PROTEIN STRUCTURE AND FOLDING
The Solution Structure of Molt-inhibiting Hormone from the Kuruma Prawn Marsupenaeus japonicus *

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Molting in crustaceans is controlled by molt-inhibiting hormone (MIH) and ecdysteroids. It is presumed that MIH inhibits the synthesis and the secretion of ecdysteroids by the Y-organ, resulting in molt suppression. The amino acid sequence of MIH is similar to that of crustacean hyperglycemic hormone (CHH), and therefore, they form a peptide family referred to as the CHH family. Most of the CHH family peptides show no cross-activity, whereas a few peptides show multiple hormonal activities. To reveal the structural basis of this functional specificity, we determined the solution structure of MIH from the Kuruma prawn Marsupenaeus japonicus and compared the solution structure of MIH with a homology-modeled structure of M. japonicus CHH. The solution structure of MIH consisted of five α-helices and no β-structures, constituting a novel structural motif. The homology-modeled structure of M. japonicus CHH was very similar to the solution structure of MIH with the exception of the absence of the N-terminal α-helix and the C-terminal tail, which were sterically close to each other. The surface properties of MIH around this region were quite different from those of CHH. These results strongly suggest that this region is a functionally important site for conferring molt-inhibiting activity.

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Published, JBC Papers in Press, January 7, 2003, DOI 10.1074/jbc.M212962200

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This work was supported in part by Grants-in-aid 11460054 and 1208200 for Scientific Research and the National Project on Protein Structural and Functional Analyses from the Ministry of Education, Culture, Sports, Science and Technology of Japan and by the Uehara Memorial Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The atomic coordinates and the structure factors (code 1J0T) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

Chemical shifts for this peptide were deposited in the BioMagResBank under the entry number 5653.