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Revision as of 06:12, 28 May 2008

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Template:STRUCTURE 2k3s

HADDOCK-derived structure of the CH-domain of the smoothelin-like 1 complexed with the C-domain of apocalmodulin

Overview

The smoothelin-like 1 protein (SMTNL1) is a recently discovered component of smooth muscle tissues [Borman M. A., MacDonald J. A., and Haystead T. A. J., (2004) FEBS Lett. 573, 207-213]. This 459-residue protein contains a single type-2 CH-domain at its C-terminus that shares sequence identity with the smoothelin family of smooth muscle specific proteins. In contrast to the smoothelins, SMTNL1 does not associate with F-actin in vitro, and although it is known to become phosphorylated during cGMP-mediated Ca(2+)-desensitization and relaxation, its specific role in smooth muscle remains unclear. In addition, the biological function of the C-terminal CH-domains found in the smoothelin proteins is also poorly understood. In this work, we have therefore determined the solution structure of the CH-domain of mouse SMTNL1 (SMTNL1-CH; residues 346-459). The secondary structure and the overall fold for the C-terminal type-2 CH-domain is very similar to that of other CH-domains. However, two clusters of basic residues form a unique surface structure that is characteristic of SMTNL1-CH. Moreover, the protein has an extended C-terminal a-helix, which contains a calmodulin (CaM)-binding IQ-motif, that is also a distinct feature of the smoothelins. We have characterized the binding of apo-CaM to SMTNL1-CH through its IQ-motif by isothermal titration calorimetry and NMR chemical shift perturbation studies. In addition, we have used the HADDOCK protein-protein docking approach to construct a model for the complex of apo-CaM and SMTNL1-CH. The model revealed a close interaction of SMTNL1-CH with the two Ca(2+)-binding loop regions of the C-domain of apo-CaM; this mode of apo-CaM binding is distinct from previously reported interactions of apo-CaM with IQ-motifs. Finally, we comment on the putative role of the CH-domain in the biological function of the SMTNL1 protein.

About this Structure

2K3S is a Protein complex structure of sequences from Mus musculus and Xenopus laevis. Full crystallographic information is available from OCA.

Reference

Solution structure of the calponin homology (CH)-domain from the smoothelin-like 1 protein: a unique Apo-calmodulin binding mode and the possible role of the C-terminal type 2 CH-domain in smooth muscle relaxation., Ishida H, Borman Meredith A, Ostrander J, Vogel Hans J, Macdonald Justin A, J Biol Chem. 2008 May 12;. PMID:18477568 Page seeded by OCA on Wed May 28 09:12:42 2008