title: Coordination structures of Mg2+ and Ca2+ in three types of tobacco calmodulins in solution: Fourier-transform infrared spectroscopic studies of side-chain COO- groups.
abstract: Calmodulin (CaM) is a Ca(2+)-binding protein that regulates a number of fundamental cellular activities. Nicotiana tabacum CaM (NtCaM) comprises 13 genes classified into three types, among which gene expression and target enzyme activation differ. We performed Fourier-transform infrared spectroscopy to compare the secondary and coordination structures of Mg(2+) and Ca(2+) among NtCaM1, NtCaM3, and NtCaM13 as representatives of the three types of NtCaMs. Data suggested that NtCaM13 has a different secondary structure due to the weak β-strand bands and the weak 1661 cm(-1) band. Coordination structures of Mg(2+) of NtCaM3 and NtCaM13 were similar but different from that of NtCaM1, while the Ca(2+)-binding manner was similar among the three CaMs. The amplitude differences of the band at 1554-1550 cm(-1) obtained by second-derivative spectra indicated that the intensity change of the band of NtCaM13 was smaller in response to [Ca(2+)] increases under low [Ca(2+)] conditions than were those of NtCaM1 and NtCaM3, while the intensity reached the same level under high [Ca(2+)]. Therefore, NtCaM13 has a characteristic secondary structure and specific Mg(2+)-binding manner and needs higher [Ca(2+)] for bidentate Ca(2+) coordination of 12th Glu in EF-hand motifs. The Ca(2+)-binding mechanisms of the EF-hand motifs of the three CaMs are similar; however, the cation-dependent conformational change in NtCaM13 is unique among the three NtCaMs.
authors.affiliation: Department of Chemistry, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi, Chiba, 263-8522, Japan.
authors.forename: Nanao
authors.initials: N
authors.lastname: Suzuki
authors.forename: Lica Fabiana
authors.initials: LF
authors.lastname: Imai
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kato
authors.forename: Koji
authors.initials: K
authors.lastname: Nagata
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ohashi
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kuchitsu
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.forename: Akira
authors.initials: A
authors.lastname: Sakamoto
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nara
authors.forename: Minoru
authors.initials: M
authors.lastname: Nakano
authors.forename: Naoto
authors.initials: N
authors.lastname: Yonezawa
mesh_terms: D002118:Calcium / Q000737:chemistry; D002147:Calmodulin; D011487:Protein Conformation; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D014026:Nicotiana
chemical_list: D002147:Calmodulin; D012996:Solutions; D002118:Calcium