Open AccessStructure of calcium‐bound human S100A13 at pH 7.5 at 1.8 Å resolution
Author(s) -
Imai Fabiana Lica,
Nagata Koji,
Yonezawa Naoto,
Nakano Minoru,
Tanokura Masaru
Publication year - 2008
Publication title -
acta crystallographica section f
Language(s) - English
Resource type - Journals
ISSN - 1744-3091
DOI - 10.1107/s1744309107068236
Subject(s) - dimer , chemistry , endoplasmic reticulum , helix (gastropod) , hydrogen bond , protein structure , crystallography , calcium , stereochemistry , biochemistry , molecule , biology , ecology , organic chemistry , snail
S100A13 is a member of the S100 family of EF‐hand‐containing calcium‐binding proteins. S100A13 plays an important role in the secretion of fibroblast growth factor‐1 and interleukin 1α, two pro‐angiogenic factors released by the nonclassical endoplasmic reticulum/Golgi‐independent secretory pathway. The X‐ray crystal structure of human S100A13 at pH 7.5 was determined at 1.8 Å resolution. The structure was solved by molecular replacement and was refined to a final R factor of 19.0%. The structure revealed that human S100A13 exists as a homodimer with two calcium ions bound to each protomer. The protomer is composed of four α‐helices (α 1 –α 4 ), which form a pair of EF‐hand motifs. Dimerization occurs by hydrophobic interactions between helices α 1 and α 4 and by intermolecular hydrogen bonds between residues from helix α 1 and the residues between α 2 and α 3 of both chains. Despite the high similarity of the backbone conformation in each protomer, the crystal structures of human S100A13 at pH 7.5 (this study) and at pH 6.0 [Li et al. (2007), Biochem. Biophys. Res. Commun . 356 , 616–621] exhibit recognizable differences in the relative orientation (∼2.5°) of the protomers within the dimer and also remarkable differences in the side‐chain conformations of several amino‐acid residues.