Citing a PDB entry:

If you have used the data relating to a specific PDB entry or collection of related entries then please cite the publication describing the entry or entries.

Citing images on the PDBe website:

If using any images provided on the PDBe website, please cite the publication describing the entry that these images represent (as above) and note that the images were taken from the PDBe website.

Cite PDBe:

PDBe: improved findability of macromolecular structure data in the PDB.
Armstrong DR, Berrisford JM, Conroy MJ, Gutmanas A, Anyango S, Choudhary P, Clark AR, Dana JM, Deshpande M, Dunlop R, Gane P, Gáborová R, Gupta D, Haslam P, Koča J, Mak L, Mir S, Mukhopadhyay A, Nadzirin N, Nair S, Paysan-Lafosse T, Pravda L, Sehnal D, Salih O, Smart O, Tolchard J, Varadi M, Svobodova-Vařeková R, Zaki H, Kleywegt GJ, Velankar S.
Nucleic acids research Volume 48 (2020) p.D335-D343
DOI: 10.1093/nar/gkz990

Cite PDBe-KB:

PDBe-KB: a community-driven resource for structural and functional annotations.
PDBe-KB consortium.
Nucleic acids research Volume 48 (2020) p.D344-D353
DOI: 10.1093/nar/gkz853

Cite the PDB archive:

Protein Data Bank: the single global archive for 3D macromolecular structure data.
wwPDB consortium.
Nucleic acids research Volume 47 (2019) p.D520-D528
DOI: 10.1093/nar/gky949

Cite wwPDB:

Announcing the worldwide Protein Data Bank
Helen Berman, Kim Henrick & Haruki Nakamura 
Nature Structural & Molecular Biology 10, 980 (2003)
DOI: 10.1038/nsb1203-980