Jc. Martins et al., H-1-NMR STUDY OF THE SOLUTION STRUCTURE OF AC-AMP2, A SUGAR BINDING ANTIMICROBIAL PROTEIN ISOLATED FROM AMARANTHUS-CAUDATUS, Journal of Molecular Biology, 258(2), 1996, pp. 322-333
The conformation in water of antimicrobial protein 2 from Amaranthus c
audatus (Ac-AMP2) was determined using H-1 NMR, DIANA and restrained m
olecular modeling. Ac-AMP2 is a 30 amino acid residue, lectin-like pro
tein that specifically binds to chitin, a polymer of beta-1,4-N-acetyl
-D-glucosamine. After sequence specific resonance assignments, a total
of 198 distance restraints were collected from 2D NOESY buildup spect
ra at 500 MHz at pH 2, supplemented by a 2D NOESY spectrum at 600 MHz.
The location of the three previously unassigned disulfide bridges was
determined from preliminary DIANA structures, using a statistical ana
lysis of intercystinyl distances. The solution structure of Ac-AMP2 is
presented as a set of 26 DIANA structures, further refined by restrai
ned molecular dynamics using a simulated annealing protocol in the AMB
ER force field, with a backbone r.m.s.d. for the well defined Glu3-Cys
28 segment of 0.69(+/-0.12) Angstrom. The main structural element is a
n antiparallel beta-sheet from Met13 to Lys23 including a beta(I)-turn
over Gln17-Phe18 with a beta bulge at Gly19. Ln addition, a beta'(I)
turn over Arg6-Gly7, a beta'(III) turn over Ser11-Gly12 and a helical
turn from Gly24 to Cys28 are identified. This structure is very simila
r to the equivalent regions of the X-ray structure of wheat germ agglu
tinin and the NMR structure of hevein. (C) 1996 Academic Press Limited