Acta Cryst. (2013). D69, 2017-2026 [ doi:10.1107/S0907444913018015 ]
Abstract: The first crystal structure of a barwin-like protein, named carwin, has been determined at high resolution by single-wavelength anomalous diffraction (SAD) phasing using the six intrinsic S atoms present in the protein. The barwin-like protein was purified from Carica papaya latex and crystallized in the orthorhombic space group P212121. Using in-house Cu K X-ray radiation, 16 cumulative diffraction data sets were acquired to increase the signal-to-noise level and thereby the anomalous scattering signal. A sequence-database search on the papaya genome identified two carwin isoforms of 122 residues in length, both containing six S atoms that yield an estimated Bijvoet ratio of 0.93% at 1.54 Å wavelength. A systematic analysis of data quality and redundancy was performed to assess the capacity to locate the S atoms and to phase the data. It was observed that the crystal decay was low during data collection and that successful S-SAD phasing could be obtained with a relatively low data multiplicity of about 7. Using a synchrotron source, high-resolution data (1 Å) were collected from two different crystal forms of the papaya latex carwin. The refined structures showed a central -barrel of six strands surrounded by several -helices and loops. The -barrel of carwin appears to be a common structural module that is shared within several other unrelated proteins. Finally, the possible biological function of the protein is discussed.
PDB references: 4jp6 and 4jp7
Keywords: sulfur-SAD phasing; barwin-like protein; carwin; Carica papaya.
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