Crystal structure of a 16 kDa double-headed Bowman-Birk trypsin inhibitor from barley seeds at 1.9 Å resolution

Hyun Kyu Song, Young Sil Kim, Jin Kuk Yang, Jinho Moon, Jae Young Lee, Se Won Suh

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56 Citations (Scopus)


The Bowman-Birk trypsin inhibitor from barley seeds (BBBI) consists of 125 amino acid residues with two inhibitory loops. Its crystal structure in the free state has been determined by the multiwavelength anomalous diffraction (MAD) method and has been refined to a crystallographic R-value of 19.1% for 8.0-1.9 Å data. This is the first report on the structure of a 16 kDa double-headed Bowman-Birk inhibitor (BBI) from monocotyledonous plants and provides the highest resolution picture of a BBI to date. The BBBI structure consists of 11 β-strands and the loops connecting these β-strands but it lacks α-helices. BBBI folds into two compact domains of similar tertiary structure. Each domain shares the same overall fold with 8 kDa dicotyledonous BBIs. The five disulfide bridges in each domain are a subset of the seven disulfide bridges in 8 kDa dicotyledonous BBIs. Two buried water molecules form hydrogen bonds to backbone atoms in the core of each domain. One interesting feature of this two-domain inhibitor structure is that the two P1 residues (Arg17 and Arg76) are approximately 40 Å apart, allowing the two reactive-site loops to bind to and to inhibit two trypsin molecules simultaneously and independently. The conformations of the reactive-site loops of BBBI are highly similar to those of other substrate-like inhibitors. This structure provides the framework for modeling of the 1:2 complex between BBBI and trypsin.

Original languageEnglish
Pages (from-to)1133-1144
Number of pages12
JournalJournal of Molecular Biology
Issue number5
Publication statusPublished - 1999 Nov 12
Externally publishedYes

Bibliographical note

Funding Information:
We thank Drs L. Flak and J. Berendzen of beamline X8-C at National Synchrotron Light Source, Brookhaven National Laboratory, USA and Professor N. Sakabe and Dr N. Watanabe of the beamline BL-6A2, Photon Factory, KEK, Japan for their assistance with synchrotron X-ray data collection. We thank Drs P. Flecker and L.-O. Essen for kindly providing us the coordinates of the soybean Bowman-Birk inhibitor. This work was supported by the Center for Molecular Catalysis, Seoul National University, Korea Science and Engineering Foundation, and Korea Ministry of Education, Basic Sciences Research Institute. The Inter-University Center for Natural Science Research Facilities, Seoul National University is also thanked for providing the X-ray equipment, which is partially supported by the Specialization Fund from KOSEF. H.K.S. is supported by a Postdoctoral Fellowship from the Korea Ministry of Education.


  • Bowman-Birk trypsin inhibitor
  • Double-headed inhibitor
  • Gene duplication
  • Monocotyledonous plant
  • Reactive-site loop

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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