1qfd: Difference between revisions

[[Image:1qfd.jpg|left|200px]]<br /><applet load="1qfd" size="350" color="white" frame="true" align="right" spinBox="true"  

alpha-Amylase inhibitor (AAI), a 32-residue miniprotein from the Mexican crop plant amaranth (Amaranthus hypochondriacus), is the smallest known alpha-amylase inhibitor and is specific for insect alpha-amylases (Chagolla-Lopez, A., Blanco-Labra, A., Patthy, A., Sanchez, R., and Pongor, S. (1994) J. Biol. Chem. 269, 23675-23680). Its disulfide topology was confirmed by Edman degradation, and its three-dimensional solution structure was determined by two-dimensional 1H NMR spectroscopy at 500 MHz. Structural constraints (consisting of 348 nuclear Overhauser effect interproton distances, 8 backbone dihedral constraints, and 9 disulfide distance constraints) were used as an input to the X-PLOR program for simulated annealing and energy minimization calculations. The final set of 10 structures had a mean pairwise root mean square deviation of 0.32 A for the backbone atoms and 1.04 A for all heavy atoms. The structure of AAI consists of a short triple-stranded beta-sheet stabilized by three disulfide bonds, forming a typical knottin or inhibitor cystine knot fold found in miniproteins, which binds various macromolecular ligands. When the first intercystine segment of AAI (sequence IPKWNR) was inserted into a homologous position of the spider toxin Huwentoxin I, the resulting chimera showed a significant inhibitory activity, suggesting that this segment takes part in enzyme binding.

1QFD is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Amaranthus_hypochondriacus Amaranthus hypochondriacus]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1QFD OCA].  

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