Coordination structures of Mg super(2+) and Ca super(2+) in three types of tobacco calmodulins in solution: Fourier-transform infrared spectroscopic studies of side-chain COO super(-) groups

• Published in: Biopolymers 2013-07, Vol.99 (7), p.472-483
• Main Authors: Suzuki, Nanao, Imai, Lica Fabiana, Kato, Yusuke, Nagata, Koji, Ohashi, Yuko, Kuchitsu, Kazuyuki, Tanokura, Masaru, Sakamoto, Akira, Nara, Masayuki, Nakano, Minoru, Yonezawa, Naoto
• Format: Article
• Language: English
• Subjects: Nicotiana tabacum
• ISSN: 0006-3525; 1097-0282
• DOI: 10.1002/bip.22203

Calmodulin (CaM) is a Ca super(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 super(2+) and Ca super(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 beta -strand bands and the weak 1661 cm super(-1) band. Coordination structures of Mg super(2+) of NtCaM3 and NtCaM13 were similar but different from that of NtCaM1, while the Ca super(2+)-binding manner was similar among the three CaMs. The amplitude differences of the band at 1554-1550 cm super(-1) obtained by second-derivative spectra indicated that the intensity change of the band of NtCaM13 was smaller in response to [Ca super(2+)] increases under low [Ca super(2+)] conditions than were those of NtCaM1 and NtCaM3, while the intensity reached the same level under high [Ca super(2+)]. Therefore, NtCaM13 has a characteristic secondary structure and specific Mg super(2+)-binding manner and needs higher [Ca super(2+)] for bidentate Ca super(2+) coordination of 12th Glu in EF-hand motifs. The Ca super(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. [copy 2013 Wiley Periodicals, Inc. Biopolymers 99: 472-483, 2013.