title: Crystal structures of sodium-bound annexin A4.
abstract: Annexin A4 (Anx4) possesses four repeat domains with one Ca(2+)-binding site (CBS) in each domain. In this study, we resolved two crystal structures of the Na(+)-bound form at high resolution (1.58 and 1.35 A). This is the first report that Anx4 binds the Na(+) ion in CBSs. Electron density maps, valence screening, and atomic absorbance spectrometry confirmed that Anx4 bound the Na(+) ion. One structure (1.58 A) bound the Na(+) ion in CBS I, whereas another structure (1.35 A) bound the Na(+) ion in CBS II and CBS III. We compared the two Na(+)-bound forms by superimposing their C(alpha) traces. The C(alpha) atoms of CBS III largely moved by coordination of the Na(+) ion. In the C(alpha) atoms of CBS I, however, little change resulted from Na(+)-coordination. Only the side chain of Glu71 was moved by Na(+)-coordination in CBS I. These results indicate that Anx4 also binds not only Ca(2+) but also Na(+) ion in the CBS.
authors.affiliation: Biological Science Course, Graduate School of Science and Engineering, Aoyama Gakuin University, Sagamihara, Kanagawa, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Butsushita
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Fukuoka
authors.forename: Koh
authors.initials: K
authors.lastname: Ida
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Arii
mesh_terms: D000042:Absorption; D000595:Amino Acid Sequence; D000818:Animals; D017314:Annexin A4 / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009068:Movement; D017433:Protein Structure, Secondary; D051381:Rats; D012964:Sodium / Q000378:metabolism*
chemical_list: D017314:Annexin A4; D012964:Sodium; D002118:Calcium