PDBsum entry 1htx

Go to PDB code: 
protein links
Plant protein PDB id
Protein chain
32 a.a.
PDB id:
Name: Plant protein
Title: Solution structure of the main alpha-amylase inhibitor from amaranth seeds
Structure: Alpha-amylase inhibitor aai. Chain: a
Source: Amaranthus hypochondriacus. Grain amaranth. Organism_taxid: 28502. Organ: seeds
NMR struc: 20 models
Authors: J.C.Martins,M.Enassar,R.Willem,J.M.Wieruzeski,G.Lippens, S.J.Wodak
Key ref:
J.C.Martins et al. (2001). Solution structure of the main alpha-amylase inhibitor from amaranth seeds. Eur J Biochem, 268, 2379-2389. PubMed id: 11298757 DOI: 10.1046/j.1432-1327.2001.02118.x
02-Jan-01     Release date:   18-Jul-01    
Go to PROCHECK summary

Protein chain
Pfam   ArchSchema ?
P80403  (IAAI_AMAHP) -  Alpha-amylase inhibitor AAI
32 a.a.
32 a.a.
Key:    PfamB domain  Secondary structure

 Gene Ontology (GO) functional annotation 
  GO annot!
  Biological process     negative regulation of catalytic activity   2 terms 
  Biochemical function     alpha-amylase inhibitor activity     2 terms  


DOI no: 10.1046/j.1432-1327.2001.02118.x Eur J Biochem 268:2379-2389 (2001)
PubMed id: 11298757  
Solution structure of the main alpha-amylase inhibitor from amaranth seeds.
J.C.Martins, M.Enassar, R.Willem, J.M.Wieruzeski, G.Lippens, S.J.Wodak.
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.
  Selected figure(s)  
Figure 2.
Fig. 2. Distribution of the number of NOE distance constraints per residue used as input for the structure calculations. The constraints are specified as follows: filled, intraresidual; cross-hatched, sequential; grey, medium-range (|i–j| < 5); open, long-range.
Figure 4.
Fig. 4. Comparison of the , angle space covered by the nAAI (left) and sAAI (right) ensembles, as demonstrated by Ramachandran plots, computed using the software PROCHECKNMR [34]. Squares indicate non-glycine residues, and glycines are indicated by triangles.
  The above figures are reprinted by permission from the Federation of European Biochemical Societies: Eur J Biochem (2001, 268, 2379-2389) copyright 2001.  
  Figures were selected by an automated process.  

Literature references that cite this PDB file's key reference

  PubMed id Reference
19701660 D.A.Barrio, and M.C.Añón (2010).
Potential antitumor properties of a protein isolate obtained from the seeds of Amaranthus mantegazzianus.
  Eur J Nutr, 49, 73-82.  
11856298 O.L.Franco, D.J.Rigden, F.R.Melo, and M.F.Grossi-De-Sá (2002).
Plant alpha-amylase inhibitors and their interaction with insect alpha-amylases.
  Eur J Biochem, 269, 397-412.  
The most recent references are shown first. Citation data come partly from CiteXplore and partly from an automated harvesting procedure. Note that this is likely to be only a partial list as not all journals are covered by either method. However, we are continually building up the citation data so more and more references will be included with time.