1htx
From Proteopedia
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SOLUTION STRUCTURE OF THE MAIN ALPHA-AMYLASE INHIBITOR FROM AMARANTH SEEDS
Overview
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.
About this Structure
1HTX is a Single protein structure of sequence from Amaranthus hypochondriacus. Full crystallographic information is available from OCA.
Reference
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
Page seeded by OCA on Tue Nov 20 16:49:36 2007
