View source for 1htx


==SOLUTION STRUCTURE OF THE MAIN ALPHA-AMYLASE INHIBITOR FROM AMARANTH SEEDS==
<StructureSection load='1htx' size='340' side='right'caption='[[1htx]]' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1htx]] is a 1 chain structure with sequence from [https://en.wikipedia.org/wiki/Amaranthus_hypochondriacus Amaranthus hypochondriacus]. Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1HTX OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=1HTX FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Solution NMR</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=1htx FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1htx OCA], [https://pdbe.org/1htx PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=1htx RCSB], [https://www.ebi.ac.uk/pdbsum/1htx PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=1htx ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/IAAI_AMAHP IAAI_AMAHP] Alpha-amylase inhibitor. It is active against alpha-amylases from Tribolium castaneum and Prostephanus truncatus larvae.
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== Publication Abstract from PubMed ==
The most abundant alpha-amylase inhibitor (AAI) present in the seeds of Amaranthus hypochondriacus, a variety of the Mexican crop plant amaranth, is the smallest polypeptide (32 residues) known to inhibit alpha-amylase activity of insect larvae while leaving that of mammals unaffected. In solution, 1H NMR reveals that AAI isolated from amaranth seeds adopts a major trans (70%) and minor cis (30%) conformation, resulting from slow cis-trans isomerization of the Val15-Pro16 peptide bond. Both solution structures have been determined using 2D 1H-NMR spectroscopy and XPLOR followed by restrained energy refinement in the consistent-valence force field. For the major isomer, a total of 563 distance restraints, including 55 medium-range and 173 long-range ones, were available from the NOESY spectra. This rather large number of constraints from a protein of such a small size results from a compact fold, imposed through three disulfide bridges arranged in a cysteine-knot motif. The structure of the minor cis isomer has also been determined using a smaller constraint set. It reveals a different backbone conformation in the Pro10-Pro20 segment, while preserving the overall global fold. The energy-refined ensemble of the major isomer, consisting of 20 low-energy conformers with an average backbone rmsd of 0.29 +/- 0.19 A and no violations larger than 0.4 A, represents a considerable improvement in precision over a previously reported and independently performed calculation on AAI obtained through solid-phase synthesis, which was determined with only half the number of medium-range and long-range restraints reported here, and featured the trans isomer only. The resulting differences in ensemble precision have been quantified locally and globally, indicating that, for regions of the backbone and a good fraction of the side chains, the conformation is better defined in the new solution structure. Structural comparison of the solution structure with the X-ray structure of the inhibitor when bound to its alpha-amylase target in Tenebrio molitor shows that the backbone conformation is only slightly adjusted on complexation, while that of the side chains involved in protein-protein contacts is similar to those present in solution. Therefore, the overall conformation of AAI appears to be predisposed to binding to its target alpha-amylase, confirming the view that it acts as a lid on top of the alpha-amylase active site.

Solution structure of the main alpha-amylase inhibitor from amaranth seeds.,Martins JC, Enassar M, Willem R, Wieruzeski JM, Lippens G, Wodak SJ Eur J Biochem. 2001 Apr;268(8):2379-89. PMID:11298757<ref>PMID:11298757</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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== References ==
<references/>
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</StructureSection>
[[Category: Amaranthus hypochondriacus]]
[[Category: Large Structures]]
[[Category: Enassar M]]
[[Category: Lippens G]]
[[Category: Martins JC]]
[[Category: Wieruzeski JM]]
[[Category: Willem R]]
[[Category: Wodak SJ]]