in the asymmetric unit, regardless of whether that includes multiple identical molecules.


  1. 4HHB contains 4 polymer chains, 2 copies of the hemoglobin alpha chain (chains A and C), and two copies of the hemoglobin beta chain (chains B and D).

    Enter "Between 4 and 4" and press "Submit Query" to return all structures that contain exactly 4 chains in the asymmetric unit. The results include 4HHB.

  2. Enter 30 into the left box, and leave the right box empty. This will query for all structures in the PDB that contain at least 30 chains in the asymmetric unit.