title: Missing strings of residues in protein crystal structures.
abstract: A large fraction of the protein crystal structures deposited in the Protein Data Bank are incomplete, since the position of one or more residues is not reported, despite these residues are part of the material that was analyzed. This may bias the use of the protein crystal structures by molecular biologists. Here we observe that in the large majority of the protein crystal structures strings of residues are missing. Polar residues incline to occur in missing strings together with glycine, while apolar and aromatic residues tend to avoid them. Particularly flexible residues, as shown by their extremely high B-factors, by their exposure to the solvent and by their secondary structures, flank the missing strings. These data should be a helpful guideline for crystallographers that encounter regions of flat and uninterpretable electron density as well as end-users of crystal structures.
authors.affiliation: Department of Structural and Computational Biology; Max F. Perutz Laboratories, Vienna University, Vienna Biocenter (VBC); Vienna, Austria; Department of Biochemistry; Faculty of Chemistry and Chemical Technology, University of Ljubljana; Ljubljana, Slovenia.
authors.forename: Kristina
authors.initials: K
authors.lastname: Djinovic-Carugo
authors.affiliation: Department of Structural and Computational Biology; Max F. Perutz Laboratories, Vienna University, Vienna Biocenter (VBC); Vienna, Austria; Department of Chemistry; Pavia University; Pavia, Italy.
authors.forename: Oliviero
authors.initials: O
authors.lastname: Carugo
keywords: conformational disorder; disordered proteins; missing atoms; missing residues; protein crystal structure; protein data bank; structural bioinformatics; unfolded proteins