title: Three-dimensional structure topology of the calreticulin P-domain based on NMR assignment.
abstract: Calreticulin (CRT) is an abundant molecular chaperone of the endoplasmic reticulum. Its central, proline-rich P-domain, comprising residues 189-288, contains three copies of each of two repeat sequences (types 1 and 2), which are arranged in a characteristic '111222' pattern. Here we show that the three-dimensional structure of CRT(189-288) contains a single hairpin fold formed by the entire polypeptide chain. The loop at the bottom of the hairpin consists of residues 227-247, and is closed by an anti-parallel beta-sheet of residues 224-226 and 248-250. Two additional beta-sheets contain residues 207-209 and 262-264, and 190-192 and 276-278. The 17-residue spacing of the beta-strands in the N-terminal part of the hairpin and the 14-residue spacing in the C-terminal part reflect the length of the type 1 and type 2 sequence repeats. As a consequence of this topology the peptide segments separating the beta-strands in the N-terminal part of the hairpin are likely to form bulges to accommodate the extra residues. These results are based on nearly complete sequence-specific NMR assignments for CRT(189-288), which were obtained using standard NMR techniques with the (13)C/(15)N-labeled protein, and collection of nuclear Overhauser enhancement upper distance constraints.
authors.affiliation: Institut für Biochemie, Eidgenössische Technische Hochschule, Zurich, Switzerland.
authors.forename: L
authors.initials: L
authors.lastname: Ellgaard
authors.forename: R
authors.initials: R
authors.lastname: Riek
authors.forename: D
authors.initials: D
authors.lastname: Braun
authors.forename: T
authors.initials: T
authors.lastname: Herrmann
authors.forename: A
authors.initials: A
authors.lastname: Helenius
authors.forename: K
authors.initials: K
authors.lastname: Wüthrich
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D037282:Calreticulin; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry*; D011392:Proline / Q000032:analysis; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D020449:Repetitive Sequences, Amino Acid; D012261:Ribonucleoproteins / Q000737:chemistry*; D012996:Solutions
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D010446:Peptide Fragments; D012261:Ribonucleoproteins; D012996:Solutions; D011392:Proline