Structural studies of Impatiens balsamina antimicrobial protein (Ib-AMP1)

被引:48
作者
Patel, SU
Osborn, R
Rees, S
Thornton, JM
机构
[1] Univ London Univ Coll, Dept Biochem & Mol Biol, Biomol Struct & Modelling Unit, London WC1E 6BT, England
[2] Zeneca Agrochem, Jealotts Hill Res Stn, Bracknell RG42 6ET, Berks, England
关键词
D O I
10.1021/bi971747d
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Structural studies of Ib-AMP1, a small antimicrobial peptide derived from the seeds of Impatiens balsamina have been performed using circular dichroism (CD) and two-dimensional proton nuclear magnetic resonance (H-1 NMR), This 20-residue peptide is highly basic with five arginine residues and contains four cysteines which form two intramolecular disulfide bonds, CD results reveal that the peptide may include a beta-turn but do not show evidence for either helical or beta-sheet structure over a range of temperature and pH. Structural information from NMR was obtained in the form of proton-proton internuclear distances inferred from NOEs and dihedral angle restraints from spin-spin coupling constants, which were used for distance geometry calculations. Owing to the difficulty in obtaining the correct disulfide connectivities by chemical methods, three separate calculations were performed; with no disulfides and with the two possible alternate disulfide connectivities. Results from distance geometry calculations reveal that although the peptide is small, the cysteines constrain part of it to adopt a well-defined main chain conformation. From residue 6 to 20, the backbone is well defined, whilst the N-terminal region, residues 1-5, has very few constraints and appears to be very flexible, In the defined core region, there are three beta-turns at residues 9-12, 10-13, and 12-15. The side chains show no strong interactions in the NMR spectra and are therefore thought to adopt multiple conformations. Superposition of the structures generated shows that the peptide has two hydrophilic patches which are at opposite ends of the molecule separated by a large hydrophobic patch. Little is known about the mode of action of this protein, but it is thought to interact with a membrane-bound receptor, and possible sites of interaction are discussed, The structures determined are compared with those of the a-conotoxins, which are also highly basic proteins with similar disulfide connectivities.
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页码:983 / 990
页数:8
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