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PDBsum entry 2ab9
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Hydrolase inhibitor
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PDB id
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2ab9
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References listed in PDB file
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Key reference
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Title
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Discovery, Structural determination, And putative processing of the precursor protein that produces the cyclic trypsin inhibitor sunflower trypsin inhibitor 1.
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Authors
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J.P.Mulvenna,
F.M.Foley,
D.J.Craik.
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Ref.
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J Biol Chem, 2005,
280,
32245-32253.
[DOI no: ]
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PubMed id
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Abstract
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Backbone-cyclized proteins are becoming increasingly well known, although the
mechanism by which they are processed from linear precursors is poorly
understood. In this report the sequence and structure of the linear precursor of
a cyclic trypsin inhibitor, sunflower trypsin inhibitor 1 (SFTI-1) from
sunflower seeds, is described. The structure indicates that the major elements
of the reactive site loop of SFTI-1 are present before processing. This may have
importance for a protease-mediated cyclizing reaction as the rigidity of SFTI-1
may drive the equilibrium of the reaction catalyzed by proteolytic enzymes
toward the formation of a peptide bond rather than the normal cleavage reaction.
The occurrence of residues in the SFTI-1 precursor susceptible to cleavage by
asparaginyl proteases strengthens theories that involve this enzyme in the
processing of SFTI-1 and further implicates it in the processing of another
family of plant cyclic proteins, the cyclotides. The precursor reported here
also indicates that despite strong active site sequence homology, SFTI-1 has no
other similarities with the Bowman-Birk trypsin inhibitors, presenting
interesting evolutionary questions.
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Figure 1.
FIGURE 1. A ribbon depiction of the structure of a BBI from
Glycine max (soybean, PDB code 1BBI [PDB]
) with the chymotrypsin and trypsin-reactive loops highlighted
is shown. The detailed structure of the trypsin inhibitory loop
is shown below the ribbon diagram and alongside the solution
structure of SFTI-1 (PDB code 1JBL [PDB]
). In both cases the Cys residues and the lysine residue in the
P1 position (45) are highlighted with the side chains depicted
in stick form. The inset shows SFTI-1 (PDB code 1JBL [PDB]
) superimposed with the reactive loops of BBIs from mung bean
(PDB code 1SMF [PDB]
), adzuki bean (PDB code 1TAB [PDB]
), and soybean (PDB code 1BBI [PDB]
). For orientation purposes, the Cys residues have been labeled
on SFTI-1.
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Figure 6.
FIGURE 6. Superimposition of the reactive site loops of
pro-SFTI-1 (PDB ID 2AB9 [PDB]
), cyclic SFTI-1 (PDB ID 1JBL [PDB]
), and the trypsin inhibitory loop of the soybean BBI (PDB ID
1BBI [PDB]
). Cys residues are highlighted, and the Cys numbering of
pro-SFTI-1 is indicated for reference.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
32245-32253)
copyright 2005.
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