The whole is not the simple sum of its parts in calmodulin from S. cerevisiae.
Calmodulin is an essential Ca(2+)-binding protein involved in a multitude of cellular processes. The calmodulin sequence is highly conserved among all eukaryotic species; calmodulin from the yeast S. cerevisiae (yCaM) is the most divergent form, while still sharing 60% sequence identity with vertebrate calmodulin (vCaM). Although yCaM can be functionally substituted by vCaM in vivo, the two calmodulin proteins possess significantly different Ca(2+)-binding properties as well as abilities to activate vertebrate target enzymes in vitro. In addition, it has been observed that certain properties of the N-terminal and C-terminal domains of Ca(2+)-yCaM differ depending on whether they are in the context of the whole protein or isolated as half-molecule fragments. To investigate the structural basis for these differing properties, we have undertaken nuclear magnetic resonance (NMR) studies on yCaM and the two half-molecule fragments representing its two individual domains, yTr1(residues 1-76) and yTr2 (residues 75-146). We present direct evidence that the two domains of Ca(2+)-yCaM interact via their exposed hydrophobic surfaces. Thus, the Ca(2+)-bound form of yCaM exists in a novel compact structure in direct contrast to the well-established structure of Ca(2+)-vCaM comprised of two independent globular domains.
Lee
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Department of Biochemistry, Biomolecular Structure Center, Box 357742, University of Washington, Seattle, Washington 98195-7742, USA.
Klevit
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D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism*; D020832:EF Hand Motifs; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000737:chemistry*; D013329:Structure-Activity Relationship; D017186:Titrimetry
D002147:Calmodulin; D010446:Peptide Fragments; D002118:Calcium